Basic Antenna Theory &

Communications Antenna
System

ComeC 513 2013
Agenda
Antenna definition
Antenna theory
Antenna parameters
Types of Antenna
Applications
Introduction
An ANTENNA is a conductor, or system of
conductors, that radiates or receives energy in
the form of electromagnetic waves.

Transmission - radiates electromagnetic energy into
space
Reception - collects electromagnetic energy from
space

The antenna converts radio frequency electrical
energy fed to it (via the transmission line) to an
electromagnetic wave propagated into space.


Antenna
An antenna is a circuit element that provides a transition from a
guided wave on a transmission line to a free space wave and it
provides for the collection of electromagnetic energy.

Antenna Definition-contd
In transmit systems the RF signal is generated,
amplified, modulated and applied to the
antenna
In receive systems the antenna collects
electromagnetic waves that are cutting
through the antenna and induce alternating
currents that are used by the receiver
Antenna Types
High Frequency
1.6 - 30 Mhz + 50 Mhz
160 - 6 meters

An antennas size/length depends on the
frequency
Its functionality largely depends on the
height above ground, as well as the polarity
and its configuration
Antennas
A good antenna works
A bad antenna is a waste of time & money
Antenna systems can be very inexpensive and simple
They can also be very, very expensive

Antenna Considerations
The space available for an antenna
The proximity to neighbors
The operating frequencies you will use
The output power
Money

Isotropic Antenna
The isotropic antenna is a hypothetical point source.
It does not exist in reality but is considered as an
important starting point considering different antennas
from the theoretical to the practical
The pattern is a Cardioid - a donut shape or a sphere






Current and voltage distribution on an antenna.

1. A current flows in the
antenna with an amplitude
that varies with the generator
voltage.

1. A sinusoidal distribution of
charge exists on the
antenna. Every 1/2 cycle, the
charges reverse polarity.

2. The sinusoidal variation in
charge magnitude lags the
sinusoidal variation in current
by 1/4 cycle.
Standing waves
of voltage and
current on an
antenna.

Reciprocity
An antenna ability to transfer energy form the
atmosphere to its receiver with the same
efficiency with which it transfers energy from the
transmitter into the atmosphere.

Antenna characteristics are essentially the
same regardless of whether an antenna is
sending or receiving electromagnetic energy

Reciprocity

RECIPROCITY of
antennas means that
the various properties
of the antenna apply
equally to transmitting
and receiving
Polarization
Polarization is the direction of the electric field
and is the same as the physical attitude of the
antenna

A vertical antenna will transmit a vertically
polarized wave

The receive and transmit antennas need to
possess the same polarization

Antenna Polarization
- Vertical or horizontal

Vertical waves travel @ 90 to the earths surface
Horizontal waves travel parallel to the earths surface
Usually wire antennas are horizontal but an inverted
V dipole has a vertical component
Yagi type antennas can be either vertical or
horizontal
Circular antennas can be both vertical and horizontal
Usually, horizontally polarized antennas receives less
noise

Terms And Definitions
RADIATION RESISTANCE is the amount of
resistance which, if inserted in place of the
antenna, would consume the same amount of
power that is actually radiated by the antenna.

RADIATION PATTERNS can be plotted on a
rectangular- or polar-coordinate graph. These
patterns are a measurement of the energy
leaving an antenna.

Dipole antenna
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Dipole Antenna
Characteristics
Polarization: vertical
Beamwidth: 80 x 360
Bandwidth: 10%
Gain: 2 dB
Typical Applications
TV Rabbit ears
FM radio (folded dipole)
Radio mast transmitters
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Simplified Radiation Patterns
Elevation,
El
Azimuth,
Az
3-D pattern

Antenna radiation pattern is 3-
dimensional

The 3-D plot of antenna pattern
assumes both angles and varying,
which is difficult to produce and to
interpret 3-D pattern

Source: NK Nikolova
Reference antenna (/2 dipole)
Isotropic antenna or isotropic radiator is a hypothetical (not
physically realizable) concept, used as a useful reference to describe
real antennas.

Isotropic antenna radiates equally in all directions. Its radiation
pattern is represented by a sphere whose center coincides with the
location of the isotropic radiator.

Source: NK Nikolova
Generally speaking, there are two types of antenna:
1. Directional
- this type of antenna has a narrow beamwidth; with
the power being more directional, greater distances
are usually achieved but area coverage is sacrificed
- Yagi, Panel, Sector and Parabolic antennae

2. Omni-Directional
- this type of antenna has a wide beamwidth and
radiates 360
0
; with the power being more spread out,
shorter distances are achieved but greater coverage
attained
- Omni antenna

Omni
- typical gains of 3 to 10 dBi
Radiation Pattern
Radiation pattern is an indication of radiated field
strength around the antenna.

Power radiated from a /2 dipole occurs at right
angles to the antenna with no power emitting
from the ends of the antenna.

Optimum signal strength occurs at right angles or
180 from opposite the antenna
Radiation Patterns
Radiation pattern
Graphical representation of radiation properties of
an antenna
Depicted as two-dimensional cross section
Beamwidth (or half-power beam width)
Measure of directivity of antenna
Reception pattern
Receiving antennas equivalent to radiation pattern
Radiation Pattern for Vertical Antennas
antenna
/4
/2
Antenna Radiation Patterns
Common parameters
main lobe (boresight)
half-power beamwidth (HPBW)
front-back ratio (F/B)
pattern nulls
Typically measured in two planes:
Vector electric field referred to E-field
Vector magnetic field referred to H-field
Typical Radiation Pattern for an Omni
A LOBE is the area
of a radiation pattern
that is covered by
radiation.

A NULL is the area of
a radiation pattern
that has minimum
radiation.

Beamwidth
Beamwidth is the angular separation
of the half-power points of the
radiated pattern
beamwidth
antenna

A
Power 3dB down
from maximum
point A
Max power
2 dipole
Directional Antenna
Radiated energy is
focused in a specific
direction
TYPES OF ANTENNAS
Isotropic antenna (idealized)
Radiates power equally in all
directions
Dipole antennas
Half-wave dipole antenna (or
Hertz antenna)
Quarter-wave vertical antenna
(or Marconi antenna)
Parabolic Reflective Antenna
Antenna
HERTZ (half-wave) and MARCONI (quarter-
wave) are the two basic classifications of
antennas.

