Analysis of Coaxial Feeding and Strip Line Feeding on the

Performance of the Square Patch Antenna

1B.T.P.Madhav, 1J.Chandrasekhar Rao, 1K.Nalini, 2N.Durga Indira

1 Assistant professor, Department of ECE, K L University, AP, India 2M.Tech Project Student, Department of ECE, K L University, AP, India

Abstract:

Microstrip patch antennas have different feeding

techniques. They can be divided based on power

transfer mechanism from feed line to patch. This

paper focuses on the design, model and simulation of

a microstrip patch antenna by applying two well

known and mostly used feeding techniques. Those

are coaxial feeding and the strip line feeding. The

proposed antenna is excited through these two

feeding techniques and the antenna design has been

executed and simulated using Ansoft’s HFSS.

Comparative study of simulated parameters like gain,

Bandwidth, directivity, Radiation pattern have been

done and presented in this paper.

1. Introduction:

Microstrip patch Antennas has various advantages

such as low profile, light weight, easy fabrication.

Feed line is used for excite to radiate by direct or

indirect contact. Microstrip patch antennas can be fed

in a variety of ways.1.Contacting 2.Non-Contacting.

In contacting method the RF power is fed directly to

the radiating patch using a connected element, they

are microstrip feed and coaxial feed.

In Non Contacting method, electromagnetic coupling

is done to transfer the power between the feed line

and the radiating patch, they are Aperture coupled

feed and Proximity coupled feed.

2. Feeding Techniques:

Microstrip line feed is one of the easier methods to

fabricate as it is a just conducting strip connecting to

the patch and therefore can be consider as extension

of patch. It is simple to model and easy to match by

controlling the inset position. The disadvantage of

this method is that as substrate thickness increases,

surface wave and spurious feed radiation increases

which limit the bandwidth.

In Coaxial feeding, the inner conductor of the coaxial

is attached to the radiation patch of the antenna while

the outer conductor is connected to the ground plane.

The main advantages of this method are easy to

fabricate, easy to match and low spurious radiation.

Aperture coupling consist of two different substrate

separated by a ground plane. On the bottom side of

lower substrate there is a microstip feed line whose

energy is coupled to the patch through a slot on the

ground plane separating two substrates. Top substrate

uses a thick low dielectric constant substrate, and the

bottom substrate uses high dielectric substrate. The

ground plane, which is in the middle, isolates the feed

from radiation element and minimizes interference of

spurious radiation for pattern formation and

polarization. The main advantage of this method is

allows independent of feed mechanism element.

Proximity coupling has the largest bandwidth, has

low spurious radiation. Length of feeding stub and

width-to-length ratio of patch is used to match.

Figure (1) coaxial feeding square patch antenna

B.T.P.Madhav et al, Int. J. Comp. Tech. Appl., Vol 2 (5), 1352-1356

IJCTA | SEPT-OCT 2011 Available online@www.ijcta.com

1352

ISSN:2229-6093

Figure (2) Strip line feeding square patch antenna

Figure (1) shows the coaxial feeding microstrip

square patch antenna and Figure (2) shows the strip

line feeding microstrip square patch antenna. Both

these antennas are using RT-duroid substrate material

of dielectric constant 2.2.

3. Results and analysis

1.50 2.00 2.50 3.00 3.50 4.00 4.50 5.00 5.50Freq [GHz]

-30.00

-25.00

-20.00

-15.00

-10.00

-5.00

0.00

dB

(St(

1,1

))

Ansoft Corporation Patch_Antenna_ADKv1Return Loss

m 1

Curve Info

dB(St(1,1))Setup1 : Sw eep1

Name X Y

m1 3.4085 -27.5877

Figure (3a) Return loss Vs Frequency curve for

coaxial feeding antenna

The return loss curve for the square patch antenna by

using coaxial feeding is presented in figure (3a). The

operating frequency of the proposed antenna is

chosen at 3.4GHz which is used for the Wi-Fi

connectivity. From the figure (3a) we got the return

loss of -25.58dB at 3.4GHz.

The figure (3b) showing the return loss curve for the

square patch antenna designed using microstrip line

feeding. The return loss obtained from this curve is

about -14.15dB at 3.4GHZ.

1.50 2.00 2.50 3.00 3.50 4.00 4.50 5.00 5.50Freq [GHz]

-35.00

-30.00

-25.00

-20.00

-15.00

-10.00

-5.00

0.00

dB

(St(

1,1

))

Ansoft Corporation Patch_Antenna_ADKv1Return Loss

m1

Curve Info

dB(St(1,1))Setup1 : Sw eep1

Name X Y

m1 3.4085 -14.1512

Figure (3b) Return loss Vs Frequency curve for

microstrip line feeding antenna

From the both the results of return loss for coaxial

feeding and strip line feeding we observed that a

considerable values obtained from both the cases

which is showing return loss less than -10dB. For the

coaxial feeding we go better result in compared with

the strip line feeding as per the return loss is

concerned.

