Question Bank

EC8701- Antennas and Microwave Engineering Department of ECE 2020-2021
EC8701 ANTENNAS AND MICROWAVE ENGINEERING L T P C

3 0 0 3
OBJECTIVES:
• To enable the student to understand the basic principles in antenna and microwave system
design
• To enhance the student knowledge in the area of various antenna designs
• To enhance the student knowledge in the area of microwave components and antenna for
practical applications.
UNIT I INTRODUCTION TO MICROWAVE SYSTEMS AND ANTENNAS 9

Microwave frequency bands, Physical concept of radiation, Near- and far-field regions, Fields
and Power Radiated by an Antenna, Antenna Pattern Characteristics, Antenna Gain and
Efficiency, Aperture Efficiency and Effective Area, Antenna Noise Temperature and G/T,
Impedance matching, Friis transmission equation, Link budget and link margin, Noise
Characterization of a microwave receiver.
UNIT II RADIATION MECHANISMS AND DESIGN ASPECTS 9
Radiation Mechanisms of Linear Wire and Loop antennas, Aperture antennas, Reflector
antennas, Microstrip antennas and Frequency independent antennas, Design considerations and
applications.
UNIT III ANTENNA ARRAYS AND APPLICATIONS 9
Two-element array, Array factor, Pattern multiplication, uniformly spaced arrays with
uniform and non-uniform excitation amplitudes, Smart antennas.
UNIT IV PASSIVE AND ACTIVE MICROWAVE DEVICES 9
Microwave Passive components: Directional Coupler, Power Divider, Magic Tee, attenuator,
resonator, Principles of Microwave Semiconductor Devices: Gunn Diodes, IMPATT
diodes Schottky Barrier diodes, PIN diodes, Microwave tubes: Klystron, TWT, Magnetron.
UNIT V MICROWAVE DESIGN PRINCIPLES 9
Impedance transformation, Impedance Matching, Microwave Filter Design, RF and Microwave
Amplifier Design, Microwave Power amplifier Design, Low Noise Amplifier Design,
Microwave Mixer Design, Microwave Oscillator Design
OUTCOMES:
The student should be able to:
• Apply the basic principles and evaluate antenna parameters and link power budgets
• Design and assess the performance of various antennas
• Design a microwave system given the application specifications.
TEXTBOOKS:
1. John D Krauss, Ronald J Marhefka and Ahmad S. Khan, “Antenna and Wave Propagation:
Fourth Edition, Tata McGraw –Hill, 2006. (UNITI, II, III)
2. David M.Pozar, “Microwave Engineering”, Fourth Edition, Wiley India, 2012. (UNIT I, IV,
V).
REFERENCES:
1. Constantine A.Balanis,”Antenna Theory Analysis and Design”, Third edition, John Wiley
India Pvt Ltd., 2005.
2. R.E.Collin, “Fundamentals for Microwave Engineering”, Second edition, IEEE Press, 2001.
St. Joseph’s College of Engineering / St. Joseph’s Institute of Technology 1

COURSE OUTCOMES
Upon Completion of the course, the students will be able to
Understand the theoretical principles and basic of Microwave evaluate the Antenna
C401.1
parameters.
C401.2 Design and assess the performance of different types of Antennas.
C401.3 Understand and acquire knowledge about Antenna and Array and its application.
C401.4 Ability to analyze the microwave active and passive components such as Power dividers,
hybrid junctions and understand the operational concepts of microwave vacuum tubes based
oscillators and amplifiers.
C401.5 Ability to Design a Microwave amplifier and oscillator system for practical application
specifications.
MAPPING BETWEEN CO AND PO, PSO WITH CORRELATION LEVEL 1/2/3

PO PO PO PO PO PO PO PO PO PO PO PO PS PS PS
EC8701
1 2 3 4 5 6 7 8 9 10 11 12 O1 O2 O3
C401.1 3 2 3 3 1 1 2 1 1 2 1 3 3 3 2
C401.2 3 2 3 3 1 1 2 1 1 2 1 3 3 3 2
C401.3 3 2 3 3 1 1 2 1 1 2 1 3 3 3 2
C401.4 3 2 3 3 1 1 2 1 1 2 1 3 3 3 2
C401.5 3 2 3 3 1 1 2 1 1 2 1 3 3 3 2
UNIT- I INTRODUCTION TO MICROWAVE SYSTEMS AND ANTENNAS

Sl. Knowledge Course
Course Content
No. level Outcomes
1 U, R Introduction and basic principles of Microwave and Antenna
2 U,R Microwave frequency bands, Physical concept of radiation, Near-
and far-field regions
3 U Fields and Power Radiated by an Antenna
4 U,R Antenna Pattern Characteristics, Antenna Gain and Efficiency
C401.1
5 U, An Aperture Efficiency and Effective Area
6 U,R,An Antenna Noise Temperature and G/T
7 U,R,An Impedance matching, Friis transmission equation
8 U, R, An Link budget and link margin
9 U Noise Characterization of a microwave receiver.
UNIT – II RADIATION MECHANISMS AND DESIGN ASPECTS
Course Content
No. Level Outcomes
1 U Introduction to Radiation Mechanism and Design Aspects
2 U,An,R Radiation Mechanisms of Linear Wire
3 U,An,R Radiation Mechanisms of Loop antennas
C401.2
4 U,R Aperture antennas
5 U,R Reflector antennas
6 U,R Microstrip antennas
7 U,R Frequency independent antennas
8 U, An Design considerations
9 U, Ap Applications
UNIT-III ANTENNA ARRAYS AND APPLICATIONS
Course Content
No. Level Outcomes
1 U Introduction to Antenna Arrays
2 U Two-element array
3 U, An Array factor
4 U, An Pattern multiplication
5 U,An Uniformly spaced arrays C401.3
6 U,An Uniformly spaced arrays with uniform excitation amplitudes
7 U,An Uniformly spaced arrays with non-uniform excitation amplitudes
8 R,U,An Smart antennas
9 R,U,An Application
UNIT – IV PASSIVE AND ACTIVE MICROWAVE DEVICES
Course Content
No. Level Outcomes
1 U Microwave Passive components
2 U Directional Coupler
3 U,R Power Divider
4 U,R Magic Tee, attenuator, resonator
5 U Principles of Microwave Semiconductor Devices
C401.4
6 U, R Gunn Diodes
7 U, R IMPATT diodes Schottky Barrier diodes, PIN diodes
8 U, R.An Microwave tubes: Klystron
9 U, R TWT (Travelling wave tube)
10 U, R,An Magnetron
UNIT-V MICROWAVE DESIGN PRINCIPLES
Course Content
No. Level Outcomes
1 U Impedance transformation
2 U Impedance Matching
3 U, An,Ap Microwave Filter Design
4 U,An,Ap RF and Microwave Amplifier Design C401.5
5 U,An,Ap Microwave Power amplifier Design
6 U, An,Ap Low Noise Amplifier Design
7 U, An,Ap Microwave Mixer Design
8 U,An,Ap Microwave Oscillator Design
Ap – Apply; An – Analyze; U – Understand; R- Remember

UNIT - I INTRODUCTION TO MICROWAVE SYSTEMS AND ANTENNAS
PART A - C401.1
1.Sketch electromagnetic frequency spectrum showing the location of RF and Microwave
frequency bands.
2. Define microwave.
Microwaves are electromagnetic waves (EM) with wavelengths ranging from 1mm to
1m. The corresponding frequency range is 300MHz to 300 GHz.
3. List the conditions under which wire radiates.

(i)If charge is moving with a uniform velocity( current created):
a. There is no radiation if the wire is straight, and infinite in extent.
b. There is radiation if the wire is curved, bent, discontinuous, terminated, or
truncated.
(ii) If charge is oscillating in a time-motion, it radiates even if the wire is straight.
4.Define reactive near field region of antenna.

Reactive near-field region is defined as “that portion of the near-field region immediately
surrounding the antenna wherein the reactive field predominates.” For most antennas, the outer
3
boundary of this region is commonly taken to exist at a distance 𝑅 < 0.62√𝐷 ⁄𝜆 from the
antenna surface, where λ is the wavelength and D is the largest dimension of the antenna.
5. Define radiating near field region( Fresnel region) of antenna.

Radiating near-field (Fresnel) region is defined as “that region of the field of an antenna between
the reactive near-field region and the far-field region wherein radiation fields predominate and
wherein the angular field distribution is dependent upon the distance from the antenna.

3
The inner boundary is taken to be the distance 𝑅 ≥ 0.62√𝐷 ⁄𝜆 and the outer boundary is taken
to be the distance R < 2D2/λ where D is the largest dimension of the antenna.
6. Define far field( Fraunhofer) region of antenna

Far-field (Fraunhofer) region is defined as “that region of the field of an antenna where the
angular field distribution is essentially independent of the distance from the antenna. If the
antenna has a maximum overall dimension D, the far-field region is commonly taken to exist at
distances greater than 2D2/λ from the antenna, λ being the wavelength.
7.A parabolic reflector antenna used for reception with the direct broadcast system (DBS)
is 18 inches in diameter and operates at 12.4 GHz. Find the far-field distance for this
antenna.
The operating wavelength at 12.4 GHz is λ = c/ f =( 3 × 108 )/(12.4 × 109) = 2.42 cm.
D= 18 inches= 18x0.0254=0.457m
The far-field distance is Rff = 2D2 / λ = 2(0.457)2/ 0.0242 = 17.3 m.
8. Define Radiation Intensity. What is it’s significance?

Radiation Intensity 𝑈(𝜃, ∅) in given direction is defined as the power per unit solid angle
in that direction.
• The power radiated per unit area in any direction is given by pointing vector P.
• For distant field for which E and H are orthogonal in a plane normal to the radius vector,
E2
The power flow per unit area is given by P = watts / sqm
v
• 2
There are r square meters of surface area per unit solid angle( or steradian).
𝑟 2𝐸2
• 𝑈(𝜃, ∅) = 𝑟 2 𝑃 = 𝑤𝑎𝑡𝑡𝑠/𝑢𝑛𝑖𝑡 𝑠𝑜𝑙𝑖𝑑 𝑎𝑛𝑔𝑙𝑒
𝜂𝑣
The radiation intensity gives the variation in radiated power versus position around the antenna.
We can find the total power radiated by the antenna by integrating the Poynting vector over the
surface of a sphere that encloses the antenna. This is equivalent to integrating the radiation
intensity over a unit sphere.
2𝜋 𝜋
𝑃𝑟𝑎𝑑 = 𝑃𝑜𝑤𝑒𝑟 𝑟𝑎𝑑𝑖𝑎𝑡𝑒𝑑 = ∫ ∫ 𝑈(𝜃, ∅)𝑠𝑖𝑛𝜃𝑑𝜃𝑑∅

∅=0 𝜃=0
9. Define Radiation pattern.