HERTS ANTENNA OR HALFWAVE
DIPOLE -consists of two lengths of
rod or tubing, each a quarter-wave
long at a certain frequency, which
radiates a doughnut pattern.

physical length - one-half wavelength
of the applied frequency
called a Hertz antenna or a half-wave
dipole antenna.
Hertz antennas are not found at
frequencies below 2MHz because of
the physical size needed of the
antenna to represent a half-wave.
A QUARTER-WAVE
ANTENNA (Marconi) is a
antennna (total of half-wave
antenna) cut in half with one
end grounded.
Also called Vertical Antennas
are used for frequencies under
2 MHz.
It uses a conducting path to
ground that acts as
wavelength portion the antenna
above the ground.
The above ground structure
represents a /4 wavelength


Types of Antennas
Simple wire
Dipole
Folded dipole
Trap dipole
Offset or Windom antenna
Phased dipoles
Vertical or horizontal (both)
Beverage wave antenna

Types of Antennas
Metal
Vertical
Yagi
Trap Yagi
Phased arrays
Loops
Vertical or Horizontal
Horns for super ultra high frequencies
Mobile antennas

Horizontal and Dipole Antennas
38
A horizontal antenna is an antenna that is a simple dipole
mounted so the elements are parallel to the earth's surface.
So whats a dipole?
A dipole antenna consists of two sections that are
each approximately one-quarter of the wavelength
of that band, so that the total length is equal to
about one-half wavelength. It is a simple antenna
designed to work best on a single band.

The transmission line from the radio is connected
to this antenna in the middle of the two sections.
Dipole Antenna
39
This is an example of a dipole antenna. Many hams getting on HF for
the first time often start with a dipole. If you have the room for one, the
dipole is cheap and easy to build.
Dipole Antenna
Vertical Antennas
A Vertical Antenna- is an antenna that consists of a
single element mounted perpendicular to the earth's
surface.

Most mobile antennas are verticals.
Verticals usually require some sort of counterpoise to
work their best. In a fixed station, a vertical may either be
mounted on the ground or on a mast, and it may also
have several radials for counterpoise.
These radials may be laid out on the ground, as in the
next slide, or mounted just underneath the vertical
element, as in an elevated ground plane.
In a mobile installation, the metal body of the car usually
serves as the counterpoise.
Vertical (Marconi) Antenna contd
Poor grounding conditions of the earth/soil
surrounding the antenna can result in serious
signal attenuation.

This problem is alleviated by installing a
counterpoise
Counterpoise
Counterpoise is a grounding grid established
where the earth grounding cannot satisfy
electrical requirements for circuit completion.

It is designed to be non-resonant at the
operating frequency
Counterpoise-contd
supports
antenna
radius =
Typical Ground-Mounted Vertical
45
This is a rough diagram of a ground-mounted vertical. The
orange radials you see may be laid along the top of the ground or
buried just beneath the surface.

The GROUND SCREEN and the COUNTERPOISE are used to reduce
losses caused by the ground in the immediate vicinity of the antenna.
The ground screen is buried below the surface of the earth. The
counterpoise is installed above the ground.
Ground Plane Antenna
47
Ground plane antenna another type of vertical
antenna. It is designed to be mounted on a mast,
and usually has three or four radials coming from
the base of the antenna.
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Whip Antenna
El
Az
Characteristics
Polarization: vertical
Beamwidth: 45 x 360
Bandwidth: 10%
Gain: 0 dB
Typical Applications
Automobile radio and satellite
signals
Military (army)
communications
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Loop
El
Az
Characteristics
Polarization: horizontal
Beamwidth: 80 x 360
Bandwidth: 10%
Gain: -2 dB
Typical Applications
AM Broadcasting
The FOLDED DIPOLE consists of a dipole
radiator, which is connected in parallel at its ends
to a half-wave radiator.

A LONG-WIRE ANTENNA is an antenna that is a
wavelength or more long at the operating
frequency.

These antennas have directive patterns that are
sharp in both the horizontal and vertical planes.

BEVERAGE ANTENNAS consist of a single wire
that is two or more wavelengths long.

A V ANTENNA is a bidirectional antenna consisting
of two horizontal, long wires arranged to form a V.

The RHOMBIC ANTENNA uses four conductors joined to
form a rhombus shape. This antenna has a wide frequency
range, is easy to construct and maintain, and is noncritical as
far as operation and adjustment are concerned.
Helical
El & Az
Characteristics
Polarization: circular (axial
mode)
Beamwidth: 50 x 50
Bandwidth: 70%
Gain: 10 dB
Typical Applications
Mobile communications
GPS
Space communication
Animal tracking
The TURNSTILE ANTENNA consists of two
horizontal, half-wire antennas mounted at right
angles to each other.
ANTENNA LOADING is the method used to change the
electrical length of an antenna.

This keeps the antenna in resonance with the applied
frequency. It is accomplished by inserting a variable
inductor or capacitor in series with the antenna.

Antenna Array
Antenna array is a group of antennas or
antenna elements arranged to provide the
desired directional characteristics.

Generally any combination of elements can
form an array. However, equal elements in a
regular geometry are usually used.


AN ARRAY is a combination of half-wave elements operating together
as a single antenna. It provides more gain and greater directivity than
single element antennas.

A DRIVEN ARRAY derives its power directly from the source.
A PARASITIC ARRAY derives its power by coupling the energy from
other elements of the antenna.

The BIDIRECTIONAL ARRAY radiates energy equally in two opposing
directions.
The UNIDIRECTIONAL ARRAY radiates energy efficiently in a single
direction.

The COLLINEAR ARRAY has elements in a straight line. Maximum
radiation occurs at right angles to this line.
The BROADSIDE ARRAY has elements parallel and in the same
plane. Maximum radiation develops in the plane at right angles to the
plane of the elements.



The BROADSIDE ARRAY has elements parallel and in the same
plane. Maximum radiation develops in the plane at right angles to
the plane of the elements.



The END-FIRE ARRAY has elements parallel to each other and in the
same plane. Maximum radiation occurs along the axis of the array.

