substrate permittivity effects on the performance of the micro strip elliptical patch antenna

Volume 2 No. 3 ISSN 2079-8407 Journal of Emerging Trends in Computing and Information Sciences

©2010-11 CIS Journal. All rights reserved.

http://www.cisjournal.org

Substrate Permittivity Effects on the Performance of the Microstrip Elliptical Patch Antenna

1B.T.P.Madhav, 1Prof.VGKM Pisipati, 1Dr.K.Sarat Kumar, 2P.Rakesh Kumar, 3K.Praveen Kumar, 1N.V.K.Ramesh, 4M.Ravi Kumar

1LCRC-R&D, Department of ECE, K L University, Guntur DT, AP, India 2Assistant professor, Department of ECE, LBRC (Autonomous) Engineering College, Mylavaram

3Associate Professor, Department of ECE, Vani School of Engineering, Cheviture 4Assistant professor, Department of ECE, Sri Saradhi Institute of Technology, Nuzvid

[email protected], [email protected]

ABSTRACT In this paper, the performance of a microstrip elliptical patch antenna is investigated using different substrate materials. The Microstrip antenna is studied with different substrates for a radiating elliptical patch of fixed dimensions. The effects of the dielectric constant of the perfect and lossy substrates on the resonant frequency, bandwidth and gain are investigated. A gain drop of 1.3 dB per decade is observed. Return loss, input impedance, radiation patterns and current distributions are investigated and presented with the help of Ansoft-HFSS. Keywords: Substrate permittivity, elliptical patch.

1. INTRODUCTION

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Substrate permittivity is one of the basic

parameter on which the antenna performance depends mostly. The substrate permittivity (εr) combined with the thickness h of a microstrip antenna affect the resonant frequency, gain, matching bandwidth and polarization. Microstrip antenna theory [1]-[5] indicates a degradation in performance when εr increases. High permittivity substrates reduce antenna size at the cost of the gain and matching bandwidth [6]-[9]. This study evaluates these parameters when antenna dimensions and resonant frequency of an elliptical patch (Fig. 1) are fixed. The evaluation is performed using the Finite Element Method from the commercial software Ansoft HFSS v.11. Air and other dielectric materials provided by HFSS, such as RT-duroid, FR4_Epoxy, Benzocylobuten, and Roger Ultrom200 are used to quantify the performance variations of the microstrip elliptical patch. A special nematic room temperature liquid crystal polymer material dielectric constant and dielectric loss tangent at microwave frequency is investigated and used in this present work along with the other materials.

The physical dimensions of the radiating element of the antenna are fixed. Using different substrate materials [10], the resonant frequency and the corresponding gain are evaluated. In HFSS some of the materials used are ideal, i.e., the loss tangent δ is zero, while others are lossy (δ > 0). This parameter is accounted for by evaluating the lossy materials with default δ not equal to zero, and as perfect dielectrics, with δ = 0. The effects of δ are also reported. Figure (1) shows the Ansoft generated model for the microstrip elliptical patch antenna.

Figure (1) Elliptical patch antenna

Table (1) Data table of the Antenna

Material εr Loss tangent

Return loss (dB)

Gain (dBi)

Air 1.0006 0 -7.8 5.30 RT-duroid 2.2 0.0009 -15.9 8.15 Roger ultrom 200

2.5 0.0019 -18.0 7.71

Benzocylobuten

2.6 0.0001 -19.5 7.828

Liquid crystal polymer

2.85 0.02 -17.5 6.6096

FR4 4.4 0.02 -29.2 3.2086

At the resonant frequency of 2.4GHz the

proposed antenna is designed with patch dimension along x-axis and y-axis of 43.8mm. substrate thickness of 1.59mm, substrate dimensions along x-axis and y-axis are 130mm. feed location along x-axis is 7.2mm and coaxial

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inner radius, outer radius and feed length of 1.04mm, 3.54mm and 10.4mm respectively.