The radiation pattern of an antenna is a plot of the magnitude of the far-zone field strength
versus position around the antenna, at a fixed distance from the antenna.
Thus the radiation pattern can be plotted from the pattern function Fθ (θ,φ) or Fφ(θ,φ),
versus either the angle θ (for an elevation plane pattern) or the angle φ (for an azimuthal plane
pattern). The choice of plotting either Fθ or Fφ is dependent on the polarization of the antenna.
10. Define Half Power Beam Width (HPBW) of an antenna.

Half Power Beam Width is a measure of directivity of an antenna. It is an angular width
in degrees, measured on the radiation pattern (main lobe) between points where the radiated
power has fallen to half its maximum value.

11. Define beam solid angle.

The beam area or beam solid angle  A for antenna is given by integral of the
normalized power pattern over a sphere.
2 
A =   P ( , ) d
0 0
n steradian
Pn ( ,  ) = Normalized power pattern

Beam solid angle is also given approximately by
 A =  HP  HP steradian
 HP = HPBW in E − plane or  plane
 HP = HPBW in H − plane or  plane
12. Define Beam Width between First Null.

Beam width between first null (BWFN) is the angular width in degrees, measured on
the radiation pattern between first null points on either side of the main lobe.
13. Define main lobe, side lobe, minor lobe and back lobe with reference to antenna
radiation pattern.
Major Lobe: Major lobe is also called as main beam and is defined as “the radiation lobe
containing the direction of maximum radiation”. In some antennas, there may be more than one
major lobe.
Minor lobe: All the lobes except the major lobes are called minor lobe.
Side lobe: A side lobe is adjacent to the main lobe.
Back lobe: Normally refers to a minor lobe that occupies the hemisphere in a direction opposite
to that of the major(main) lobe .
Minor lobes normally represents radiation in undesired directions and they should be minimized.

14. Define directivity of an antenna.

The directivity(D) of an antenna is defined as the ratio of the maximum value of the
power radiated per unit solid angle to the average power radiated per unit solid angle.
That is, directivity is ratio of the maximum radiation intensity in the main beam to the average
radiation intensity over all space.
𝑈𝑚𝑎𝑥 𝑈𝑚𝑎𝑥 4𝜋𝑈𝑚𝑎𝑥
𝐷= = = 2𝜋 𝜋
𝑈𝑎𝑣𝑔 𝑃𝑟𝑎𝑑⁄ 𝑈(𝜃, ∅)𝑠𝑖𝑛𝜃𝑑𝜃𝑑∅
4𝜋 ∫∅=0 ∫𝜃=0
Thus, the directivity measures how intensely the antenna radiates in its preferred direction than
an isotropic radiator would when fed with the same total power.
Directivity is a dimensionless ratio of power, and is usually expressed in dB as D(dB) = 10
log(D)
15. What do you mean by an isotropic radiator? What is the directivity of isotropic
radiator?
An isotropic radiator is a hypothetical loss less radiator having equal radiation in all
directions.
2𝜋 𝜋
U(θ,φ) = 1 for isotropic antenna. Applying the integral identity, ∫∅=0 ∫𝜃=0 𝑠𝑖𝑛𝜃𝑑𝜃𝑑∅ = 4𝜋, we
have,
4𝜋𝑈𝑚𝑎𝑥
𝐷 = 2𝜋 𝜋 =1
∫∅=0 ∫𝜃=0 𝑈(𝜃, ∅)𝑠𝑖𝑛𝜃𝑑𝜃𝑑∅
The directivity of an isotropic antenna is D = 1, or 0 dB.
16. What is the Relationship between Directivity and beamwidth?

Beamwidth and directivity are both measures of the focusing ability of an antenna. An antenna
pattern with a narrow main beam will have a high directivity, while a pattern with a wide beam
will have a lower directivity.
Approximate relation between beam width and directivity that apply with reasonable
accuracy for antennas with pencil beam patterns is the following:
32,000
𝐷≅ 𝜃𝜃 where θ1 and θ2 are the beam widths in two orthogonal planes of the main
1 2
beam, in degrees. This approximation does not work well for omnidirectional patterns because
there is a well-defined main beam in only one plane for such patterns.

17. Define omnidirectional antenna. Give its appliccations.
Antennas having a constant pattern in the azimuthal plane are called omnidirectional, and are
useful for applications such as broadcasting or for hand-held wireless devices, where it is desired
to transmit or receive equally in all directions.
18. Define pencil beam antenna and give its applications.

Antennas with radiation pattern that have relatively narrow main beams in both planes are
known as pencil beam antennas.
Pencil beam antenna are useful in applications such as radar and point-to-point radio links.
19. Define radiation efficiency of antenna.

Radiation efficiency of an antenna is defined as the ratio of the radiated output power to the
supplied input power.
𝑃𝑟𝑎𝑑 𝑃𝑖𝑛 − 𝑃𝑙𝑜𝑠𝑠 𝑃𝑙𝑜𝑠𝑠
𝜂𝑟𝑎𝑑 = = =1−
𝑃𝑖𝑛 𝑃𝑖𝑛 𝑃𝑖𝑛
where Prad is the power radiated by the antenna, Pin is the power supplied to the input of the
antenna, and Ploss is the power lost in the antenna(dissipative losses) due to metal conductivity
or dielectric loss with in the antenna.
20.Define gain of an antenna. What is the significance of gain of an antenna?

The gain of the antenna is closely related to the directivity, it is a measure that takes into account
the efficiency of the antenna as well as its directional capabilities.
Antenna gain is defined as the product of directivity and efficiency:
𝐺𝑎𝑖𝑛 = 𝐺 = 𝜂𝑟𝑎𝑑 × 𝐷.
Thus, gain is always less than or equal to directivity.
21. Define aperture efficiency.

Aperture efficiency is defined as the ratio of the actual directivity of an aperture antenna to the
maximum directivity of aperture antenna.
The maximum directivity that can be obtained from an electrically large aperture of area A is
4𝜋𝐴
given as, 𝐷𝑚𝑎𝑥 = 𝜆2
D
ηap = aperture efficieny =
Dmax
22.Define effective aperture area. What is the relation between effective aperture area and
Directivity(gain)?
Received power is proportional to the power density, or Poynting vector, of the incident wave.
Since the Poynting vector has dimensions of W/m2, and the received power, Pr, has dimensions
of W, the proportionality constant must have units of area.
We have, 𝑃𝑟 = 𝐴𝑒 × 𝑆𝑎𝑣𝑔
where Ae is defined as the effective aperture area of the receive antenna. The effective aperture
area has dimensions of m2, and can be interpreted as the “capture area” of a receive antenna,
intercepting part of the incident power density radiated toward the receive antenna.
The maximum effective aperture area of an antenna is related to the directivity of the antenna as,
𝐷𝜆2
𝐴𝑒 =
4𝜋
The maximum effective aperture area as defined above does not include the effect of losses in
the antenna, which can be accounted for by replacing D with G, the gain, of the antenna.

23.Define Antenna Brightness temperature
When the antenna beam width is broad enough that different parts of the antenna pattern see
different background temperatures, the effective brightness temperature seen by the antenna can
be found by weighting the spatial distribution of background temperature by the pattern function
of the antenna.
Mathematically we can write the brightness temperature Tb seen by the antenna as
2𝜋 𝜋
∫∅=0 ∫𝜃=0 𝑇𝐵 (𝜃, ∅)𝐷(𝜃, ∅)𝑠𝑖𝑛𝜃𝑑𝜃𝑑∅
𝑇𝑏 = 2𝜋 𝜋
∫∅=0 ∫𝜃=0 𝐷(𝜃, ∅)𝑠𝑖𝑛𝜃𝑑𝜃𝑑∅
Where 𝑇𝐵 (𝜃, ∅) is the distribution of the background temperature, and 𝐷(𝜃, ∅) is the
directivity (or the power pattern function) of the antenna. Antenna brightness temperature is
referenced at the terminals of the antenna. Observe that when TB is a constant, Tb = TB
24. What is the significance of G/T ratio?

Useful figure of merit for receive antennas is the G/T ratio, defined as 10 log( G/ TA) dB/K,
where G is the gain of the antenna, and TA is the antenna noise temperature.
This quantity is important because, the signal-to-noise ratio (SNR) at the input to a
receiver is proportional to G/TA. The ratio G/T can often be maximized by increasing the gain
of the antenna, since this increases the numerator and usually minimizes reception of noise from
hot sources at low elevation angles. Of course, higher gain requires a larger and more expensive
antenna, and high gain may not be desirable for applications requiring omnidirectional coverage
(e.g., cellular telephones or mobile data networks), so often a compromise must be made.
25.State why impedance matching(tuning) is important.

Impedance matching or tuning is important for the following reasons:
(i)Maximum power is delivered when the load is matched to the line (assuming the
generator is matched), and power loss in the feed line is minimized.
(ii)Impedance matching sensitive receiver components (antenna, low-noise amplifier,
etc.) may improve the signal-to-noise ratio of the system.
(iii)Impedance matching in a power distribution network (such as an antenna array feed
network) may reduce amplitude and phase errors.
26. Give the Friis radio link formula.

𝐺𝑟 𝑃𝑡 𝐺𝑡 𝜆2
𝑃𝑟 =
(4𝜋𝑟)2
Pr= Received power ( antenna matched) in W
Pt= power in to transmitting antenna in W
Aet= Effective aperture of transmitting antenna, m2
Aer= Effective aperture of Receiving antenna , m2
r=distance between transmitting and receiving antenna , m
λ= wave length, m
27.Define EIRP. What is the significance of this quantity?

The product Pt Gt is defined as the Effective Isotropic Radiated Power (EIRP).
EIRP = Pt Gt W
For a given frequency, range, and receiver antenna gain, the received power is proportional to
the EIRP of the transmitter and received power can only be increased by increasing the EIRP.
This can be done by increasing the transmit power, or the transmit antenna gain, or both.

28.Define path loss.
Path loss is the quantity that account for the free-space reduction in signal strength with distance
between the transmitter and receiver.
Path loss= Transmitted power- Received power=Pt - Pr
Assuming unity gain antennas, path loss is given as (using Friis formula)
4𝜋𝑟
𝑝𝑎𝑡ℎ 𝑙𝑜𝑠𝑠 (𝑑𝐵) = 20 𝑙𝑜𝑔 ( )
𝜆
29.Define link margin

In practical communications systems it is usually desired to have the received power level
greater than the threshold level required for the minimum acceptable quality of service (usually
expressed as the minimum carrier-to-noise ratio (CNR), or minimum SNR).
This design allowance for received power is referred to as the link margin, and can be
expressed as the difference between the design value of received power and the minimum
threshold value of receive power:
Link margin (dB) = LM = Pr − Pr(min) > 0, where all quantities are in dB.
Link margin should be a positive number; typical values may range from 3 to 20 dB.
Having a reasonable link margin provides a level of robustness to the system to account
for variables such as signal fading due to weather, movement of a mobile user, multipath
propagation problems, and other unpredictable effects that can degrade system performance.
30.Define fade margin.