Phased Array
El
Az
Characteristics
Polarization: linear / circular
Beamwidth: 0.5 x 30
Bandwidth: varies
Gain: 10 to 40 dB
Typical Applications
Radio broadcasting
Search & track radar
Weather radar
(severe storm watch)
Military Phased Array Usage
Phased array antennas
Phased array antennas have become an
extremely important type of radar for military
use, particularly airborne use.
In radar applications, phased arrays permit
near instant switching from one target to
another, and from search to track mode.
Phased arrays combined with smart skin
technology have radically altered airborne
avionics designs.
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Basic phased array architecture
Signal Divider
/ Combiner
Phase
Shifter
Phase
Shifter
Phase
Shifter
Phase
Shifter
Phase
Shifter
Phase
Shifter
Steering angle,
s

Element spacing
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Phased array gain
The gain of a phase array antenna is a
function of the number of elements in the
array and the gain of the individual elements

For half-wavelength element spacing, the gain at
boresight is given by:
G = 10 log (N) + G
e

The gain off-boresight is reduced by the cosine of
the steering angle,
s
:
G = 10 log (N) + G
e
+ 10 log (cos
s
)


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Phased array beamwidth
The beamwidth of a phased array antenna is
a function of the number of elements.
For a half-wavelength phased array of dipole
elements the half-power beamwidth is given by:

3-dB u
B
= 102/N where N = no. of arrays

The beamwidth at off-boresight steering angles
increases with the cosine of
s
:

3-dB u
B
= (102/N) / cos(
s
)
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Beam steering limitations
A phased array antenna with half-wavelength
spacing is limited to beam steering angles of
45 off boresight.

Greater steering angles can be achieved by
reducing the element separation at the
expense of boresight gain.
Pointers in antenna design:

MATCHING STUBS are used between elements to maintain
current in the proper phase.

The GAIN OF A COLLINEAR ANTENNA is greatest when the
elements are spaced from 0.4 to 0.5 wavelength apart or when
the number of elements is increased.

The OPTIMUM GAIN OF A BROADSIDE ARRAY is obtained
when the elements are spaced 0.65 wavelength apart.

A PARASITIC ARRAY consists of one or more parasitic
elements with a driven element. The amount of power gain and
directivity depends on the lengths of the parasitic elements and
the spacing between them.

ARRAYS, such as the YAGI, have a narrow Frequency
response as well as a narrow beamwidth.
Yagi-Uda Antenna
The Yagi-Uda antenna is a simple form of a
directional antenna based on a reflector
placed /4 from the dipole antenna
placement.

Yagi-Uda Antenna-contd
reflector
dipole
antenna
/4
antenna
2 dipole radiated signal
without reflector
2 dipole radiated signal
with reflector
Radiated Directed Signal
The Antenna Formula
= c ]
f = frequency of the signal
c = is the speed of light = 186,000 mi/sec
= is the wavelength of the signal, use 3 x 10
8

when dealing in meters for the speed of light

The Antenna Formula - applied
If a half-wave dipole antenna needed to be
constructed for a 60 Hz signal, how large
would it need to be?
= c] = 186,000 misec
60
= 3100 mi
2 = 1550 miles!
Radiation & Induction Fields
The mechanics launching radio frequencies
from an antenna are not fully understood.
The RF fields that are created around the
antenna have specific properties that affect
the signals transmission.
The radiated field is known as the radiation
field
Radiation & Induction Fields-contd
There are two induction fields or areas where
signals collapse and radiate from the antenna.
They are known as the near field and far
field.
The distance that antenna inductance has on
the transmitted signal is directly proportional
to antenna height and the dimensions of the
wave.
R >
2D
2


Radiation & Induction Fields-contd
R > 2D
2


Where: R = the distance from the antenna
D = dimension of the antenna
= wavelength of the transmitted
signal
Radiation Resistance
Radiation Resistance is the portion of the antennas
impedance that results in power radiated into space
(i.e., the effective resistance that is related to the power
radiated by the antenna.

Radiation resistance varies with antenna length.
Resistance increases as the increases
Antenna Impedance
A proper Impedance Match is essential for maximum
power transfer. The antenna must also function as a
matching load for the Transmitter ( 50 ohms).

Voltage Standing Wave Ratio (VSWR), is an indicator
of how well an antenna matches the transmission line
that feeds it. It is the ratio of the forward voltage to the
reflected voltage.

The better the match, the lower the VSWR. A value of
1.5:1 over the frequency band of interest is a practical
maximum limit.
Return Loss is related to VSWR, and is a measure of
the signal power reflected by the antenna relative to
the forward power delivered to the antenna.
The higher the value (usually expressed in dB), the
better.
A figure of 13.9dB is equivalent to a VSWR of 1.5:1.
A Return Loss of 20dB is considered quite good, and is
equivalent to a VSWR of 1.2:1.
VSWR Return Loss Transmission Loss
1.0:1

0.0 dB
1.2:1 20.83 dB 0.036 dB
1.5:1 13.98 dB 0.177 dB
5.5:1 3.19 dB 2.834 dB
Point-Source Radiator
Consider a source of electro-magnetic radiation that
radiates in all directions equally.
Such a source is called isotropic.
Let the total power radiated by the source be P
T
.
Let the source be surrounded by a sphere or radius d.
If there are no objects inside the sphere to absorb or
reflect the radiation, all of the power from the source
will hit or cross the sphere.
The surface area of a sphere is 4d
2
.
Power Concentrator
If a reflector were added to the point source, more of
the power would go in one direction that the others.

This increase in power (over isotropic) can be
expressed as the power gain GT of the antenna.

Since the antenna is a passive device, it cannot
actually increase the total power radiated.

The higher the gain of the antenna, the more focused
is the power in one direction.

The gain only applies along the bore sight of the
antenna.
Antenna Gain
The antenna power gain is defined as









Since an antenna is a passive device, it has the
same gain whether it is transmitting or receiving.
Effective Isotropic Radiated Power
The Effective Isotropic Radiated Power (EIRP) of
an antenna is power input required of an isotropic
antenna to produce the same power density on the
bore sight as the actual antenna.
P
ERIP
= P
T
G
T
Power Density at d = (P
ERIP
)/ (4d
2
)
= (P
T
G
T
)/(4d
2
) (w/m
2
)

d = distance from the antenna
The EIRP is the transmitted power multiplied by the
gain of the transmitting antenna.
Effective Radiated Power (ERP)
ERP = the power input value multiplied by the
gain of the antenna

dBi = isotropic radiator gain
dBd = dipole antenna gain
Effective Area
If the receiving antenna is placed d meters from
the transmitting antenna, it will act like a catchers
mitt and intercept the power in an effective area
of Ae (m2).
watt
Effective area - Related to physical size and shape of
antenna
Antenna Gain
Antenna gain is the measure in dB
how much more power an antenna
will radiate in a certain direction with
respect to that which would be
radiated by a reference antenna
Antenna Gain

Directive Gain ratio of the power density in a particular
direction of one antenna to the power density that would
be radiated by an omnidirectional antenna (isotropic
antenna).

