International Journal of Engineering and Technical Research (IJETR)

ISSN: 2321-0869, Volume-2, Issue-3, March 2014

Design of a Novel Microstrip Patch Antenna for

Microwave Imaging Systems
Magthoom Fouzia Y, Dr.K.Meena alias Jeyanthi

Abstract- A novel compact bowtie antenna is designed and

optimized with rounded edge for microwave imaging
applications such as cancer tissue detection. The proposed
antenna is designed using FR4( =4.8) as a substrate material
to operate in 5.8 GHz. The proposed microstrip patch antenna
is a low profile, low cost and minimal weight that are capable to
maintain its high performance over a wide range of
frequencies. By designing such an antenna, it is possible to
achieve a return loss of -29.62 dB at gain of 6.2dB and good
radiation characteristics compared to conventional antennas.
The parameters are optimized using ADS simulation software.

Index Terms- Microstrip antenna, Return Loss, Radiation

Pattern, Microwave Imaging.

I. INTRODUCTION
Microwave Imaging in medical field is one of the Figure 1: Experimental setup of Microwave Imaging
important diagnosing mechanisms available. This System
technique uses non destructive evaluation of biological tissue
based on the dielectric property changes. Therefore Microwave imaging can be defined as seeing the internal
microwave imaging can be used as a diagnostic tool. Several structure of an object by illuminating the object with low
applications of microwave imaging have been proposed in power electromagnetic fields at microwave frequencies. An
the medical field and one of them is microwaves for breast antenna is used to illuminate the object with microwaves
cancer detection. which travels through the object and is then detected with the
Many women, especially young ones have receiver antenna. One of the key system components is the
radiographically dense breasts. Which means that the breast antenna, as it must effectively radiate and receive the signal
tissues contain more glands and ligaments resulting in dense from the object being imaged. Several UWB antenna designs
breast tissue. Thus the diagnosis becomes very difficult. In have been proposed for use in medical imaging systems.
order to exclude the difficulties encountered alternative Some of the proposed antennas have non-planar structure
techniques like magnetic resonance imaging with contrast while others have low gain and poor return loss. Majority of
enhancement and ultrasound imaging are used. the compact UWB antenna presented in literature exhibit
The fundamental basis of any imaging system lies in the Omni-directional radiation patterns with relatively low gain.
contrast that exists between the properties of healthy and These types of antennas are suitable for the short range
malignant tissues. Breast cancer detection with indoor and outdoor communication. However, for radar
mammography basically utilizes a low dose X-ray as the systems, such as microwave imaging systems for detection of
initial diagnostic tool. Frequent exposures to X-rays of any tumor in womens breast a moderate gain antenna is
kind are really not recommended for young people. Statistics preferred. Among few alternatives, a microstrip antenna was
in this field suggests that there is a false positive cases exists chosen due to the low profile and ease of fabrication and can
one in five cases in women.. Based on National Council on be used in a planar gap coupled array configuration for
Radiation Protection (NCRP) and International Radiation imaging applications. The conventional microstrip antenna
Protection Association (IRPA) suggestions, human exposure suffers from a major disadvantage that it has a narrow
at or below the permissible levels recommended by IEEE and bandwidth. Over the years, there have been several research
other organizations is not harmful to human health. The efforts by various groups worldwide aiming to increase the
experimental setup of microwave imaging is depicted in fig1. bandwidth of these antennas.

Manuscript received March 17, 2014. II. ANTENNA DESIGN

Magthoom Fouzia Y, PSNA College of Engineering and Technology,
Dindigul, Tamil Nadu, India. A. Construction of Conventional Bowtie Antenna
Dr.K.Meena alias Jeyanthi, PSNA College of Engineering and Microstrip patch antenna consists of a radiating patch on
Technology, Dindigul, Tamil Nadu, India. one side of a dielectric substrate with a continuous metal

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 Design of a Novel Microstrip Patch Antenna for Microwave Imaging Systems

layer bonded to the opposite side of the substrate which forms the angle between the side lengths of the triangles. The value
a ground plane. The patch is generally made of conducting of a can be calculated as follows
material such as copper or gold and can take any possible (1)
shape(conventional types are square, rectangle, circle and
triangle). A patch antenna is a narrowband, wide-beam (2)
antenna fabricated by photo etching the antenna element Where
pattern in metal trace on the dielectric substrate[11]. The a- side length of Bowtie
recent studies of microstrip patches revealed that the - Effective Side length of Bowtie
triangular patch has a radiation characteristic similar to a - Resonance Frequency
rectangular patch, but with reduced dimensions. The - Dielectric Constant
principle of transmission line model of triangular microstrip
antenna is depicted in the fig 2. Fig 4 shows the return loss of the conventional triangular
bowtie antenna on FR4 substrate showing its deep in - 9.9dB
with its center frequency as 6GHz

m1
indep(m1)= 6.135E9
plot_vs(dB(S(1,1)), freq)=-9.924
Valley
2

-2

dB(S(1,1))
-4
Figure 2: Principle of Transmission Line Model
-6

-8

m1
-10
4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0

freq, GHz

.
Figure 5: Return Loss of conventional triangular structure

The Antenna parameters of the conventional triangular

Bowtie Antenna is shown in table 1.