Signal fading occur due to weather, movement of a mobile user, multipath propagation
problems, and other unpredictable effects that can degrade system performance and quality of
service. Link margin that is used to account for fading effects is sometimes referred to as fade
margin.
31.How link margin for a given communication system can be improved?

Link margin for a given communication system can be improved by increasing the
received power (by increasing transmit power or antenna gains), or by reducing the minimum
threshold power (by improving the design of the receiver, changing the modulation method, or
by other means)
32.What is point-to-point communication. Mention some of its application.

• In a point-to-point radio system a single transmitter communicates with a single receiver.
Such systems generally use high-gain antennas in fixed positions to maximize received
power and minimize interference with other radios that may be operating nearby in the
same frequency range.
• Point-to-point radios are typically used for satellite communications, dedicated data
communications by utility companies, and backhaul connection of cellular base stations
to a central switching office.
PART B - C401.1
1.Explain in detail, the physical concept of radiation. Illustrate with necessary diagrams, how
the electromagnetic fields guided within the transmission line and antenna, finally get
“detached” from the antenna to form a free-space wave.
2. Explain in detail the field regions of antenna. What is the significance of Fraunhofer zone?

3.Define and explain in detail the terms Gain, Directivity, beam width, Bandwidth and
Polarization of an antenna.
4.Define and describe the following parameters of an antenna:
(i)Radiation Pattern
(ii)Radiation intensity
(iii)Directivity
(iv)Effective aperture
5.Define and explain the significance of the following antenna parameters:
(i) Antenna brightness temperature
(ii) Antenna noise temperature
(iii) Antenna Efficiency
(iv)Half Power Beam width
6. (i)How are antennas classified based on radiation characterstics? Explain with an example,
the radiation pattern characteristics of omnidirectional antenna.
(ii)Explain in detail about:
1)Radiation pattern lobes 2) Aperture efficiency 3) Beam solid angle
7. (i)Derive FRIIS transmission formula.
(ii) A radio link has a 20 W transmitter connected to an antenna of 2.5 m 2 effective aperture
at 5 GHz. The receiving antenna has an effective aperture of 0.5m2 and is located at a 15 Km
line of sight distance from the transmitting antenna. Assuming lossless, matched antennas, find
the power delivered to the receiver. (Nov 2019)
8. Explain the various loss and gain terms considered in the microwave link budget. Also discuss
on the significance of link margin and fade margin of a communication system.
9.Define and explain the various parameters used to analyse the noise characteristics of a
microwave receiver.
10.Discuss on the noise analysis of a Microwave receiver front end, including antenna and
transmission line contributions.
UNIT - II RADIATION MECHANISMS AND DESIGN ASPECTS

PART A - C401.2
1.What is a resonant antenna?

• Resonant antennas are those which correspond to a resonant transmission line that is an
exact number of half wave length long and is open at both ends.
• These are unterminated antennas and are used for fixed frequency operation.
• In resonant antennas standing wave exists. i.e, forward wave (incident wave) and
backward wave (reflected wave) exists.
• The radiation patterns of resonant antenna are bidirectional due to incident and reflected
waves.
2. Compare the radiation pattern of resonant and non-resonant antenna.

Resonant antenna - bidirectional radiation pattern
Non-resonant antenna – unidirectional radiation pattern
3.What is a non-resonant antenna?

• Non- resonant antenna is also called as travelling wave antenna.

• Non-resonant antenna corresponds to a transmission line that is excited at one end,
terminated correctly at the other end.
• No reflected waves are produced and all the incident waves are absorbed.
• Waves travel only in one direction and hence only unidirectional radiation patterns are
produced.
• It is a wideband antenna and it is not sharply tuned to one frequency
4. State Huygen’s Principle. (May 18)

Huygens’ principle states that “each point on a primary wave front can be considered to
be a new source of a secondary spherical wave and that a secondary wave front can be
constructed as the envelope of these secondary spherical waves .”
5. State Babinet’s principle and how it gives rise to the concept of complementary antenna?
(May 2013) (Nov 17)
Babinet’s principle states that the sum of the field at a point behind a plane having a screen and
the field at the same point when a complimentary screen is substituted, is equal to the field at the
point when no screen is present. This principle can be applied to slot antenna analysis.
6. State uniqueness theorem (May 2012)

Uniqueness theorem states that, for a given set of sources and boundary conditions in a
lossy medium, the solution to Maxwell’s equations is unique.
7. What is field equivalence principle? (May 2014)

The field equivalence principle is based on the uniqueness theorem which states that “a field in
a lossy region is uniquely specified by the sources within the region plus the tangential
components of the electric field over the boundary, or the tangential components of the magnetic
field over the boundary, or the former over part of the boundary and the latter over the rest of
the boundary .”
8. Draw various types of Horn antenna.

Different types of horn antenna are: E-Plane sectoral horn, H-plane sectoral horn, Pyramidal
horn, Conical horn
9. Distinguish between sectorial horn and pyramidal horn.

• Horn antenna is a wave guide one end of which is flared out. In pyramidal horn, the
flaring is along E and H. It has the shape of a truncated pyramid.
• In sectoral horn, the flaring is along E or H. If flaring is along the direction of electric
field, it is called sectoral E-plane horn. If flaring is along the direction of magnetic field,
it is called sectoral H-plane horn.
10. The aperture dimensions of a pyramidal horn are 12x6 cm and operating at a frequency
of 10 GHz. Find the beam width and directivity. (May 2013)
Frequency = 10 GHz
3 108
= = 3 cm
10 109
d = 12 cm and w = 6 cm

Beam width : E = 56 = 140
d

H = 67 = 33.50
w
4.5wd
power gain = = 36 = 15.56 dB
2
7.5wd
Directivity = = 60
2
11. What are secondary antennas? Give two examples. (Nov 17)
Secondary antennas are one that needs a primary antenna to excite it. Eg: Reflector antenna,
Lens antenna.
12. What is a corner reflector?

A corner reflector is made up of two flat-plate reflectors joined together to form a corner.
The corner reflector is generally used in conjunction with a dipole or dipole array kept parallel
to the corner line. Corner reflector gives a higher directivity.
13.What is the main advantage of Cassegrain reflector configuration?

The main advantage is that the primary feed horn and the associated receiver or transmitter can
be located conveniently behind the main reflector.
• The necessity of running long transmission lines or waveguides is also eliminated.
• Since the horn feed is kept behind the main reflector, one can afford to have a much
larger aperture for the horn.
14. What is the main disadvantage of Cassegrain reflector configuration?

The main disadvantage of Cassegrain reflector configuration is the large aperture
blockage by the sub-reflector. Hence, Cassegrain reflector configuration is used only for very
large aperture antennas having gain greater than 40dB.
15.What is slot radiator? What is its operating principle?

When a slot in a large metallic plane is coupled to an R.F source, it behaves like a diploe
antenna mounted over a reflecting surface. The slot is coupled to a feed line in such a manner
that E-field lies along the short axis of the slot.
16. Write any two differences between slot antenna and its complementary dipole antenna.
(i) First, the electric and magnetic fields are interchanged. In case of the dipole antenna the
electric lines are horizontal while the magnetic lines form loops in the vertical plane. But in case
of slot antenna, the magnetic lines are horizontal and the electric lines are vertical. The electric
lines are built up across the narrow dimensions of the slot. As a result, the polarization of the
radiation produced by a horizontal slot is vertical and vertical slot is horizontal.
(ii) Second, the direction of the lines of electric and magnetic force abruptly reverse from one
side of the metal sheet to the other. In case of the dipole, the electric lines have the same direction
while the magnetic line forms continuous loops.
17.The impedance of an infinitesimally thin λ/2 antenna is 73+j42.5 Ω. Calculate the

terminal impedance of an infinitesimally thin λ/2 slot antenna.(Nov/Dec 2015)
𝜂0 2 (377)2 35532.25
𝑍𝑆 = = = = 363.52 − 𝑗 211.64 Ω
4𝑍𝐶 4(73 + 𝑗42.5) (73 + 𝑗42.5)
18.What is a microstrip antenna?

A microstrip patch antenna is an antenna consisting of a thin metallic patch etched on the
dielectric substrate using PCB technology. It is also referred as printed antenna. Its performance
depends on shape (can be square, rectangular, triangular, circular) and size.
19.What are the features of microstrip antennas? (Dec 2011) (May 2015)(Nov/Dec
2015)(April/May 2017)
• Micro strip antennas are low profile, conformable to planar and nonplanar surfaces,
simple and inexpensive to manufacture using modern printed-circuit technology,
mechanically robust when mounted on rigid surfaces, compatible with MMIC designs,
and when the particular patch shape and mode are selected, they are very versatile in
terms of resonant frequency, polarization, pattern, and impedance.
• In addition, by adding loads between the patch and the ground plane, such as pins and
varactor diodes, adaptive elements with variable resonant frequency, impedance,
polarization, and pattern can be designed.
20.What are the major operational disadvantages of microstrip antennas?

Major operational disadvantages of microstrip antennas are their low efficiency, low
power, high Q (sometimes in excess of 100), poor polarization purity, poor scan performance,
spurious feed radiation and very narrow frequency bandwidth.
21.List the different methods of feeding Microstrip antenna.

(i) microstrip line feed
(ii) coaxial probe feed
(iii) aperture coupling
(iv) proximity coupling
22. Define the bandwidth of an antenna.

The band width of antenna is defined as “The range of frequencies within which the
performance of the antenna, with respect to some characteristics [input impedance, beam, width,
polarization, side lobe level, gain etc.] confirms to a specified standard.
23.What is wide band antenna? Give an example.

Antennas which maintain certain required characteristics like gain, front to back ratio,
SWR, Polarization, input impedance and radiation pattern over wide range of frequencies are
called wide band or broad band antennas. Log periodic antenna is a broadband antenna.
24. State Rumsey principle on frequency independence.(April/May 2017)

Rumsey’s principle states that the impedance and radiation pattern properties of an antenna will
be frequency independent if the antenna shape is specified only in terms of angles.
Example: Planar log spiral antenna
25. What is LPDA?

LPDA is log periodic dipole array. It is unidirectional broadband, multi element, narrow
beam, frequency independent antenna that has impedance and radiation characteristics that are
regularly repetitive as a logarithmic function of frequency.
26. Why is log periodic antennas called so?