Directivity refers to the ability of an antenna to send
and/or receive signals over a narrow horizontal directional
range.

Gain of Hertzian Dipole with respect to an isotropic
antenna = 1.5:1 or 10 log 1.5 = 1.76 dB gain over
isotropic source.

The gain of a half-wave dipole compared to the isotropic
antenna = 1.64:1 or 10 log 1.64 = 2.15 dB.

Antenna Gain
Relationship between antenna gain and effective
area




G = antenna gain
A
e
= effective area
f = carrier frequency
c = speed of light (3 X 10
8
m/s)
= carrier wavelength
2
2
2
4 4
c
A f A
G
e e
t

t
= =
Antennas Gain
Gain
( ) ( )
, , G eD u | u | =
The power gain, G, of an antenna is very much like its
directive gain, but also takes into account efficiency
The maximum power gain
max max
G eD =
The maximum power gain is often expressed in dB.
( ) ( )
max max
10
10log G G dB =
Antenna Height
Antenna height above the ground is directly related to
radiation resistance. Ground reflections causing out-
of-phase signals to be radiated to receiving antennas
will degrade the transmission.

Physical length and electrical length of most antennas
are approximately 95% of the physical length. Ideal
antenna height is usually based on trial and error
procedures
Dipole Length:

Antenna is a frequency sensitive device.
= c/f
= 984/f
(MHz)
;

/2 = 492/f
(MHz)
(feet)

Example:

f = 122 MHz

/2 = 492/f
(MHz)
= 492/122 = 4.033 feet.

End Effect:

/2 = 492/f
(MHz)
x 0.95 = 468/f(MHz)

If f= 27 MHz. L = 468/27 = 17.333 feet,
therefore

/4 = 8.66 feet.

Antenna Q and Bandwidth:

Bandwidth is determined by the frequency of operation while Q is the
quality of the antenna circuit.

BW = f/Q

If Q is high bandwidth is narrow, if Q is low, BW is wider.
For resonant circuit Q>10, which makes the circuit more selective.
SWR below 2:1 good design

Q and BW- are determined primarily by the ratio of the length to the
diameter of the conductor. Also affected by the number of conductors
used and their spacing to the dipole.

Q= X
L
/ R
BW = F/Q
Note: Lowering Q increases the BW; lower Xl reduces Q and increases BW. UHF
antenna- short and fat conductors are used to improve Q and BW.


= c/f c= velocity of EMW

L = c/f x 0.95 Vf= 0.95 c (end effect)

L = (3x 10
8
/ 5 X 10
5
)X 0.95 = 570 meters

or 2244 feet
Problem:

Determine the length of an antenna operating at
frequency 500 KHz.

Antenna Characteristics:

1. The longer the antenna length, the higher the directive gain.
HW dipole Gain = 1.64 (2.15dB); 8 dipole Gain = 7.1
(8.51dB)
2. Non-resonant antenna have higher directive gain than
resonant antenna.

Non-resonant Antenna (Directional Antenna) similar to a
properly terminated transmission line, produces no standing
waves. Reflected waves are suppressed by the terminating
resistance (resistor) at the point farthest from the feed point.

Resonant Antenna standing waves exist; a multiple of half-
wavelenghts of the signal frequency.


Directivity and Power Gain

Power Gain comparison of the output power of an
antenna in a certain direction to that of an isotropic
antenna.

Antenna Gain is the power ratio comparison between
an omnidirectional and unidirectional radiator.

A(dB) = 10 log (P
2
/P
1
)

Where: P
1
= power of unidirectional antenna


P
2
= power of the reference antenna


A
(dB)
= 10 log (P
2
/P
1
)

2.15 dB = 10 log (P
2
/1000)

P
2
/1000 = log -1 (2.15/10)

P
2
= 1.64 x 1000 = 1640 watts

Problem:

A half-wave dipole antenna is capable of radiating 1-kW
and has a 2.15 dB gain over an isotropic antenna. How
much power will be delivered to the isotropic
(omnidirectional) antenna, to match the filed strength of
a directional antenna?

ERP (Effective Radiated Power) - field gain of the
antenna and the efficiency of the transmitter.

ERP = P
o
x (Field Gain)
2

Example:

If an antenna has a field gain of 2 and the transmitter
has an overall efficiency of 50% (circuit and xmission
line losses) then, if a 1-kW signal is fed to the finals,
this will results in 500 w being fed to the antenna.
What is the ERP?

ERP = P
o
x (Field Gain)
2
= 500 x 2
2
= 2000 w



Radiation and Field Intensity

Field Intensity the field of an antennas radiation at a
given point in space, is equal to the amount of voltage
induced in a wire antenna 1 meter long, located a that
given point.

Factors affecting FI: time, atmospheric condition and
distance.

Antenna Resistance hypothetical value which, if replaced
by an equivalent resistor, would dissipate exactly the same
amount of power that the antenna would radiate. This is
the ration of the power radiated by the antenna to the
square of the current at the feed point.
Antenna Losses and Efficiency

Antenna Losses due to the ground resistance, corona effects,
imperfect dielectric near the antenna, energy loss due to eddy current
induced into nearby metallic objects, and I
2
R losses in the antenna
itself.