Conventional Triangular
Antenna Parameters
Bowtie Antenna

Power Radiated(Watts) 2.48714e-07

Effective Angle(Steradians) 4.43402

Figure 3: Construction of Conventional Triangular Bowtie Directivity(dB) 4.52412

Antenna Maximum Intensity(Watts/Steradian) 5.60922e-08
Angle of U max(Theta,phi) (50,180)
R E(Theta)max(mag,Phase) (0.00538819,177.004)
1 2
E(Phi)max(mag,Phase) (0.0036374,-90.0455)
R XL L
E(x)max(mag,Phase) (0.00346346,-2.99579)
1 21 2 1 2
E(y)max(mag,Phase) (0.0036374,89.9545)
C
1 2 E(z)max(mag,Phase) (0.00412759,-2.99759)

Return Loss(dB) -9.94

0
Table 1:Parameters of conventional triangular Bowtie
0 Antenna

Figure 4: Electrical Model of Triangular Patch

B. Construction of Modified Square Bowtie Antenna

Fig.3 shows the bowtie Antenna dimensions with The modified Bowtie strip is square in shape instead of
coordinates. a is the side length of the bowtie strip, is triangular structure A modified version of Conventional

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 International Journal of Engineering and Technical Research (IJETR)
ISSN: 2321-0869, Volume-2, Issue-3, March 2014
triangular Bowtie Antenna and its construction is shown in
fog 6.
III. PROPOSED ANTENNA DESIGN
The conventional microstrip bow-tie antenna consists
of two triangle patches disposed on the planar structure to
form a shape of bowtie. The proposed system improves the
performance of the conventional Bowtie Antenna by adding
the rounded corners on the radiation surfaces.
The electrical model of the proposed bowtie structure is
shown in fig 8.

R1 R2
1 2 1 2

L1 L2
1 2 1 2

C1 C2
Figure 6: Modified Square Bowtie Antenna 0 1 2 1 2 0

The effective width of the Bowtie arm is given by[12],

(3) 2
2
2

R3 L3 C3
The actual length is determined as follows:
1 1
(4) 1

The equation 5 can be used to determine the input

impedance of the microstrip Patch

0
(5)
Figure 8: Electrical model of proposed structure

Where R is the resonant resistance of the resonant An electrical model was developed for analyzing this
parallel RLC circuit, fr is the resonant frequency, and QT is antenna which was inspired from the electrical model of the
the total quality factor associated with the system losses triangular patch described in [3].The transmission line was
including radiation, the loss due to heating in conducting modeled by RLC circuit. The RLC parameters were
elements and ground plane, and the loss due to heating in the determined by means of the formula developed in section 2.
dielectric medium.
The impedance of the air filled microstrip line is as follows
(6)
The return loss(-12.7dB) of modified square Bowtie Antenna
shows its better performance compared to conventional
triangular patch(fig .7).

m1
indep(m1)= 6.719E9
plot_vs(dB(S(1,1)), freq)=-12.760
Valley
2

-2

-4
Figure 7: Modified rounded Bowtie Structure
dB(S(1,1))

-6

-8

-10 IV. RESULTS AND DISCUSSION

-12 m1 The rounded bowtie Antenna was designed on a FR4
-14 substrate of thickness 1.6mm. The Dimensions list is given in
4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 the below Table:
freq, GHz

Figure 7: Return Loss of Modified square Bowtie structure

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 Design of a Novel Microstrip Patch Antenna for Microwave Imaging Systems

Dielectric constant of the substrate( ) 4.8

Thickness of the substrate(mm) 1.6
Antenna Modified Modified
Length of the Arm(mm) 10 Parameters Square Bowtie Rounded Bowtie
Width of the Arm(mm) 11 Antenna Antenna
Length of the feed(mm) 11
Width of the Feed(mm) 1 Power 1.96117e-05 2.1405e-05
Radiated(Watts)
Effective 2.95272 3.02569
Table 2: Dimensions of the rounded bowtie Antenna Angle(Steradians)
Directivity(dB) 6.28988 6.18385
To characterize the performance of the antenna, the Maximum 6.64191e-06 7.07442e-06
following measures are considered: Intensity(Watts/Sterad
ian)
1. Return Loss Angle of U (0,0) (0,0)
2. Gain of the Antenna max(Theta,phi)
3. Radiation pattern at the center frequency E(Theta)max(mag, (0.0500189,8 (0.0595775,8
Phase) 2.1699) 2.1148)
The return loss of rounded bowtie is -29.6dB which is very E(Phi)max(mag,Ph (0.0500253,8 (0.0421998,8
ase) 2.1709) 2.1669)
good compared to the previous designs at its center E(x)max(mag,Phas (4.57942e-06, (0.0016702,-9
frequency. The S11 graph is seen in fig.8 and the radiation e) -96.2711) 6.7948)
pattern is shown in fig.9. E(y)max(mag,Phas (0.0707419,8 (0.0729898,8
e) 2.17) 2.1316)
E(z)max(mag,Phas (0,-180) (0,-180)
m2
indep(m2)= 5.667E9 e)
plot_vs(dB(S(1,1)), freq)=-29.623 Return Loss(dB) -12.76 -29.623

0 V. CONCLUSION
-5
dB(S(1,1))

-10
In this Paper, a modified, compact bowtie antenna was
-15
designed and simulated and compared with the existing
-20 conventional patches. The results show that the proposed
-25 antenna provides a return loss of -29dB at 5.8GHz which
m2
-30 would be best suited for microwave imaging systems.
4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0

freq, GHz

REFERENCES
Figure 8: Return Loss of rounded bowtie Antenna

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 International Journal of Engineering and Technical Research (IJETR)
ISSN: 2321-0869, Volume-2, Issue-3, March 2014
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