Log periodic antennas are called so, because, it is an array antenna which has structural
geometry such that its impedance and radiation characteristics are periodic with the logarithm of
the frequency.
PART B - C401.2
1. Derive the expression for the field quantities (E and H) for a small oscillation current element.
(May 2016)(Nov/Dec 2016)
2. Derive the expression for the field quantities radiated from a  / 2 dipole and prove that the
radiation resistance to be 73 Ohms. (May 2016)
3.(i) Compare uniform and tapered aperture antennas. Give examples.
(ii)With neat diagrams, explain parabolic reflector antenna and its Cassegrain feeding system.
(Nov 2019)
4.Discuss the principle working of Parabolic reflectors. Explain the various feed techniques their
relative merits and demerits. Discuss the role of f/d ratio in the parabolic reflectors (f- focal
length, D – diameter of reflector). (May 2019)
5.(i) Explain the radiation mechanism of Microstrip antenna.
(ii) Write short notes on Slot antenna. (Nov 2019) (Nov 17)
6.Design a 50 to 200 MHz log periodic dipole antenna for gain corresponds to scale factor 0.8
and space factor 0.15. Assume the gap spacing at the smallest dipole is 3.6 mm. (May 18)
7.Explain in detail about log periodic antennas. What is the need for feeding from end with
shorter dipoles and the need for transposing the lines? Also discuss the effects of decreasing α.
(Nov/Dec 2016)
8.Design a Log-Periodic dipole array with 7 dBi gain and a 4 to 1 bandwidth. Specify apex angle
α, scale constant k and the number of elements. (Nov/Dec 2015)
9.Explain the design procedure for the construction of log periodic antenna. (May 2016)
10.Explain the principle of operation of Log periodic antenna with neat schematic diagram.
(Nov/Dec 2016) (May 2019)
11.Discuss in detail how a spiral antenna behaves as a frequency independent antenna. (May
2014)
12.(i) What is Log periodic antenna? Explain the principle of Log periodic antenna.
(ii) Design a 50 – 200 MHz log – periodic antenna to obtain a gain corresponds to scale factor
0.8 and space factor 0.15(Nov 2019)
13.Explain in detail the radiation from a slot antenna and their feed systems. (Nov/Dec 2016)
14.(i) Explain the principle of parabolic reflector antenna and discuss on different types of feed
used with neat diagram.
(ii) The diameter of a parabolic reflector is 2m. For operation at 6GHz, find the beam width
between first nulls and the gain. (Nov 17)
15.Explain the principles of operation of Horn antenna and discuss the various forms of Horn
antenna. Obtain the design equations of Horn antenna. (May 18) (May 2019)
16.Explain the radiation mechanism of a microstrip antenna with suitable illustrations. With
suitable figures explain the various feed techniques. (May 18)
17.Explain the principle of operation and applications of loop antenna.
UNIT - III ANTENNA ARRAYS AND APPLICATIONS

PART A - C401.3
1. What is an antenna array?

• Antenna array is system of a similar antennas oriented similarly to get greater
directivity in a desired direction.
• Antenna array is a radiating system consisting of several spaced and properly phased
(current phase) radiators.
2.What is a Linear Array?

An antenna array is said to be linear if the individual antennas of the array are equally spaced
along a straight line.
3. Define uniform linear array.

Uniform linear array is defined as the one in which the elements are fed with a current
of equal amplitude (magnitude) with uniform progressive phase shift along the line. The
individual antennas of the array are equally spaced along a straight line.
4. Why we go for non-uniform amplitude distribution?

We go for non- uniform amplitude distribution to reduce side lobe levels.
5. Distinguish between uniform and non-uniform arrays.

• Uniform linear array is one in which the elements are fed with a current of equal
amplitude.
• Non-uniform linear array is one in which the elements are fed with currents of un equal
amplitude.
6. What is uniform Array?

An array of identical elements all of identical magnitude and each with a progressive
phase is referred to as a uniform array.
In other words, Uniform Array is an Array in which the array elements are fed with a
current of equal amplitude (magnitude) with uniform progressive phase shift along the line.
7.What are the factors that decide the radiation characteristics of array?
In an array of identical elements, there are at least five controls that can be used to shape the
overall pattern of the antenna.
These are:
1. the geometrical configuration of the overall array (linear, circular, rectangular, spherical, etc.)
2. the relative displacement between the elements
3. the excitation amplitude of the individual elements
4. the excitation phase of the individual elements
5. the relative pattern of the individual elements
8.Define Grating lobes

Lobes with maxima in other directions, in addition to the main maximum is referred to as Grating
lobes.
9.What is end-fire array?

End-fire array is defined as an array in which the principal radiation direction is along the
array axis. i.e., maximum radiation is along the axis of the array.
10.Give the condition to have only one end-fire maximum.

To have only one end-fire maximum and to avoid any grating lobes, the maximum spacing
between the elements should be less than half the wave length. i.e, dmax < λ/2.
11. What is broad-side array?

Broadside array is defined as an array in which the principal radiation direction is
perpendicular to the array axis.
12. A uniform linear array contains 50 isotropic radiators with an inter element spacing of
 / 2 . Find the directivity of broadside forms of arrays. (May 2013)
N=50 d=  / 2
Array length=N d=l = 25
l
Directivity of Broadside array = 2  =50

13. What is tapering of arrays? (May 2019)

The techniques used in reduction of side lobe level are called as tapering. It is found that minor
lobes are reduced if the center source radiates more strongly than the end sources (non-uniform
current distribution). Hence tapering is done from center to end according to some prescription.
14. What are the advantages of antenna arrays? (May 2014)

The advantages of antenna arrays are:
(i) It offers high directivity. Also, the directivity can be varied by choosing a proper
number of elements according to the need.
(ii) The strength of the transmitted signal significantly increased.
(iii)It offers beam steering electronically. Thus, the direction of the beam can be changed
from one point to another.
(iv) It provides a better signal to noise ratio.
(v) With the application of non-uniform input to each element, the radiation pattern can be
shaped according to the requirement.
(vi) The design of the antenna array supports better antenna performance.
15.Draw the radiation pattern for a linear array of two isotropic elements spaced λ/2 apart
and with equal current fed in phase. (April/May 2017) (May 2019)

Normalized total field of two element array of isotropic point sources of same amplitude and
same phase that are  / 2 apart is
 2  
  cos 
E nor = cos  2  = cos  cos 
 2  2 
 
 
16.Draw the radiation pattern of an isotropic point sources of same amplitude and opposite
phase that are  / 2 apart along X-axis symmetric with respect to origin. (May 2016)
Normalized total field of two element array of isotropic point sources of same amplitude and
opposite phase that are  / 2 apart is,
 2  
  cos 
E nor = sin   2  = sin   cos 
 2  2 
 
 
17. A uniform linear array of 4 isotropic elements with an inter element spacing of  / 2 .
Find the BWFN and directivity of end fire arrays.
n=4 , d=  / 2
Array length= nd =l = 2

2
BWFN = 2 =2
nd
l
Directivity of end fire array = 4  =8
 
18. How number of array elements effect directivity?

As number of array element increases; the beam width will be lesser and this will result
better directivity.
19. What is the advantage of pattern multiplication?

The advantage of pattern multiplication is it is a simple method for obtaining radiation pattern
of arrays which makes it possible to sketch rapidly, the radiation pattern of complicated arrays
without making lengthy calculations, almost by inspection.
20.State the principle of pattern multiplication

The field pattern of an array of non-isotropic but similar sources is the product of the pattern of
the individual source and the pattern of an array of isotropic point sources having the same
locations, relative amplitudes, and phase as the non- isotropic sources.
The total field pattern of an array of non-isotropic but similar sources is the product of
individual source pattern and the pattern of an array of isotropic point sources each located at
the phase center of the individual source and having the same relative amplitude and phase, while
the total phase pattern is the sum of the phase patterns of the individual source and the array of
isotropic point sources.
𝐸 = 𝑓(𝜃, 𝜑)𝐹(𝜃, 𝜑)∠ (𝑓𝑝 (𝜃, 𝜑) + 𝐹𝑝 (𝜃, 𝜑))
𝑓(𝜃, 𝜑)𝐹(𝜃, 𝜑) = 𝑓𝑖𝑒𝑙𝑑𝑝𝑎𝑡𝑡𝑒𝑟𝑛𝑜𝑓𝑎𝑟𝑟𝑎𝑦
(𝑓𝑝 (𝜃, 𝜑) + 𝐹𝑝 (𝜃, 𝜑)) = 𝑝ℎ𝑎𝑠𝑒𝑝𝑎𝑡𝑡𝑒𝑟𝑛𝑜𝑓𝑎𝑟𝑟𝑎𝑦
𝑓(𝜃, 𝜑) = 𝑓𝑖𝑒𝑙𝑑𝑝𝑎𝑡𝑡𝑒𝑟𝑛𝑜𝑓𝑖𝑛𝑑𝑖𝑣𝑖𝑑𝑢𝑎𝑙𝑠𝑜𝑢𝑟𝑐𝑒
𝑓𝑝 (𝜃, 𝜑) = 𝑝ℎ𝑎𝑠𝑒𝑝𝑎𝑡𝑡𝑒𝑟𝑛𝑜𝑓𝑖𝑛𝑑𝑖𝑣𝑖𝑑𝑢𝑎𝑙𝑠𝑜𝑢𝑟𝑐𝑒
𝐹(𝜃, 𝜑) = 𝑓𝑖𝑒𝑙𝑑𝑝𝑎𝑡𝑡𝑒𝑟𝑛𝑜𝑓𝑎𝑟𝑟𝑎𝑦𝑜𝑓𝑖𝑠𝑜𝑡𝑟𝑜𝑝𝑖𝑐𝑠𝑜𝑢𝑟𝑐𝑒𝑠
𝐹𝑝 (𝜃, 𝜑) = 𝑝ℎ𝑎𝑠𝑒𝑝𝑎𝑡𝑡𝑒𝑟𝑛𝑜𝑓𝑎𝑟𝑟𝑎𝑦𝑜𝑓𝑖𝑠𝑜𝑡𝑟𝑜𝑝𝑖𝑐𝑠𝑜𝑢𝑟𝑐𝑒𝑠
21.Using pattern multiplication find the radiation pattern for the broadside array of 4
elements, spacing between each element is λ/2.(April/May 2017)

22. What is the practical major disadvantage of Binomial array?

A major practical disadvantage of binomial arrays is the wide variations between the amplitudes
of the different elements of an array, especially for an array with a large number of elements.
This leads to very low efficiencies for the feed network, and it makes the method not very
desirable in practice.
For example, the relative amplitude coefficient of the end elements of a 10-element array is
1 while that of the center element is 126. Practically, it would be difficult to obtain and maintain
such large amplitude variations among the elements. They would also lead to very inefficient
antenna systems.
23.What is the main advantage of Binomial array?