P
in
= P
d
+ P
rad
P
in
power delivered to the feed point
P
d
power lost
P
rad
power actually radiated

I
2
R
in
= I
2
R
d
+ I
2
R
rad
R
in
= R
d
+ R
rad


Antenna Efficiency = = (R
rad
/ (R
d
+ R
rad
)



Low and medium frequency antenna approximately 75 to 95 %
efficiency. HF antenna have approximately 100% efficency.
Antennas Efficiency
Power is fed to an antenna through a T-Line and
the antenna appears as a complex impedance
Efficiency
.
ant ant ant
Z R jX = +
ant rad dis
R R R = +
where the antenna resistance consists of
radiation resistance and and a dissipative
resistance.
2
1
2
rad o rad
P I R =
2
1
2
diss o diss
P I R =
The power dissipated by ohmic losses is The power radiated by the antenna is
An Antenna Efficiency e can be defined as the ratio of the radiated
power to the total power fed to the antenna.
rad rad
rad diss rad diss
P R
e
P P R R
= =
+ +
For the antenna is driven by phasor current
j
o s
I I e
o
=
Example
Suppose an antenna has directivity (gain) D = 4, R
rad
= 40 O
and R
diss
= 10 O. Find antenna efficiency and maximum power
gain.

40
10 40
0.8 (or) 80%
rad
rad diss
R
e
R R
=
+ +
= =
Antenna efficiency is
Maximum power gain is
( )( )
max max
4 0.8 3.2 G eD = = =
( ) ( ) ( )
max max
10 10
10log 10log 3.2 5.05 G G dB = = =
Maximum power gain in dB is
An antennas polarization is relative to the E-
field of antenna.
If the E-field is horizontal, than the antenna is
Horizontally Polarized.
If the E-field is vertical, than the antenna is
Vertically Polarized.
Polarization
No matter what polarity you choose, all antennas in
the same RF network must be polarized identically
regardless of the antenna type.
Polarization may deliberately be used to:
Increase isolation from unwanted signal sources (Cross
Polarization Discrimination (x-pol) typically 25 dB)
Reduce interference
Help define a specific coverage area

Horizontal

Vertical
More on Dipoles
110
Dipoles may be mounted either horizontally or
vertically, depending on the intended use.
May be made from wire or metal tubing, and are
very easy for a new ham to construct.
Wire dipoles are also fairly inexpensive and
simple to design.

With an antenna tuner, they can also be made
to work on several bands. For these reasons,
they are very popular with new hams (amateur
radio) on the HF bands.
Beam Antennas
112
A beam antenna is an antenna that concentrates signals in one direction.

It is designed to focus all of the energy produced by your transmitter in the
direction you want to work. Focusing your signal power in one direction
makes for a stronger signal in that direction. Beams are effective, but
depending on the bands covered and type, they can be expensive.
Beam Antennas - Quad
113
The quad, Yagi, and dish are all examples of beam
antennas. A quad antenna looks something like a metal
frame for a box kite. If you look closely, you can see the
antenna wires supported by the X framework.
Quad antenna
Beam Antennas - Yagi
115
The yagi is a one dimensional beam antenna
consisting of several elements. It may be mounted
horizontally, as shown here, or vertically.
EEE381B
Log Periodic
El
Az
Characteristics
Polarization: vertical / horizontal
Beamwidth: 80 x 60
Bandwidth: 10 to 1
Gain: 6 to 8 dB
Typical Applications
Amateur radio
EEE381B
Yagi
El
Az
Characteristics
Polarization: horizontal
Beamwidth: 90 x 50
Bandwidth: 5%
Gain: 5 to 15 dB
Typical Applications
WWII airborne radar
Amateur radio
Yagi
- better suited for shorter links
- lower dBi gain; usually between 7 and 15 dBi
Typical Radiation Pattern for a Yagi
LOG PERIODIC ANTENNA
EEE381B
Cavity Backed Spiral
El & Az
Characteristics
Polarization: circular
Beamwidth: 80 x 80
Bandwidth: 9 to 1
Gain: -15 to +3 dB
Typical Applications
Radar altimeter
Electronic warfare
EEE381B
Conical Spiral
El & Az
Characteristics
Polarization: circular
Beamwidth: 60 x 60
Bandwidth: 4 to 1
Gain: 5 to 8 dB
Typical Applications
Ground penetrating radar
Electronic warfare
EEE381B
Horn
El
Az
Characteristics
Polarization: linear / circular
Beamwidth: 40 x 30
Bandwidth: 4 to 1
Gain: 4 to 10 dB
Typical Applications
Radio astronomy
Electronic warfare
Antenna testing
EEE381B
Largest Horn Antenna
It was from this historic radio astronomy horn
antenna that microwave background radiation
was discovered, helping to confirm the Big
Bang theory
Beam Antennas - Dish
127
Another beam antenna is the dish or parabolic
reflector. It is often used to receive UHF signals or
TV signals beamed from satellites, such as Dish
Network antennas.
EEE381B
Parabolic
El & Az
Characteristics
Polarization: depends on feed
Beamwidth: 0.5 x 30
Bandwidth: varies
Gain: 10 to 55 dB
Typical Applications
Satellite TV
Cellular telephony, Wi-Fi
Radio astronomy
Search & track radar
PARABOLIC ANTENNA
The parabolic dish antenna -
consists of one circular
parabolic reflector and a point
source situated in the focal
point of this reflector. This
point source is called primary
feed or feed.

The circular parabolic
(paraboloid) reflector is
constructed of metal, usually a
frame covered by metal mesh
at the inner side. The width of
the slots of the metal mesh
has to be less than /10. This
metal covering forms the
reflector acting as a mirror for
the radar energy.
Parabolic
- used in medium to long links
- gains of 18 to 28 dBi
- most common
Typical Radiation Pattern for a Parabolic
PARABOLIC ANTENNA
RADIATION PATTERN
THE CASEGRAIN ANTENNA

In telecommunication and radar use, a Cassegrain antenna is an antenna in
which the feed radiator is mounted at or near the surface of a concave main
reflector and is aimed at a convex subreflector. Both reflectors have a common
focal point. Energy from the feed unit (a feed horn mostly) illuminates the
secondary reflector, which reflects it back to the main reflector, which then forms
the desired forward beam.