0.20 0.40 0.60 0.805.002.001.000.500.20

5.00

-5.00

2.00

-2.00

1.00

-1.00

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-0.50

0.20

-0.20

0.00-0.005.00 2.00 1.00 0.50 0.20

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708090100110120

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180

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-110-100 -90 -80

-70-60

-50

-40

-30

-20

-10

Ansoft Corporation Patch_Antenna_ADKv1Input ImpedanceCurve Info rms bandw idth(1, 0)

St(1,1))Setup1 : Sw eep1 0.7600 3.0391

Figure (4a) Input Impedance curve for coaxial

feeding antenna

Figure (4a) is giving the input impedance smith chart

for the square patch antenna operating at 3.4GHz.

The rms obtained from the coaxial feeded square

patch antenna is 0.766 and bandwidth enhancement

for this model is about 0.89%.

Figure (4b) is showing impedance matching curve of

the proposed antenna with strip line feeding. The rms

obtained for this case is about 0.7668 and the

bandwidth enhancement is about 0.91%.

B.T.P.Madhav et al, Int. J. Comp. Tech. Appl., Vol 2 (5), 1352-1356

IJCTA | SEPT-OCT 2011 Available online@www.ijcta.com

1353

ISSN:2229-6093

0.20 0.40 0.60 0.805.002.001.000.500.20

5.00

-5.00

2.00

-2.00

1.00

-1.00

0.50

-0.50

0.20

-0.20

0.00-0.005.00 2.00 1.00 0.50 0.20

5.00

-5.00

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1.00

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10

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708090100110120

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180

-170

-160

-150

-140

-130-120

-110-100 -90 -80

-70-60

-50

-40

-30

-20

-10

Ansoft Corporation Patch_Antenna_ADKv1Input ImpedanceCurve Info rms bandw idth(1, 0)

St(1,1))Setup1 : Sw eep1 0.7658 3.0995

Figure (4b) Input Impedance curve for micro strip

line feeding antenna

From these results we noticed that the rms and

bandwidth is higher for strip line feeding in

compared with the coaxial feeding.

-200.00 -150.00 -100.00 -50.00 0.00 50.00 100.00 150.00 200.00Theta [deg]

-30.00

-25.00

-20.00

-15.00

-10.00

-5.00

0.00

5.00

10.00

Y1

Ansoft Corporation Patch_Antenna_ADKv1ff_2D_GainTotalm1m2 Curve Info

dB(GainTotal)Setup1 : LastAdaptive

dB(GainTotal)_1Setup1 : LastAdaptive

Name X Y

m1 0.0000 8.4059

m2 4.0000 8.4713

Figure (5) gain of the antenna for coaxial and strip

line feeding

Figure (5) showing the gain of the antenna by using

the coaxial and strip line feeding mechanism. For the

coaxial feeded microstrip square patch antenna a gain

of 8.47dBi is obtained and for the strip line feeding a

gain of 8.40dBi is obtained. From figure (5) we can

conclude that the gain for the current model by using

both the feeding mechanisms is almost equal. The

difference in the gain between these two cases is

about 0.0654dB.

Figure (6a) Radiation pattern in phi direction for

coaxial feeding antenna

Figure (6a) giving the radiation pattern of the coaxial

feeded antenna in three dimensional view. For each

mode there are two orthogonal planes in the far-field

region. One designated as E-plane and other

designated as H-plane. The far-zone electric field lies

in the E-plane and the far-zone magnetic field lies in

the H-plane. The patterns in these planes are referred

to as the E and H plane patterns respectively.

Figure (6b) Radiation pattern in phi direction for

microstrip line feeding antenna

For the TM01 mode the contributions to the far fields

are from the magnetic surface current densities on the

side walls containing the radiating edges. The

direction of magnetic currents that the E-plane is the

y-z plane (Phi=900) and the H-plane is the x-z plane

(Phi=00). Fig (6a) and fig (6b) are giving radiation

pattern in phi direction for coaxial feeded and strip

line feeded antennas.

B.T.P.Madhav et al, Int. J. Comp. Tech. Appl., Vol 2 (5), 1352-1356

IJCTA | SEPT-OCT 2011 Available online@www.ijcta.com

1354

ISSN:2229-6093

Figure (7a) Radiation pattern in Theta direction for

coaxial feeding antenna

Figure (7b) Radiation pattern in Theta direction for

microstrip line feeding antenna

Figure (7a) and figure (7b) are giving the radiation

pattern in theta direction for both the cases in three

dimensional views. From these two figures we

observed that the radiation pattern is broader in both

directions and the radiation efficiency is acceptable

for the entire region.

1.50 2.00 2.50 3.00 3.50 4.00 4.50 5.00 5.50Freq [GHz]

0.00

10.00

20.00

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90.00

100.00

VS

WR

t(co

ax_

pin

_T

1)

Ansoft Corporation Patch_Antenna_ADKv1XY Plot 1

m 1

Curve Info

VSWRt(coax_pin_T1)Setup1 : Sw eep1

Name X Y

m1 3.4940 1.4114

Figure (8a) VSWR Curve for coaxial feed antenna

Figure (8a) and figure (8b) giving the VSWR curve

Vs frequency for both the feeding techniques. The

VSWR obtained from the coaxial feeded square patch

antenna is about 1.414 and for the strip line feeded

antenna the VSWR is 1.441 at 3.4 GHz. Both these

values are maintaining the standardization with 2:1

VSWR ratio.