Binomial arrays usually possess the smallest side lobes when compared to Dolph-Tschebyscheff
and uniform arrays. Binomial arrays with element spacing equal or less than λ/2 have no side
lobes.
The main advantage of Binomial array is the absence or no side lobes in the radiation
pattern of Binomial array when the element spacing is equal to or less than λ/2.
24. What is binomial array?

Binomial array is an array whose elements are excited according to the current
distribution determined by the coefficients of Binomial series.
Binomial series:

(1 + x )m−1 = 1 + (m − 1)x + (m − 1)(m − 2) x 2 + (m − 1)(m − 2)(m − 3) x 3 + ............

2! 3!
For example, For m =3
(1 + x )3−1 = 1 + (3 − 1)x + (3 − 1)(3 − 2) x 2 + (3 − 1)(3 − 2)(3 − 3) x 3 + ............
2! 3!
= 1 + 2x + x 2
Current distribution for 3 element binomial array is 1:2:1
25. What are the advantages of Dolph-Tschebyscheff array?

The advantages of Dolph-Tschebyscheff array are
• It provides a minimum beam width for a specified side lobe level.
• It provides pattern which contains side lobes of equal level.
• The amplitude distribution is not highly tapered and hence it is more practical.
26. What is Phased arrays ? (APR/MAY 18)

• In antenna theory, a phased array usually means an electronically scanned array; a
computer-controlled array of antennas which creates a beam of radio waves which can
be electronically steered to point in different directions, without moving the antennas.
• In an array antenna, the radio frequency current from the transmitter is fed to the
individual antennas with the correct phase relationship so that the radio waves from the
separate antennas add together to increase the radiation in a desired direction, while
cancelling to suppress radiation in undesired directions.
• In a phased array, the power from the transmitter is fed to the antennas through devices
called phase shifters, controlled by a computer system, which can alter the phase
electronically, thus steering the beam of radio waves to a different direction.
27.Define adaptive array(smart antennas).

• Adaptive arrays are antenna array that can steer the beam to any direction of interest
while simultaneously nulling interfering signals.
• Smart antennas (also known as adaptive array antennas, digital antenna arrays)
are antenna arrays with smart signal processing algorithms used to identify spatial signal
signatures such as the direction of arrival (DOA) of the signal, and use them to
calculate beamforming vectors which are used to track and locate the antenna beam on
the mobile/target.
• Smart antenna techniques are used notably in acoustic signal processing, track and
scan radar, radio astronomy and radio telescopes, and mostly in cellular systems like W-
CDMA, UMTS, and LTE.
• Smart antennas have many functions: DOA(Direction of Arrival) estimation,
beamforming, interference nulling, and constant modulus preservation.
PART B - C401.3
1. (i) Write a note on binomial array?

(ii) Draw the pattern of 10 element binomial array with spacing between the elements of 3 / 4
and  / 2 . (May 2013)
2. Derive the expressions for field pattern of broad side array of n point sources.(May 2013)(Nov
2019)

3. Two identical radiators are spaced d = 3 / 4 meters apart and fed with currents of equal
magnitude but with 1800 phase difference. Evaluate the resultant radiation and identify the
direction of maximum & minimum radiation. (May 2015)
4. For a 2 element linear antenna array separated by a distance d = 3 / 4 , derive the field
quantities and draw its radiation pattern for the phase difference of 450. (Dec 2012)
5. Derive the expressions for field pattern of end-fire array of n sources of equal amplitude and
spacing. (May 2012)
6. An antenna array consists of two identical isotropic radiators spaced by a distance of d=  / 4

meters and fed with currents of equal magnitude but with a phase difference  . Evaluate the
resultant radiation for  = 0 0 and thereby identify the direction of maximum radiation. (Dec
2011)
7. Describe a broadside array. Deduce an expression for the radiation pattern of a broadside array
with two point sources.
8. Plot the radiation pattern of a linear array of 4 isotropic elements spaced λ/2 apart and fed out
of phase with equal currents.
9.(i) Derive Array factor of an Uniform linear array of n sources. Explain the significance of
array factor. (Dec 2013)
(ii) Compare End fire and Broadside array. (May 2014)
10. Explain in detail about: 1) adaptive arrays 2) Phased arrays.(Nov 2019)
11.Obtain the expression for the field and the radiation pattern produced by a N element array
of infinitesimal with distance of separation  / 2 and currents of unequal magnitude and phase
shift 180 degree. (May 2016)
12. (i)Using pattern multiplication determine the radiation pattern for 8 element array separated
by the distance  / 2 .
(ii) Write short notes on tapered array and phased array. (May 2016)
13.Develop a treatise on the following forms of arrays: (Nov/Dec 2015)
(i)Linear array
(ii)Two-element array
(iii)Uniform array
(iv)Binomial array
14.Derive and draw the radiation pattern of 4 isotropic sources of equal amplitude and same
phase. (April/May 2017)(Nov/Dec 2016)
15.(i) Describe the principle of phased arrays and explain how it is used in beam forming.
(April/May 2017)(Nov/Dec 2016)
(ii)Write short notes on binomial arrays. (April/May 2017)(Nov/Dec 2016)
16.Derive the expression for the array factor of a linear array of four isotropic element spaced
λ/2 apart fed with signals of equal amplitude and phase. Obtain the directions of maxima and
minima.(Nov17)
17.(i) Explain in detail the Binomial array and derive the expression for the array factor. Also
obtain the excitation coefficients of a seven element binomial array.
(ii)What is phased array?(Nov 17)
18.Derive the expression for the array factor of a linear array of four isotropic element spaced
λ/2 apart fed with signals of equal amplitude and phase. Obtain the directions of maxima and
minima. (May 18)

19.Design a broadside Dolph-Tschebyscheff array of 10 elements with spacing‘d’ between the
elements and with a major-to-minor lobe ratio of 26 dB. Find the excitation coefficients and form
the array factor. (May 18)
UNIT - IV PASSIVE AND ACTIVE MICROWAVE DEVICES

PART A - C401.4
1. Define any two performance factors of directional couplers. List out the different types
of directional couplers.
The two performance factors of DC are the Coupling Factor and Directivity. Coupling Factor
defines the ratio of the amount of power coupled in coupled port to that of power at input port in
decibels. Directivity is defined as the ratio of powers at the isolated port and the incident ports
at decibels.
Types: Bethe hole DC, 2 hole, crossed guide DC, coupled line couplers, branch line couplers,
and Lange DC are the different types of directional couplers.
2. Name some uses of waveguide Tees. What are the two different types of waveguide Tees?
It is used to connect a branch or section of the waveguide in series or parallel with the main
waveguide transmission line for providing means of splitting and also of combining power in a
waveguide system.
Types: (i) E-plane tee (series) and (ii) H-plane tee (shunt).
3. Write the application of magic Tee. (Nov 2012 & May 2017)
Measurement of impedance, (ii) As duplexer (iii) As mixer and (iv) As an isolator.
4. What is hybrid ring or Rat-Race junctions? (May 2013)

The hybrid ring is a four-port junction .The four ports are connected in the form of an angular
ring at proper intervals by means of series (or parallel) junction. It also called Rat-race circuits.
It is mainly used to combining two signals (or) dividing a single signal into two equal halves.
5. What is negative resistance in Gunn diode? (May 2014)(Nov 2019)

The carrier drift velocity is linearly increased from zero to a maximum when the electric field is
varied from zero to a threshold value. When the electric field is beyond the threshold value of
3000v/cm, the drift velocity is decreased and the diode exhibits negative resistance. The diode
in the negative resistance will act as a source.
6. A Directional coupler is having coupling factor of 20dB and directivity of 40dB. If the
incident power is 900mW, what is the coupled power? (May 2013)
Coupling power (C) = 10log10 (Pi/Pf) =20 Pi/Pf =102 = 100 Therefore, Pf=Pi/100 = 9mW
Directivity (D) = 10log10 (Pf/Pb) = 40 Pf/Pb =104 = 1000 Therefore, Pb=Pf/1000 = 0.9MW
Coupled Power Pr =Pi-Pr-Pb = 90.1mW
7. What are the various materials used for Gunn diodes? What are the four different
modes of operation of GUNN diode?
GaAs, InP, CdTe, InAs are materials used in Gunn diode. Gunn oscillation mode, stable
amplification mode, LSA oscillation and bias current oscillation mode.
8. Mention the applications of IMPATT diode.

Microwave generators, Receiver local oscillators, parametric amplifier

9. What is Gunn Effect? (May 2013) (Nov 2014)

Above some critical voltage corresponding to an electric field of 2000-4000 v/cm the current in
every specimen became a fluctuating function of time. The frequency of oscillation was
determined mainly by the specimen and not by the external circuit. The length of the specimen
is inversely proportional to the frequency of oscillation. Some of materials like GaAs, InP, CdTe
exhibit a negative differential mobility when biased above a threshold value of the electric field.
10. Compare PIN and PN diode. (Nov 2016)

S.No PIN Diode PN Diode
1. A PIN diode is a diode with a wide, P-N junction diode is the most
undoped intrinsic semiconductor fundamental and the simplest
region between a p-type & an n-type electronics device.
semiconductor region.
2. The p-type and n-type regions are When one side of an intrinsic
typically heavily doped because they semiconductor is doped with acceptor
are used for ohmic contacts. i.e, one side is made p-type by doping
with n-type material; a p-n junction
diode is formed. This is a two terminal
device.
11. Draw the equivalent circuit of a Gunn diode.

The equivalent circuit of Gunn diode
Cj,Rj – Diode capacitance, Diode resistance

Rs- total resistance of lead ohmic contacts, bulk resistance
Cp,Lp – package capacitance and inductance
12. List out the different types of Magnetrons.

Negative Resistance magnetrons, Cyclotron frequency magnetron, Travelling wave magnetron
13. Explain Hull Cut-off condition.

Hull cut-off condition gives the cut-off magnetic field in a magnetron such that the electron
grazes the anode and returns back to the cathode.
14. What is the purpose of slow wave structures in TWT? Name them. (May 2018)
Slow wave structures are used to reduce the phase velocity of the wave in certain direction so
that the electron beam and signal wave can interact. Helical, Feedback line, Zig-Zag, Interdigital
line, corrugated wave guide.
15. List the advantages of Reflex klystron over multi-cavity klystrons.
Reflex klystrons can be used as an oscillator without any complex feedback circuitry as required
in multi-cavity klystrons. As it is a narrow bandwidth device it can be tuned to operate at a single
desired frequency in resonant circuits.
16. Explain the need for attenuators in TWT.

Attenuators are used to attenuate the unwanted signal traveling towards the input end due to
reflections arising from impedance mismatch.
17. What is meant by velocity modulation? (May 2018)

The change in the velocity of the electrons under the influence of an alternating field is termed
as velocity modulation
18. Define transit time in a Reflex klystron.