QUESTIONS

Isotropic Source

1. What is an isotropic antenna? hypothetical
point source
2. Describe the antenna radiation pattern for an
isotropic radiator? A sphere
3. What determines the polarization of an
antenna? the electric field
4. What does horizontal wave polarization
mean? The electric lines of force of the
radio wave is parallel to the earth's surface
5. What does vertical wave polarization mean?
The electric lines of force of a radio wave
are perpendicular to the earth's surface


1. What electromagnetic wave polarization does a Yagi
antenna have when its elements are parallel to the
earth's surface? Horizontal
2. What electromagnetic wave polarization does a half-
wavelength antenna have when it is perpendicular to
the earth's surface? Vertical
3. VHF signals from a mobile station using a vertical whip
antenna will normally be best received using a:
vertical ground-plane antenna
4. A dipole antenna will emit a vertically polarized wave if
it is: Parallel with the ground mounted vertically
5. If an electromagnetic wave leaves an antenna vertically
polarized, it will arrive at the receiving antenna, by
ground wave: vertically polarized
6. Compared with a horizontal antenna, a vertical antenna
will receive a vertically polarized radio wave:
at greater strength

2
|
.
|

\
|
=

t
q
D
G
141
Microwave Parameters:
General Equation:
B. Parabolic Antenna Gain, G
where:
D = antenna diameter in m
= signal wavelength in m
= efficiency
2
6
|
.
|

\
|
=

D
G
142
Microwave Parameters:
Antenna Gain for Typical Values of (0.55 to 0.75):
Parabolic Antenna Gain for Typical Values of (0.55 to
0.75) in Metric system:
) ( 10 ) ( 10
log 20 log 20 4 . 42
m MHz
D f G + + =
) ( 10 ) ( 10
log 20 log 20 8 . 17
m GHz
D f G + + =
143
Microwave Parameters:
Parabolic Antenna Gain for Typical Values of
(0.55 to 0.75) in English system:
) ( 10 ) ( 10
log 20 log 20 6 . 52
ft MHz
D f G + + =
) ( 10 ) ( 10
log 20 log 20 5 . 7
ft GHz
D f G + + =
Sectoral
- directional in
nature, but can be
adjusted anywhere
from 45
0
to 180
0
- typical gains vary
from 10 to 19 dBi

GSM and
CDMA cellsite
antenna
array for the
cellular
telephone
system``
0
90
180
270 0 -3 -6 -10
-15
-20
-30
dB
0
90
180
270 0 -3 -6 -10
-15
-20
-30
dB
Typical Radiation Pattern for a Sector
Beamforming Antenna
Beamforming Antenna Array
Smart Antennas
SMART ANTENNA
A smart antenna is a digital wireless communications
antenna system that takes advantage of diversity effect at
the source (transmitter), the destination (receiver), or
both.

Diversity effect involves the transmission and/or reception
of multiple radio frequency (RF) waves to increase data
speed and reduce the error rate.
SMART ANTENNA
Smart antennas fall into three major categories:
1.SIMO (single input, multiple output),
2.MISO (multiple input, single output), and
3.MIMO (multiple input, multiple output).

In SIMO technology, one antenna is used at the source,
and two or more antennas are used at the destination.
In MISO technology, two or more antennas are used at
the source, and one antenna is used at the destination.
In MIMO technology, multiple antennas are employed at
both the source and the destination.
MIMO has attracted the most attention recently because
it can not only eliminate the adverse effects of multipath
propagation, but in some cases can turn it into an
advantage.
Smart Antennas
Smart antennas (also known as adaptive
array antennas, multiple antennas and,
recently, MIMO)

are antenna arrays with smart signal
processing algorithms used to identify spatial
signal signature such as the direction of
arrival (DOA) of the signal, and use it to
calculate beamforming vectors, to track and
locate the antenna beam on the mobile/target.
The antenna could optionally be any sensor.
Smart Antennas
Smart Antennas are base station antennas with a
pattern that is not fixed, but adapts to the current
radio conditions
Smart Antennas have the possibility for a large
increase in capacity: an increase of three times
for TDMA systems and five times for CDMA
systems has been reported.
Major drawbacks and cost factors include
increased transceiver complexity and more
complex radio resource management
Smart Antennas
The idea of smart antennas is to use base
station antenna patterns that are not fixed, but
adapt to the current radio conditions.
This can be visualized as the antenna directing
a beam toward the communication partner only
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 and UMTS.

Smart Antennas
Smart antennas add a new way of separating
users, namely by space, through SDMA
(space division multiple access)

By maximizing the antenna gain in the desired
direction and simultaneously placing minimal
radiation pattern in the directions of the
interferers, the quality of the communication
link can be significantly improved
Smart Antenna
Elements of a Smart Antenna
Smart antennas consists of a number of radiating
elements, a combining/dividing network and a
control unit
Phased Array Antenna
Phased Array antennas are a
combination of antennas in which
there is a control of the phase and
power of the signal applied at each
antenna resulting in a wide variety
of possible radiation patterns
Types of Intelligent Antennas
Switched lobe (SL):
This is also called switched beam.
It is the simplest technique, and comprises only
a basic switching function between separate
directive antennas or predefined beams of an
array.
The setting that gives the best performance,
usually in terms of received power, is chosen
Intelligent Antennas-
Dynamically phased array (PA):

By including a direction of arrival (DoA) algorithm
for the signal received from the user, continuous
tracking can be achieved and it can be viewed as
a generalization of the switched lobe concept
Intelligent Antennas-
Adaptive array (AA): In this case, a DoA algorithm for
determining the direction toward interference sources
(e.g., other users) is added.
The radiation pattern can then be adjusted to null out
the interferers.
In addition, by using special algorithms and space
diversity techniques, the radiation pattern can be
adapted to receive multipath signals which can be
combined.
These techniques will maximize the Signal To
Interference Ratio (SIR)
SMDA
SPACE DIVISION MULTIPLE ACCESS

(SDMA) implies that more than one user can be
allocated to the same physical communications
channel simultaneously in the same cell, only
separated by angle.

In a TDMA system, two users will be allocated to
the same time slot and carrier frequency at the
same time and in the same cell
SMDA-
In systems providing full SDMA, there will be
much more intracell handovers than in
conventional TDMA or CDMA systems, and more
monitoring by the network is necessary
Antenna Installation Considerations
Safety
standard operating procedure priority
Grounding
lightning strikes
static charges
Surge protection
lightning searches for a second path to ground
Antenna Installation
Considerations-
Adaptive array antenna placement needs to be
considered differently than current technologies
serving the mobile environment.

They need to be placed so as to have a greater
angular approach to the receiving units.