2. RESULTS AND DISCUSSION

The return loss curves for elliptical patch antenna

with different substrate materials are shown in figure (2). Among all the substrate materials FR4 is giving minimum -29.8dB return loss and the Air substrate is giving maximum of -7.8dB. RT-duroid is giving -15.69dB, Roger-ultrom200 is giving -17.9dB, liquid crystal polymer is giving -17.12dB and benzocylobuten is giving the return loss of -19.23.

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Figure (2) Return loss curves, (2a) Air, (2b) RT-duroid5880, (2c) Roger-ultrom200 , (2d) Benzocylobuten, (2e) LCP (2f)

FR4

The driving point or feed point of an antenna is the location on an antenna where a transmission line is attached to provide the antenna with a source of microwave power. The impedance measured at the point where the antenna is connected to the transmission line is called the driving point impedance or input impedance. Figure (3) shows the input impedance smith chart curves for the elliptical patch antenna for different substrate materials. From the input impedance smith chart curve we obtained the rms and bandwidth for all the antennas of different substrate materials.

The rms obtained from all the substrates and their bandwidth ratios are listed in the below table (1)

Table (2) rms and bandwidth parameters

Substrate Material rms Bandwidth % Air 0.8122 83.54% RT-duroid 0.8226 88.56% Roger-ultrom200 0.8266 83.88% Benzocylobuten 0.8295 82% LCP 0.8095 78% FR4 0.7437 63%

From the table (2) it is clear that the RT-duroid is

giving the maximum bandwidth and FR4 substrate is giving lesser value. Form this point it is clear that the dielectric constant of lesser value is giving better bandwidth ratio in compared with the dielectric constant of higher value substrate material. Next to RT-duroid the Roger-ultrom200 is giving better bandwidth ratio and air substrate is very close to it.

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Figure (3) Input impedance smith chart, (3a) Air, (3b) RT-duroid5880, (3c) Roger-ultrom200

(3d) Benzocylobuten, (3e) LCP (3f) FR4

Figure (4) 3D-gain total, (4a) Air, (4b) RT-duroid5880, (4c) Roger-ultrom200 (4d) Benzocylobuten, (4e) LCP (4f) FR4

A maximum gain of 8.15dB is obtained by using

the RT-Duroid substrate and among all the substrate materials FR4 substrate material based antenna is giving less gain of 3.2dB. The gain in 3D and 2D representation




is given in the figure (4) and figure (5) for the elliptical antenna with different substrate materials.

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Figure (5) 2D-gain total, (5a) Air, (5b) RT-duroid5880, (5c) Roger-ultrom200 (5d) Benzocylobuten, (5e) LCP (2f) FR4

The radiation pattern of the antenna at phi=00 and

900 is given in the figure (6) and radiation pattern of antenna at theta=00 and 900 are shown in the figure (7). The liquid crystal substrate material used antenna is giving omni directional pattern in compared with the other materials and second to liquid crystal substrate the RT-duroid is giving appropriate radiation pattern among all the other materials. It is obvious from these results that the radiation pattern is acceptable for the all the substrate materials that we have chosen and the Liquid crystal polymer and the RT-duroid is giving better radiation pattern compared to other substrate materials.

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Figure (6) gain phi at 00 and 900, (6a) Air, (6b) RT-duroid5880, (6c) Roger-ultrom200

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Figure (7) gain theta at 00 and 900, (7a) Air, (7b) RT

duroid5880, (7c) Roger-ultrom200 (7d) Benzocylobuten, (7e) LCP (7f) FR4

Figure (8) Current distribution, (8a) Air, (8b) RT-

duroid5880, (8c) Roger-ultrom200 (8d) Benzocylobuten, (8e) LCP (8f) FR4

The current distribution of the proposed antenna

model on all the six substrate materials are given in the figure (8). It is observed that the RT-duroid, LCP and FR4 substrate materials based antenna is giving the mesh generation of more concentration around the patch. Which indicating the current distribution concentration at the radiating patch for these materials based antennas are




giving better results compared with the other substrate materials.