The time taken by electron to travel into the repeller space and come back toward the cavity is
called the transit time in Reflex klystron.
19. Bring out the differences between the TWT & Klystron (Nov 2013 & 2014)(May 2015
& 2017)
TWT Klystron
High BW Narrow BW
More gain Less gain
Use non-resonant structures Use cavity resonators
Continuous interaction between electron Discontinuous interaction between electron
beam and RF voltage beam and RF voltage
20. What do you meant by bunching?

The electrons traveling with different velocities join together at their transit towards the output
end. This collection of different velocity modulated electrons is called bunching
21. Define: Convection current of TWT (May 2014)

It is due Continuous interaction between the velocity and density modulations.
22. Write the application of Reflex klystron

Local oscillator in microwave receiver (ii) Microwave signal source (iii) pump oscillator for
parametric amplifier (iv) as an oscillator, in frequency modulation of low power microwave link.
23. What are the classifications of Microwave tubes and explain the difference between
them. (May 2017)
Linear beam tubes (O –type) Cross field tubes (M- type)
In O-Type tube , a magnetic field whose axis In M-Type tube, electric field is in the
coincides with the electron beam is used to radial direction & magnetic field is in the
hold the beam together as it travels the length axial direction.
of the tube
Reflex Klystron, TWT are Linear beam tubes Magnetron is M-type beam tubes
Low power device Low power device

24. Write the application of backward wave oscillator.
Signal source sources in instrument and transmitters. (2) Broad band noise source
Noise less oscillator with good bandwidth in frequency range 3-9 GHz.
25. Define Electronic Admittance.

It is defined by the ratio of induced bunch beam current and cavity gap voltage.
26. What is drift space?

The separation between buncher and catcher grids is called drift space.
27. What is magnetron? (NOV 2016)

Magnetron is an electron tube for amplifying or generating microwaves, with the flow of
electrons controlled by an external magnetic field.
28. What are Tetrodes and Pentodes? (NOV 2016)

Tetrodes and pentodes are called as vacuum tubes. A pentode is an electronic device having
five active electrodes. Tetrodes are a thermionic valve having four electrodes.
29. What do you mean by O type tube? Name some O type tubes.
In O-type tube a magnetic field whose axis coincides with the electron beam is used to hold the
beam together as it travels the length of the tube. It’s also called as linear beam tube. TYPES -
Helix travelling wave tube and coupled cavity TWT.
30. How to minimize the lead inductance and inter electrode capacitance. (NOV 2018)
The lead inductance and inter electrode capacitance minimized by reducing the lead length and
electrode area.
31. Distinguish between O-type and M-type tubes. (NOV 2018)

Sl.No. O Type tubes M Type tubes
1. Linear beam tube Crossed field tubes
2. DC magnetic field is in parallel with dc DC magnetic field and dc electric
electric field is used to focus the electrons field are perpendicular to each
beam. other
3. Electron receive potential energy from the dc Dc magnetic field plays a direct
beam voltage before they arrive in the role in the RF interaction process.
microwave interaction region and converted
into kinetic energy
Example: Klystron ,TWT Magnetron
PART B- C401.4
1. Explain how Directional coupler can be used to measure reflected power. Also Derive
scattering Matrix for Two hole Directional coupler. (Nov2012) (May 2013 & 2015) (Nov 2019)
2. Derive and explain the properties of H-plane tee and give reasons why it is called shunt Tee.
(Nov 2012) (May 2017)
3. Derive and explain the properties of E-plane tee and give reasons why it is called series Tee.
(Nov 2014) (Dec 2015) (May 2013) (May 2017)
4. (i)Derive the equation for scattering matrix of magic Tee.(Nov 2013) (Nov 2017)
(ii) Find the directivity in db for a coupler if the same power is applied in turn to input and output
of the coupler with output terminated in each case in matched impedance. The auxiliary output
readings are 450mW and 0.710µW. (May 2014)
5. Explain the working of Attenuators with neat diagram. (May 2014)(Dec 2015)
6. Explain Physical structure, negative resistance, power output & efficiency of IMPATT Diode.
(Nov 2013) (May 2013) (Dec 2015) (May 2015)
7. Briefly Explain Gunn Effect & modes of operation of the Gunn Diode. Explain the working
principle of Gunn diode with two valley model and plot its characteristics. (Dec 2015) (May
2015) (Nov 2019)
8. Derive the S matrix for a directional coupler and also verifying the properties of it (May 2018)
9. (i)Derive the S matrix H plane TEE.
(ii)Explain the mode of oscillation of gunn diode. . (May 2018)
10. (i)Explain the construction of Magic Tee and derive its S-matrix.(Nov 2019)
(ii) Derive the scattering matrix for a directional coupler. (Nov 2018)
11. Describe the Gunn effect with the aid of two valley model theory
12. Explain the working principle and operation of multi-cavity Klystron amplifier and derive
the expression for its output power. (Nov 2016)
13. Explain the working principle of Reflex klystron oscillator and derive output power &
Efficiency. (Nov 2013) (Dec 2015) (Nov 2017)
14. Explain the operation of TWT Amplifier & write its characteristics. (Dec 2015) (Nov &
May 2017)
15. Explain π mode of operation of Magnetron Oscillators mention few high frequency
limitations. (May 2015)
16. A Reflex klystron is to be operated at frequency of 10 GHz, with dc beam voltage 300V,
3
repeller space 0.1 cm for 1 mode. Calculate PRFmax and corresponding repeller voltage for a
4
beam current of 20 mA.
17. A Reflex klystron is to be operated at frequency of 9 GHz, with dc beam voltage 600V,
3
repeller space 1 cm for 1 mode. Calculate electronic efficiency, output power and
4
corresponding repeller voltage for a beam current of 10 mA. The beam coupling coefficient is
assumed to be 1.
18. A two-cavity klystron amplifier is tuned at 3 GHz. The drift space length is 2cm and beam
current is 25mA. The catcher voltage is 0.3 times the beam voltage. It is assumed that the gap
length of the cavity << the drift space so that the input and output voltages are in phase (β = 1).
1
Compute (a) Power output and efficiency for N= 5 (b) Beam voltage, input voltage and output
4
1
voltage for maximum power output of N= 5 mode.
4
19. A two-cavity klystron amplifier operates at 5GHz with a dc beam voltage of 10KV and a 2
mm cavity gap. For a given input RF voltage, the magnitude of the gap voltage is 100 volts.
Calculate the transit time at the cavity gap, the transit angle, and the velocity of the electrons
leaving the gap.
20. An X- band pulsed conventional magnetron has the following operating parameters: Anode
Voltage Vo = 5.5 KV, Beam current is 4.5 mA, Operating frequency 9GHz, Resonator
conductance 2×10-4 mho, Loaded conductance 2.5 ×10-4 mho, Vane capacitance is 2.5 PF, Duty
cycle 0.002, Power loss is 18.5 KW. Compute 1) Angular resonant frequency, 2) Unloaded
quality factor 3) loaded quality factor, 4) external quality factor 5) circuit efficiency 6) electronic
efficiency
21. A 250kw pulsed cylindrical magnetron has the following parameters. Anode voltage =
25Kv, peak anode current = 25 A, Magnetic field = 0.35Wb/m2, Radius of the cathode = 4CM,
Radius of the Anode = 8CM, Calculate efficiency of the magnetron, cyclotron angular frequency,
Cutoff magnetic field. (May 2013)
22. Write a detailed note on cylindrical magnetron (Nov 2013) (Nov 2017)(Nov 2019)
23. A traveling wave tube (TWT) operates under the following parameters: Beam Voltage
V0=3Kv; Beam Current I0=30ma; Characteristics impedance of helix =Z0=10Ω; Circuit length
=N=50m; Frequency f=10GHz. Determine: (i) gain parameters C (ii) Output power gain Ap in
decibels. (iii) All four propagation constants. (Nov 2016)
24. With neat diagram explain the operation of two cavity Klystron amplifier and derive the
equations for velocity modulation process. (May 2017)(Nov 2019)
25. (i) Draw a neat sketch showing the constructional features of a cavity magnetron and explain
why magnetron is called as crossed field device. (ii) Derive an expression for cut off magnetic
field for a cylindrical magnetron. . (May 2018) (Nov 2019)
26. A reflex klystron is operated at 8 GHz with dc beam voltage of 600 V for 1.75 mode, repeller
space length of 1mm, and dc beam current of 9 mA. The beam coupling coefficient assumed to
be 1. Calculate the repeller voltage, electronic efficiency and output power.
Vo =600 V, L= 1mm,IO =9mA Β0 = 1, f=8 GHz, n =2 or 13/4 mode. (May 2018)
27. (i) Draw the schematic of two cavity Klystron amplifier and explain the process of velocity
modulation and bunching .Also derive the equation of velocity modulation.
(ii) With neat diagram, explain how amplification of RF wave is accomplished in Helix type
TWT. (Nov 2018)
28. (i)Draw the cross sectional view of Magnetron tube and explain the process of bunching.
Derive the expression for Hull cut off voltage. (ii) Compare TWT and Klystron(Nov 2018)
29. A two cavity Klystron amplifier has the following specifications.
Beam Voltage Vo= 900V
Beam current Io=30mA
Frequency f= 8 GHz.
Gap spacing in either cavity d= 1mm
Spacing between center of cavities L= 4cm
Effective shunt impedance Rth = 49kΩ
Determine
(i)Electron velocity(ii) Dc transit time of electron (iii)Maximum input voltage (iv)Voltage
gain(Nov 2018)
UNIT – V MICROWAVE DESIGN PRINCIPLES

PART A - C401.5
1. What do you mean by impedance matching? (May 2018)

The basic idea of impedance matching is illustrated in the following figure, which shows an
impedance matching network placed between a load impedance and a transmission line. The
matching network is ideally lossless, to avoid unnecessary loss of power, and is usually designed
so that the impedance seen looking into the matching network is Z0. Then reflections will be
eliminated on the transmission line to the left of the matching network, although there will
usually be multiple reflections between the matching network and the load. This procedure is
sometimes referred to as tuning.