Existing tower placement with close proximity to
roads and highways would need to be
reconsidered.
Antenna Installation Considerations
Base, mast, and supporting
structure needs clearance,
serviceability (access), and
complies with the municipal
guidelines (electrical and building
code)
EEE381B
Antenna selection
Selection of an appropriate antenna for a system
is highly application dependent
Factors include:
Angular coverage
Frequency of operation & bandwidth
Polarization
Power gain
EEE381B
Antenna types
]

Angular
Coverage
Polarization Bandwidth Type

360
azimuth
Linear Narrow
Wide
Whip, dipole, loop
Biconical, swastika
Circular Narrow
Wide
Helix
Conical spiral

Directional
Linear Narrow
Wide
Yagi, dipole array
Log periodic, horn, dish*
Circular Narrow
Wide
Horn with polarizer
Cavity-backed spiral, dish*
* Dish characteristics depend on the feed
QUESTIONS?????
1. What are the two basic classifications of antennas?
2. What are the three parts of a complete antenna system?
3. What three factors determine the type, size, and shape of
an antenna?
4. If a wave travels exactly the length of an antenna from
one end to the other and back during the period of 1
cycle, what is the length of the antenna?
5. What is the term used to identify the points of high
current and high voltage on an antenna?
6. What is the term used to identify the points of minimum
current and minimum voltage on an antenna?
7. The various properties of a transmitting antenna can
apply equally to the same antenna when it is used as a
receiving antenna. What term is used for this property?
8. The direction of what field is used to designate the
polarization of a wave?
9. If a wave's electric lines of force rotate through 360
degrees with every cycle of rf energy, what is the
polarization of this wave?


ANSWERS:
1. Half-wave (Hertz) and quarter-wave
(Marconi).
2. Coupling device, feeder, and antenna.
3. Frequency of operation of the transmitter,
amount of power to be radiated, and
general direction of the receiving set.
4. One-half the wavelength.
5. Current and voltage loops.
6. Current and voltage nodes.
7. Reciprocity of antennas.
8. Electric (E) field.
9. Circular polarization.





10. What type of polarization should be used at medium and low
frequencies?
11. What is an advantage of using horizontal polarization at high
frequencies?
12. What type of polarization should be used if an antenna is mounted
on a moving vehicle at frequencies below 50 megahertz?
13. What is the radiation resistance of a half-wave antenna in
free space?
14. A radiating source that radiates energy stronger in one
direction than another is known as what type of radiator?
15. A radiating source that radiates energy equally in all
directions is known as what type of radiator?
16. A flashlight is an example of what type of radiator?
17. What terms are often used to describe basic half-wave
antennas?
18. If a basic half-wave antenna is mounted vertically, what type
of radiation pattern will be produced?
19. In which plane will the half-wave antenna be operating if it is
mounted horizontally?

ANSWERS:

10. Vertical polarization.
11. Less interference is experienced by man-made
noise sources.
12. Vertical polarization.
13. 73 ohms.
14. Anisotropic radiator.
15. Isotropic radiator.
16. Anisotropic radiator.
17. Dipole, doublet and Hertz.
18. Nondirectional.
19. Vertical plane.


20. Since the radiation pattern of a dipole is similar to
that of a doublet, what will happen to the pattern
if the length of the doublet is increased?
21. What is the simplest method of feeding power to
the half-wave antenna?
22. What is the radiation pattern of a quarter-wave
antenna?
23. Describe the physical arrangement of a ground
screen.
24. What is the difference in the amount of impedance
between a three-wire dipole and a simple center-
fed dipole?
25. Which has a wider frequency range, a simple
dipole or a folded dipole?
ANSWERS:

20. The pattern would flatten.
21. To connect one end through a capacitor to the
final output stage of the transmitter.
22. A circular radiation pattern in the horizontal
plane, or same as a half wave.
23. It is composed of a series of conductors
arranged in a radial pattern and buried 1 to 2
feet below the ground.
24. Nine times the feed-point impedance.
25. Folded dipole.





Problems:

1. A TV receiving antenna is to be constructed for channel 13. The spacing
between the reflector and dipole should be 2/10 of the wavelength. The
spacing between director and dipole should be 1/10 of a wavelength. The
length of the director is 5% shorter than the dipole and the reflector is 5%
longer than the dipole. Determine the following: a. Length of the dipole; b.
Length of the reflector; c. Length of the director d. Spacing between the
dipole and the reflector; e. Spacing between the dipole and the director.
Note: the length of the dipole should be 5% shorter than /2 to
compensate for the end effect due to capacitance of the antenna.

2. A half-wave antenna has a center impedance of 70 ohms. It is coupled to
a flat 600 ohms transmission line through a quarter wavelength
transmission line. A. Determine the required impedance of the quarter
wave section.; B. Determine the length of the quarter wavelength section
if it is constructed of an air insulated parallel line. Assume that the velocity
factor is 0.975 and the operating frequency of the antenna is 8 MHz.


Problems:


3. A 25 watt SSB transceiver operates on 10 KHz for a point
to point communication. A balanced open two-wire feeder
line spaced 10 inches apart with a wire diameter of 0.125
inch and a half dipole antenna is used for this system.
Determine a) Length of the antenna; b) system
wavelength; c) Zo of the feeder line; d) differentiate short
and long antenna
4. Calculate the length of the following antennas and state
their radiation resistance at 310 . a) dipole; b. Folded
dipole (twin lead; Z = 300 ohms; Vf= 0.8); c. Bow tie
antenna ( = 35 o; 0.73); d) ground plane vertical.