1.50 2.00 2.50 3.00 3.50 4.00 4.50 5.00 5.50Freq [GHz]

0.00

10.00

20.00

30.00

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90.00

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VS

WR

t(co

ax_

pin

_T

1)

Ansoft Corporation Patch_Antenna_ADKv1XY Plot 1

m 1

Curve Info

VSWRt(coax_pin_T1)Setup1 : Sw eep1

Name X Y

m1 3.4940 1.4413

Figure (8b) VSWR Curve for strip line feed antenna

S.NO Antenna

parameters

Coaxial

feeding

Microstrip line

feeding

1 Max U 0.0061713 w/sr 0.0056694 w/sr

2 Peak Directivity 7.0357 7.1399

3 Peak gain 7.0328 7.1268

4 Peak realized gain 7.0128 6.7931

5 Radiated power 0.011023w 0.0099786w

6 Accepted power 0.011027w 0.0099969w

7 Incident power 0.011059w 0.010488w

8 Radiation efficiency

0.9996 0.99816

9 Front to back ratio 110.15 112.81

Table (1) Antenna Parameters

Maximu

field data

values

Coaxial feeding Microstrip line feeding

rE field Value

(v)

At Phi

(deg)

At

Theta

(deg)

Value

(v)

At

Phi

(deg)

At

Theta

(deg)

Total 2.1571 90 4 2.0676 90 4

X 0.8345 20 32 0.2736 25 32

Y 2.1519 90 4 2.0625 90 4

Z 0.9649 90 42 0.91348 90 42

Phi 2.1409 180 0 2.0538 180 0

Theta 2.1571 90 4 2.0675 90 4

LHCP 1.563 150 12 1.476 140 8

RHCP 1.5625 30 10 1.4784 40 8

Table (2) Maximum field data

B.T.P.Madhav et al, Int. J. Comp. Tech. Appl., Vol 2 (5), 1352-1356

IJCTA | SEPT-OCT 2011 Available online@www.ijcta.com

1355

ISSN:2229-6093

Conclusion:

The proposed square patch antenna is designed by

considering coaxial feeding and strip line feeding and

their output parameters are presented in this paper. In

both the cases the results showing the good

impedance matching between the input and the

output. The gains obtained from these cases are

8.40dBi and 8.47dBi respectively for coaxial feeding

and strip line feeding. The other antenna parameters

and maximum field data is shown in table (1) & table

(2) which are almost identical to each other. The strip

line feeding is preferable because of impedance

mismatching with the case of coaxial feeding.

Coaxial feeding requires number of trial and error

methods for getting impedance bandwidth perfectly.

Whereas for the strip line feeding impedance related

problems can be almost avoided.

Acknowledgements:

The authors like to express their thanks to

the management of K L University and the

Department of Electronics and Communication

Engineering for their continuous support and

encouragement during this work.

References:

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P.Rakesh Kumar, N.V.K.Ramesh, B.Nagaraju Nayak,

Comparative Analysis of Shorting Pin and Shorting Plate Models

for Size Reduction in the Microstrip Patch Antennas,

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8504; e-ISSN-2230-8512Vol 02, Issue 04; July 2011

[2] B.T.P.Madhav, K.V.L.Bhavani, P.Poorna Priya, Y.Joseph

Manoj Reddy, N.Srinivas Sri Chaitanya, N.Krishna Chaitanya,

ANALYSIS OF ORTHOGONAL FEED DUAL FREQUENCY

RECTANGULAR MICROSTRIP PATCH ANTENNA FOR S-

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[3] P.J.Soh, M.K.A.Rahim, A.Asrokin & M.Z.A.Abdul Aziz,

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Author’s Details:

B.T.P.Madhav was born in India, A.P, in

1981. He received the B.Sc, M.Sc, MBA, M.Tech degrees

from Nagarjuna University, A.P, India in 2001, 2003, 2007,

and 2009 respectively. From 2003-2007 he worked as

lecturer and from 2007 to till date he is working as

Assistant Professor in Electronics Engineering. He has

published more than 45 papers in International and

National journals. His research interests include antennas,

liquid crystals applications and wireless communications.

J. Chandrasekhar Rao was born in India,

A.P in 1985. He received his B. Tech, M.Tech degrees in

ECE. He currently working as Assistant professor in ECE

department of K L University. He has 3 national and 1

International conference paper, and one international

journal paper. His research interests include satellite

communications, antennas, and image processing.

B.T.P.Madhav et al, Int. J. Comp. Tech. Appl., Vol 2 (5), 1352-1356

IJCTA | SEPT-OCT 2011 Available online@www.ijcta.com

1356

ISSN:2229-6093