2. Why impedance matching is significant in a microwave system? (May 2015)
▪ Maximum power is delivered when the load is matched to the line (assuming the
generator is matched), and power loss in the feed line is minimized.
▪ Impedance matching sensitive receiver components (antenna, low-noise amplifier, etc.)
may improve the signal-to-noise ratio of the system.
▪ Impedance matching in a power distribution network (such as an antenna array feed
network) may reduce amplitude and phase errors.
3. List out the factors that may be important in the selection of a particular matching
network? (Nov 2019)
Complexity, Bandwidth, Implementation and Adjustability
4. Define a filter.
A filter is a two-port network used to control the frequency response at a certain point in an RF
or microwave system by providing transmission at frequencies within the passband of the filter
and attenuation in the stopband of the filter. Typical frequency responses include low-pass, high-
pass, bandpass, and band-reject characteristics. Applications can be found in virtually any type
of RF or microwave communication, radar, or test and measurement system.
5. Differentiate between Image parameter and Insertion loss methods used in filter design.
Image parameter Method Insertion loss Method
Filters designed using the image parameter A more modern procedure, called the
method consist of a cascade of simpler two insertion loss method, uses network
port filter sections to provide the desired synthesis techniques to design filters with a
cutoff frequencies and attenuation completely specified frequency response.
characteristics but do not allow the
specification of a particular frequency
response over the complete operating range.
Thus, although the procedure is relatively The design is simplified by beginning with
simple, the design of filters by the image low-pass filter prototypes that are
parameter method often must be iterated normalized in terms of impedance and
many times to achieve the desired results. frequency. Transformations are then applied
to convert the prototype designs to the
desired frequency range and impedance
level.
6. What are called constant k filters?

If Z1 and Z2 of a reactance network are unlike reactance arms, then Z1Z2 = k2 where k is a
constant independent of frequency. Networks or filter sections for which this relation holds
are called constant-k filters.
7. Sketch low-pass constant-k filter sections in T and 𝝅 forms.

8. Sketch high-pass constant-k filter sections in T and 𝝅 forms.
9. Sketch m-Derived filters: Low-pass and High-pass T-sections.
10. What are the demerits of constant – k filters?

There are two major demerits in the constant – k filters. They are,
1.The attenuation does not rise very rapidly at cutoff, so that frequencies just outside the pass
band are not appreciably attenuated with respect to frequencies just inside the pass band. (a
relatively slow attenuation rate past cutoff)
2. The characteristic impedance varies widely over the pass band, so that a satisfactory
impedance match is not possible.( a nonconstant image impedance)
11. What are composite filters?

By combining in cascade the constant-k, m-derived sharp cutoff and the m-derived matching
sections we can realize a filter with the desired attenuation and matching properties. This type
of design is called a composite filter. The sharp-cutoff section, with m < 0.6, places an
attenuation pole near the cutoff frequency to provide a sharp attenuation response; the constant-
k section provides high attenuation further into the stopband. The bisected-π sections at the ends
of the filter match the nominal source and load impedance, R0, to the internal image impedances,
ZiT , of the constant-k and m-derived sections.
12. What are the steps involved in the process of filter design by the insertion loss method?
The design of low-pass filter prototypes that are normalized in terms of impedance and
frequency; this normalization simplifies the design of filters for arbitrary frequency, impedance,
and type (low-pass, high-pass, bandpass, or bandstop). The low-pass prototypes are then scaled
to the desired frequency and impedance, and the lumped-element components replaced with
distributed circuit elements for implementation at microwave frequencies.

13. Summarize the Prototype Filter Transformations.
14. Write about microwave filter implementation.

The lumped-element filter designs generally work well at low frequencies, but two problems
arise at higher RF and microwave frequencies. First, lumped-element inductors and capacitors
are generally available only for a limited range of values, and can be difficult to implement at
microwave frequencies. Distributed elements, such as open-circuited or short-circuited
transmission line stubs, are often used to approximate ideal lumped elements. In addition, at
microwave frequencies the distances between filter components is not negligible. The first
problem is treated with Richards’ transformation, which can be used to convert lumped elements
to transmission line sections. Kuroda’s identities can then be used to physically separate filter
elements by using transmission line sections. Because such additional transmission line sections
do not affect the filter response, this type of design is called redundant filter synthesis. It is
possible to design microwave filters that take advantage of these sections to improve the filter
response; such nonredundant synthesis does not have a lumped-element counterpart.
15. State the principle behind Richards’ transformation.

Richards’ transformation allows the inductors and capacitors of a lumped-element filter to be
replaced with short-circuited and open-circuited transmission line stubs, as illustrated in
following figure. Since the electrical lengths of all the stubs are the same (λ/8 at ωc), these lines
are called commensurate lines.
16. What is the role of Kuroda’s Identities in filter implementation?

The four Kuroda identities use redundant transmission line sections to achieve a more practical
microwave filter implementation by performing any of the following operations:
i) Physically separate transmission line stubs
ii) Transform series stubs into shunt stubs, or vice versa
iii) Change impractical characteristic impedances into more realizable values
17. Sketch Richard’s transformation
18. Sketch the four Kuroda Identities.

19. Mention the significance of Microwave transistor amplifiers.
Most RF and microwave amplifiers today use transistor devices such as Si BJTs, GaAs or SiGe
HBTs, Si MOSFETs, GaAs MESFETs, or GaAs or GaN HEMTs. Microwave transistor
amplifiers are rugged, low-cost, and reliable and can be easily integrated in both hybrid and
monolithic integrated circuitry. Transistor amplifiers can be used at frequencies in excess of 100
GHz in a wide range of applications requiring small size, low noise figure, broad bandwidth, and
medium to high power capacity. Although microwave tubes are still useful for very high power
and/or very high frequency applications, continuing improvement in the performance of
microwave transistors is steadily reducing the need for microwave tubes.
20. List out the usual microwave amplifier design goals.

i.Maximum power gain.
ii.Minimum noise figure for the first stage.
iii.Stable gain, i.e., no oscillations.
iv.Input and Output VSWR as close to unity as possible.
v.Adequate gain and uniformity of gain over a specified frequency band.
vi.Phase response that is a linear function of 𝜔 (no distortion, only group delay).
vii.Insensitivity to nominal changes or variations in the device Sij parameters.
21. Define Power gain.

Power gain = G = PL/Pin is the ratio of power dissipated in the load ZL to the power delivered to
the input of the two-port network. This gain is independent of ZS, although the characteristics of
some active devices may be dependent on ZS.
22. Define Available power gain. (Dec 2015)

Available power gain = GA = Pavn/Pavs is the ratio of the power available from the two-port
network to the power available from the source. This assumes conjugate matching of both the
source and the load, and depends on ZS, but not ZL.
23. Define Transducer power gain. (Nov 2013 & May 2017)
Transducer power gain = GT = PL/Pavs is the ratio of the power delivered to the load to the power
available from the source. This depends on both ZS and ZL.
24. State the conditions that are necessary and sufficient for unconditional stability.(May
2019)
In K-Δ test, it can be shown that a device will be unconditionally stable if Rollet’s condition,
defined as
1 − |𝑆11 |2 − |𝑆22 |2 + |Δ|2
𝐾= >1
2|𝑆12 𝑆21 |
along with the auxiliary condition that
|Δ| = |𝑆11 𝑆22 − 𝑆12 𝑆21 | < 1
are simultaneously satisfied.
25. What is the idea behind LNA design?

Besides stability and gain, another important design consideration for a microwave amplifier
is its noise figure. In receiver applications especially it is often required to have a preamplifier
with as low a noise figure as possible since the first stage of a receiver front end has the dominant
effect on the noise performance of the overall system. Generally, it is not possible to obtain both
minimum noise figure and maximum gain for an amplifier, so some sort of compromise must be
made. This can be done by using constant-gain circles and circles of constant noise figure to
select a usable trade-off between noise figure and gain.
26. Define noise figure.

Noise figure of the component is a measure of the degradation in the signal-to-noise ratio
between the input and output of the component. The signal-to-noise ratio is the ratio of desired
signal power to undesired noise power, and so is dependent on the signal power. When noise and
a desired signal are applied to the input of a noiseless network, both noise and signal will be
attenuated or amplified by the same factor, so that the signal-to-noise ratio will be unchanged.
However, if the network is noisy, the output noise power will be increased more than the output
signal power, so that the output signal-to-noise ratio will be reduced. The noise figure, F, is a
measure of this reduction in signal-to-noise ratio, and is defined as
𝑆𝑖
𝑠𝑖𝑔𝑛𝑎𝑙 − 𝑡𝑜 − 𝑛𝑜𝑖𝑠𝑒 𝑟𝑎𝑡𝑖𝑜 𝑎𝑡 𝑖𝑛𝑝𝑢𝑡 ⁄𝑁
𝑖
𝐹= = ≥1
𝑠𝑖𝑔𝑛𝑎𝑙 − 𝑡𝑜 − 𝑛𝑜𝑖𝑠𝑒 𝑟𝑎𝑡𝑖𝑜 𝑎𝑡 𝑜𝑢𝑡𝑝𝑢𝑡 𝑆0⁄
𝑁𝑜
where Si , Ni are the input signal and noise powers, and So, No are the output signal and noise
powers.
27. Give the noise figure expression for a cascaded system.

𝐹2 − 1 𝐹3 − 1
𝐹𝑐𝑎𝑠 = 𝐹1 + + +⋯
𝐺1 𝐺1 𝐺2
28. What is role of power amplifiers in transmitters?

Power amplifiers are used in the final stages of radar and radio transmitters to increase the
radiated power level. Typical output powers may be on the order of 100–500 mW for mobile
voice or data communications systems, or in the range of 1–100 W for radar or fixed-point radio
systems.
29. List out the types and characteristics of power amplifiers.

▪ Class A amplifiers are inherently linear circuits, where the transistor is biased to conduct
over the entire range of the input signal cycle. Because of this, class A amplifiers have a
theoretical maximum efficiency of 50%. Most small-signal and low-noise amplifiers
operate as class A circuits.
▪ In contrast, the transistor in a class B amplifier is biased to conduct only during one-half
of the input signal cycle. Usually two complementary transistors are operated in a class
B push-pull amplifier to provide amplification over the entire cycle. The theoretical
efficiency of a class B amplifier is 78%.
▪ Class C amplifiers are operated with the transistor near cutoff for more than half of the
input signal cycle, and generally use a resonant circuit in the output stage to recover the
fundamental. Class C amplifiers can achieve efficiencies near 100% but can only be used
with constant envelope modulations.
▪ Higher classes, such as class D, E, F, and S, use the transistor as a switch to pump a
highly resonant tank circuit, and may achieve very high efficiencies

30. Define a mixer.
A mixer is a three-port device that uses a nonlinear or time-varying element to achieve frequency
conversion. An ideal mixer produces an output consisting of the sum and difference frequencies
of its two input signals. Operation of practical RF and microwave mixers is usually based on the
nonlinearity provided by either a diode or a transistor. As we have seen, a nonlinear component
can generate a wide variety of harmonics and other products of input frequencies, so filtering
must be used to select the desired frequency components.
31. The IS-54 digital cellular telephone system uses a receive frequency band of 869– 894
MHz, with a first IF frequency of 87 MHz and a channel bandwidth of 30 kHz. What are
the two possible ranges for the LO frequency? If the upper LO frequency range is used,
determine the image frequency range. Does the image frequency fall within the receive
passband?
The two possible LO frequency ranges are
fLO = fRF ± fIF = (869 to 894) ± 87 =956 to 981 MHz and 782 to 807 MHz
Using the 956–981 MHz LO, we find that the IF frequency is
fIF = fRF − fLO = (869 to 894) − (956 to 981) = −87 MHz,
The RF image frequency range is
fIM = fLO − fIF = (956 to 981) + 87 = 1043 to 1068 MHz,
which is well outside the receive passband
32. Define conversion loss in a mixer.