QUESTIONS ??????
Wavelength vs Physical Length

1. The speed of a radio wave: is the same as the
speed of light
2. The velocity of propagation of radio frequency
energy in free space is: 300 000 kilometers per
second
3. If an antenna is made longer, what happens to its
resonant frequency? It decreases
4. If an antenna is made shorter, what happens to its
resonant frequency? It increases
5. The resonant frequency of an antenna may be
increased by: shortening the radiating element

Wavelength vs Physical Length

1. To lower the resonant frequency of an antenna, the
operator should: lengthen it

2. Adding a series inductance to an antenna would:
decrease the resonant frequency

Wavelength vs Physical Length
1. The wavelength for a frequency of 25 MHz is:
12 metres (39.4 ft)
1. The wavelength corresponding to a frequency of 2
MHz is:
150 m (492 ft)
1. At the end of suspended antenna wire, insulators
are used. These act to: limit the electrical length
of the antenna
2. One solution to multi-band operation with a
shortened radiator is the "trap dipole" or trap
vertical. These "traps" are actually: a coil and
capacitor in parallel

Gain, Directivity

1. What is meant by antenna gain?
The numerical ratio relating the radiated signal strength of an
antenna to that of another antenna
1. The gain of an antenna, especially on VHF and above, is quoted in dBi.
The "i" in this expression stands for: Isotropic
2. Approximately how much gain does a half-wave dipole have over an
isotropic radiator? 2.1 dB
3. What is a parasitic beam antenna?
An antenna where some elements obtain their radio energy by
induction or radiation from a driven element
1. If a slightly shorter parasitic element is placed 0.1 wavelength away from
an HF dipole antenna, what effect will this have on the antenna's radiation
pattern? A major lobe will develop in the horizontal plane, toward the
parasitic element
2. If a slightly longer parasitic element is placed 0.1 wavelength away from
an HF dipole antenna, what effect will this have on the antenna's radiation
pattern? A major lobe will develop in the horizontal plane, away from
the parasitic element, toward the dipole

Gain, Directivity
1. In free space, what is the radiation characteristic of a
half-wave dipole? Minimum radiation from the ends,
maximum broadside
2. The front-to-back ratio of a beam antenna is: the ratio
of the maximum forward power in the major lobe to
the maximum backward power radiation
3. The property of an antenna, which defines the range of
frequencies to which it will respond, is called its:
Bandwidth
4. What is meant by antenna bandwidth? The frequency
range over which the antenna may be expected to
perform well
5. How can the bandwidth of a parasitic beam antenna be
increased? Use larger diameter elements

Vertical Antenna

1. To calculate the length in metres (feet) of a quarter wave
vertical antenna you would : Divide 71.5 (234) by the
antenna's operating frequency (in MHz)

2. If you made a quarter-wavelength vertical antenna for
21.125 MHz, how long would it be? 3.6 metres (11.8 ft)

3. If you made a half-wavelength vertical antenna for 223
MHz, how long would it be? 64 cm (25.2 in)

4. If a magnetic-base whip antenna is placed on the roof of
a car, in what direction does it send out radio energy? It
goes out equally well in all horizontal directions

5. What is an advantage of downward sloping radials on a
ground plane antenna? It brings the feed point
impedance closer to 50 ohms
Vertical Antenna
1. What happens to the feed point impedance of a ground-
plane antenna when its radials are changed from horizontal
to downward-sloping? It increases
2. Which of the following transmission lines will give the best
match to the base of a quarter-wave ground-plane antenna?
50 ohms coaxial cable
3. The main characteristic of a vertical antenna is that it will:
receive signals equally well from all compass points
around it
4. Why is a loading coil often used with an HF mobile vertical
antenna? To tune out capacitive reactance
5. What is the main reason why so many VHF base and mobile
antennas are 5/8 of a wavelength? The angle of radiation
is low
6. Why is a 5/8-wavelength vertical antenna better than a 1/4-
wavelength vertical antenna for VHF or UHF mobile
operations? A 5/8-wavelength antenna has more gain
Yagi Antenna
1. How many directly driven elements do most Yagi antennas
have? One
2. Approximately how long is the driven element of a Yagi
antenna for 14.0 MHz? 10.21 metres (33 feet and 6
inches)
3. Approximately how long is the director element of a Yagi
antenna for 21.1 MHz? 6.4 metres (21 feet)
4. Approximately how long is the reflector element of a Yagi
antenna for 28.1 MHz? 5.33metres (17.5 feet long)
5. The spacing between the elements on a three-element Yagi
antenna, representing the best overall choice, is : 0.2 of a
wavelength.
6. What is one effect of increasing the boom length and adding
directors to a Yagi antenna? Gain increases
7. What are some advantages of a Yagi with wide element
spacing? High gain, less critical tuning and wider
bandwidth

Wire Antenna

1. If you made a half-wavelength dipole antenna for
28.550 MHz, how long would it be? 5.08 metres
(16.62 ft)
2. What is the low angle radiation pattern of an ideal
half wavelength dipole HF antenna installed
parallel to the earth? It is a figure-eight,
perpendicular to the antenna
3. The impedances in ohms at the feed point of the
dipole and folded dipole are, respectively: 73 and
300
Wire Antenna
1. A dipole transmitting antenna, placed so that the
ends are pointing North/South, radiates: mostly to
the East and West
2. How does the bandwidth of a folded dipole antenna
compare with that of a simple dipole antenna? It is
greater
3. What is a disadvantage of using an antenna
equipped with traps? It will radiate harmonics
4. What is an advantage of using a trap antenna? It
may be used for multi- band operation
5. What is one disadvantage of a random wire
antenna? You may experience RF feedback in
your station

Quad / Loop antenna

1. What is a cubical quad antenna? Two or more parallel four-
sided wire loops, each approximately one-electrical
wavelength long
2. What is a delta loop antenna? A type of cubical quad antenna,
except with triangular elements rather than square
3. The cubical "quad" or "quad" antenna consists of two or more
square loops of wire. The driven element has an approximate
overall length of: one wavelength
4. The delta loop antenna consists of two or more triangular
structures mounted on a boom. The overall length of the driven
element is approximately: one wavelength
5. Approximately how long is each side of a cubical quad antenna
driven element for 21.4 MHz? 3.54 metres (11.7 feet)
6. Approximately how long is each side of a cubical quad antenna
driven element for 14.3 MHz? 5.36 metres (17.6 feet)
7. Approximately how long is each leg of a symmetrical delta loop
antenna driven element for 28.7 MHz? 3.5 metres (11.5 feet)
Quad / Loops

1. Which statement about two- element delta loops and quad
antennas is true? They compare favorably with a three
element Yagi

2. Compared to a dipole antenna, what are the directional
radiation characteristics of a cubical quad antenna? The
quad has more directivity in both horizontal and
vertical planes

3. Moving the feed point of a multi-element quad antenna from
a side parallel to the ground to a side perpendicular to the
ground will have what effect? It will change the antenna
polarization from horizontal to vertical

4. What does the term "antenna front-to back ratio" mean in
reference to a delta loop antenna? The power radiated in
the major radiation lobe compared to the power
radiated in exactly the opposite direction