CONCLUSION

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Performance evaluation of the microstrip

elliptical patch antenna on different substrate materials with permittivity varying from 1.006 to 4.4 is simulated. A maximum gain of 8.15dB is obtained for the RT-duroid substrate used antenna in the present work. FR4 substrate based antenna is giving the least gain value 3.20dB for the proposed dimensional model. Similarly bandwidth of 88% achievement obtained in the case of RT-duroid, whereas by using FR4 only 63% is achieved. A gain drop of 1.3dB per decade is observed when going from dielectric constant of 1 to 4.4 for the substrate materials chosen. The loss tangent of substrate is also considered along with permittivity while simulating the present model.

[7] C.Y. Huang, & W. C. Hsia, “Planar Elliptical Antenna for Ultra wideband Communications,” Electronics Letters, vol. 41, 2005 pp. 296–297.

[8] “Effects of Substrate Permittivity on Planar Inverted-

F Antenna Performances” Yves -Thierry Jean-Charles, JOURNAL OF COMPUTERS, VOL. 4, NO. 7, JULY 2009.

[9] “Microstrip Patch Antenna Design Using Artificial

Material Loadings” I. Calafell, P.J. Ferrer, J.M. González-Arbesú and J. Romeu, journal of applied engineering research, vol-2, feb-2004.

[10] A. D. Yaghjian, S. R. Best, “Impedance, bandwidth,

and Q for antennas”, IEEE Tran. Antennas Propag. vol. 53, no. 4, pp. 1298-1324, April 2005.

ACKNOWLEDGMENTS

The authors like to express their thanks to the

department of ECE and management of K L University for their support and encouragement during this Research work.

Author’s Details:

REFERENCES

[1] Constantine A. Balanis; Antenna Theory, Analysis

and Design, John Wiley & Sons Inc. 2ndedition. 1997.

B.T.P.Madhav was born in India, A.P, in 1981. He received the B.Sc, M.Sc, M.Tech, MBA degrees from Nagarjuna University, A.P, India in 2001,

2003, 2007, 2009 respectively. From 2003-2007 he worked as lecturer and from 2007 to till date he is working as Asst.professor in Electronics Engineering. He has published more than 25 papers in International and National journals. His research interests include antennas, liquid crystals applications and wireless communications.

[2] Y.T. Lo. and S.W. Lee, editors, Antenna Handbook

Theory, Applications and Design, Van Nostrand Reinhold Company, New York, 1988.

[3] Stutzman Warren L. and Thiele Antennas and

propagation Magazine, vol.52, Feb 2010) [4] Broadband Microstrip Antennas, Girish Kumar and

K. P. Ray, Artech House, 2002. [5] Daniel H. Schaubert, “A review of Some Microstrip

Antenna Characteristics” Microstrip Antennas - The Analysis and Design of Microstrip Antennas and Arrays, edited by David M. Pozar, Daniel H. Schaubert, John Wiley & Sons, Inc., 1995, ISBN 0-7803-1078-0.

Prof. VGKM Pisipati was born in India, A.P, in 1944. He received his B.Sc, M.Sc and PhD degrees from Andhra University. Since 1975 he has been

with physics department at Acharya Nagarjuna University as Professor, Head, R&D Director. He guided 22 PhDs and more than 20 M.Phils. His area of research includes liquid crystals, nanotechnology and liquid crystals applications. He visited so many countries and he is having more than 260 International research publications. He served different positions as academician and successfully completed different projects sponsored by different government and non-government bodies. He is having 5 patents to his credit.

[6] A Derneryd, “Linearly Polarized Microstrip

Antennas”, IEEE Trans. Antennas and Propagation, AP-24, pp. 846-851, 1976.

substrate permittivity effects on the performance of the micro strip elliptical patch antenna

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