Conversion Loss (CL) of a mixer is generally defined in dB as the ratio of supplied input power
PRF over the obtained IF power PIF. When dealing with BJTs and FETs, it is preferable to specify
a conversion gain (CG) defined as the inverse of the power ratio.
𝑃𝑅𝐹
CL = 10log ( )
𝑃𝐼𝐹
33. How are oscillators designed for microwave frequencies?

A solid-state oscillator uses an active nonlinear device, such as a diode or transistor, in
conjunction with a passive circuit to convert DC to a sinusoidal steady-state RF signal. Basic
transistor oscillator circuits can generally be used at low frequencies, often with crystal
resonators to provide improved frequency stability and low noise performance. At higher
frequencies, diodes or transistors biased to a negative resistance operating point can be used with
cavity, transmission line, or dielectric resonators to produce fundamental frequency oscillations
up to 100 GHz. Alternatively, frequency multipliers, in conjunction with a lower frequency
source, can be used to produce power at millimeter wave frequencies.
34. Compare and contrast diode-based and transistor-based oscillators.

Transistor oscillators generally have lower frequency and power capabilities than diode sources
(e.g., tunnel, Gunn, or IMPATT diodes), but offer several advantages over diodes. First,
oscillators using transistors are readily compatible with monolithic integrated circuitry, allowing
easy integration with transistor amplifiers and mixers, while diode devices are often less
compatible. In addition, a transistor oscillator circuit is much more flexible than a diode source.
This is because the negative resistance oscillation mechanism of a diode is determined and
limited by the physical characteristics of the device itself, while the operating characteristics of
a transistor can be adjusted to a greater degree by the bias point, as well as the source or load
impedances presented to the device. Transistor oscillators usually allow more control of the
frequency of oscillation, temperature stability, and output noise than do diode sources. Transistor
oscillator circuits also lend themselves well to frequency tuning, phase or injection locking, and
various modulation requirements. Transistor sources are relatively efficient but usually are not
capable of very high-power outputs.
35. Why is it necessary to go for microstrip line matching networks? (Nov 2018)
Design of matching networks involves discrete components. However, with increasing
frequency and correspondingly reduced wavelength, the influence of parasitics in the discrete
elements become more noticeable. The design now requires us to take these parasitics into
account, thus significantly complicating the component values computation. This, along with the
fact that discrete components are only available for certain values, limits their use in high
frequency circuit applications. As an alternative to lumped elements, distributed components are
widely used when the wavelength becomes sufficiently small compared with the characteristic
circuit component length.
PART B- C401.5
1. What is a matching network? Why is this required? Briefly explain T &π matching networks.
(Nov 2012& 2013)
2. Explain in detail about Microstrip line matching network with neat diagram. (May 2017)
3. Discuss the smith chart approach to design the L section and T section matching networks.
4. i)Explain the significance of impedance matching and tuning. ii) What are the design issues
in T and Pi matching network and explain. (Nov 2019)
5. Design an L-section matching network to match a series RC load with an impedance
ZL= (200-j100) Ω to 100Ω line at frequency of 500 MHz. (use smith chart).
6. Design a matching network to match a ZL= (10+j10) Ω to 50Ω line. Specify the values of L
and C at frequency of 1GHz. (use smith chart). (May 2014)
7. Using smith chart design any two possible configurations of discrete two element matching
networks to match the source impedance Zs= (50+j25) Ω to the load ZL = (25-j50) Ω. Assume
Zo= 50Ω, f=2GHz. (May 2015)
8. For a broadband amplifier, it is required to develop a Pi-type matching network that
transforms a load impedance of 𝑍𝐿 = (10 − 𝑗10) Ω into an input impedance 𝑍𝑖𝑛 = (20 +
𝑗40)Ω. The design should involve the lowest possible nodal quality factor. Find the component
values, assuming that matching should be achieved at a frequency of 𝑓 = 2.4 GHz .
9. Design a T-type matching network that transforms a load impedance 𝑍𝐿 = 60 − 𝑗30Ω into a
𝑍𝑖𝑛 = 10 + 𝑗20Ω input impedance and that has a maximum nodal quality factor of 3. Compute
the values for the matching network components, assuming that matching is required at
𝑓 = 1GHz.
10. Design a low-pass composite filter with a cutoff frequency of 2 MHz and impedance of
75 Ω. Place the infinite attenuation pole at 2.05 MHz, and plot the frequency response from 0 to
4 MHz.
11. Tabulate all the four Kuroda’s Identities and prove them.
12. Design a low pass filter for fabrication using microstrip lines. The specifications include a
cut-off frequency of 4 GHz, an impedance of 50Ω, and a third-order 3 dB equal-ripple
passband response. The normalized low-pass prototype element values are 𝑔1 = 3.3487 ; 𝑔2 =
0.7117 ; 𝑔3 = 3.3487 ; 𝑔4 = 1
13. Design a low pass filter whose input and output are matched to a 50Ω impedance and that
meets the following specifications: cut-off frequency of 3GHz; equi-ripple of 0.5dB; and
rejection of at least 40dB at approximately twice the cut-off frequency. Assume a dielectric
material that results in phase velocity of 60% of the speed of light. The filter coefficients are
𝑔1 = 𝑔5 = 1.7058 ; 𝑔2 = 𝑔4 = 1.2296 ; 𝑔3 = 2.5408 ; 𝑔6 = 1
14. Discuss in detail the steps involved in microwave filter design.
15. (i)Write mathematical analysis of amplifier stability (Nov/Dec 2018, April/May 2019) (ii)A
microwave amplifier is characterized by its S parameters. Derive equations for power gain,
available gain and transducer gain. (Nov 2012) (May 2015) (Nov 2016) (Nov 2018) (May 2018)
( May 2019) (Nov 2019)
16. An RF Amplifier has the following S-parameters: 𝑆11 = 0.3∠−700 , 𝑆12 =
0.2∠−100 , 𝑆21 = 3.5∠850 𝑎𝑛𝑑 𝑆22 = 0.4∠−450 . Furthermore, the input side of the amplifier
is connected to a voltage source with 𝑉𝑆 = 5𝑉∠00 and source impedance 𝑍𝑆 = 40Ω. The output
is utilized to drive an antenna which has an impedance of 𝑍𝐿 = 73Ω. Assuming that the S-
parameters of the amplifier are measured with reference to a 𝑍0 = 50Ω characteristic impedance,
find the following quantities: (a) Transducer gain 𝐺𝑇 , Unilateral transducer gain 𝐺𝑇𝑈 , available
gain 𝐺𝐴 , operating power gain G and (b) Power delivered to the load 𝑃𝐿 , available power 𝑃𝐴 and
incident power to the amplifier 𝑃𝑖𝑛𝑐 . (Nov 2017) (Nov 2019)
17. Investigate the stability regions of a transistor whose S-parameters are recorded as follows:
S12=0.2 ∟-10˚;S11=0.7∟ -70 ˚;S21=5.5 ∟85 ˚;S22=0.7∟ -45 ˚; at 750 MHz. (Nov 2016)
18. Explain in detail noise figure in an amplifier.
19. Discuss in brief steps involved in the design of Low Noise Amplifiers.
20. Elaborate on Microwave Power amplifiers and their efficiencies.
21. Explain in detail the types of mixers in microwave circuits.
22. Write a detailed note on microwave oscillator design.

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EC8701- Antennas and Microwave Engineering Department of ECE 2020-2021

EC8701 ANTENNAS AND MICROWAVE ENGINEERING L T P C

UNIT I INTRODUCTION TO MICROWAVE SYSTEMS AND ANTENNAS 9

St. Joseph’s College of Engineering / St. Joseph’s Institute of Technology 1

MAPPING BETWEEN CO AND PO, PSO WITH CORRELATION LEVEL 1/2/3

UNIT- I INTRODUCTION TO MICROWAVE SYSTEMS AND ANTENNAS

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3. List the conditions under which wire radiates.

4.Define reactive near field region of antenna.

5. Define radiating near field region( Fresnel region) of antenna.

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6. Define far field( Fraunhofer) region of antenna

8. Define Radiation Intensity. What is it’s significance?

𝑃𝑟𝑎𝑑 = 𝑃𝑜𝑤𝑒𝑟 𝑟𝑎𝑑𝑖𝑎𝑡𝑒𝑑 = ∫ ∫ 𝑈(𝜃, ∅)𝑠𝑖𝑛𝜃𝑑𝜃𝑑∅

9. Define Radiation pattern.

10. Define Half Power Beam Width (HPBW) of an antenna.

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11. Define beam solid angle.

Pn ( ,  ) = Normalized power pattern

12. Define Beam Width between First Null.

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14. Define directivity of an antenna.

16. What is the Relationship between Directivity and beamwidth?

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18. Define pencil beam antenna and give its applications.

19. Define radiation efficiency of antenna.

20.Define gain of an antenna. What is the significance of gain of an antenna?

21. Define aperture efficiency.

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24. What is the significance of G/T ratio?

25.State why impedance matching(tuning) is important.

26. Give the Friis radio link formula.

27.Define EIRP. What is the significance of this quantity?

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29.Define link margin

30.Define fade margin.

31.How link margin for a given communication system can be improved?

32.What is point-to-point communication. Mention some of its application.

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UNIT - II RADIATION MECHANISMS AND DESIGN ASPECTS

1.What is a resonant antenna?

2. Compare the radiation pattern of resonant and non-resonant antenna.

3.What is a non-resonant antenna?

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4. State Huygen’s Principle. (May 18)

6. State uniqueness theorem (May 2012)

7. What is field equivalence principle? (May 2014)

8. Draw various types of Horn antenna.

9. Distinguish between sectorial horn and pyramidal horn.

12. What is a corner reflector?

13.What is the main advantage of Cassegrain reflector configuration?

14. What is the main disadvantage of Cassegrain reflector configuration?

15.What is slot radiator? What is its operating principle?

17.The impedance of an infinitesimally thin λ/2 antenna is 73+j42.5 Ω. Calculate the

18.What is a microstrip antenna?

20.What are the major operational disadvantages of microstrip antennas?

21.List the different methods of feeding Microstrip antenna.

22. Define the bandwidth of an antenna.

23.What is wide band antenna? Give an example.

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