INTERNATIONAL JOURNAL OF ELECTRICAL, ELECTRONICS AND COMPUTER SYSTEMS (IJEECS), Volume 1, Issue 2, April 2011. ISSN: 2221-7258(Print) ISSN: 2221-7266 (Online) www.ijeecs.org

Physical Insight Into The Gain and Bandwidth Enhancement of U Type Microstrip Patch with Air Substrate A. Suman, R. K. Mistry, N. N. Dutta, P. Chatterjee, S. Chattopadhyay

Abstract— A simple and novel U type microstrip patch antenna with air substrate is proposed and thoroughly investigated. It shows appreciable enhancement in gain (about 11 dBi) along with significant improvement in bandwidth (about 10%) compared to conventional microstrip patch. The physical reason for such improvement in gain and bandwidth is thoroughly explained.Simulated electric field distribution on the entire antenna structure is also presented to explain such behavior of the proposed antenna. Index Terms— Bandwidth, Gain, Microstrip Antenna

1 INTRODUCTION

M

ICROSTRIP patch antennas are gaining popularity day by day. It has wide scope in wireless and mobile communication systems. A microstrip patch antenna is a low profile antenna and has several advantages over conventional antenna. A conventional rectangular patch antenna etched on a grounded substrate give 4-5% bandwidth and around 5-6 dBi gain. Larger gain is always a positive requirement, but broader impedance bandwidth along with high gain is very promising in the field of patch antenna. Different techniques have been reported to increase the bandwidth and reduce the size of microstrip patch antennas such as increasing the thickness of dielectric substrate, decreasing dielectric constant [1], slot-loading [2], feed modification [3], chip loading [4], stacked shorted patch [5], using parasitic patches [6]. But none of the above has investigated for its gain. One recently reported structure [7] proposed that the microstrip antenna with conical horn gives high gain like 11 dBi but with poor band width (6%). Similarly in [8], microstrip with sandwitched substrate is presented which show excellent band width but with poor gain (5.2 dBi). Another reported work [9] gives high gain by using microstrip antenna array and 12 dBi gain is observed as expected. Using negative capacitor with a chip resistor incorporated in rectangular micro-

strip antenna the gain can be enhanced to 9.2 dBi as reported in [10]. Some analysis with broadband microstrip antenna is found in open literature [11] and in very recently reported work [12], it is proposed that the gain of microstrip antenna can be enhanced using air as substrate and the gain enhancement factor is successfully estimated. One recently reported work [13] dealt with inverted U type patch which gives improved gain (≈ 7.5 dBi gain) and appreciable bandwidth (around 7 %). However, if the slot has been introduced centrally on the conventional rectangular patch it will give birth to another structure which is referred as U type patch antenna and a significant improvement in the gain and bandwidth are achieved simultaneously. In this paper, we have demonstrated the reason for improvement in gain and impedance bandwidth of the proposed patch on the air substrate. We have attempted to increase the gain and bandwidth all together by changing the patch geometry and substrate type. The entire antenna structure is very lightweight and compact as opposed to several other suggested structures.

2 ANTENNA GEOMETRY

The antenna geometry is shown in Fig. 1. A single slot of 6 mm x 6 mm has been introduced to give a U shape patch with air as a substrate. The ———————————————— detailed dimension of the patch is shown in Fig.  A.Suman,R.K.Mistry,N.N.Dutta,P.Chatterjee,S.Chattopadhyay are 1(a). In the present investigation, a 0.1 mm thin with the Department of Electronics and Communication Engineering, Siliguri Institute ofTechnology, P.O:Sukna, Siliguri,District:Darjeeling, metal strip (copper with permeability 1) held at 1.575 mm height above the ground plane. The PIN:734009,West Bengal,India.Common Research Group Mail:[email protected]

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patch is soldered with the probe and thus no additional support or spacer is required to hold it.

3 RESULTS AND DISCUSSIONS The introduction of single slot in rectangular patch in order to develop a U type microstrip antenna results in discontinuity in the structure. Following Ang and Chuang [16], as slot width increases (AB portion increases) inductive effect increases. For the dominant TM10 mode the magnetic field H is maximum in the central region. As a result the electric surface current

Js

is maximum in that region, because we know that

J s  nˆ  H

, where

nˆ is

the outward normal to

the patch surface.

So, a lot of surface current is developed through edge AB which stores magnetic energy intensely in that region. As a result it simulates inductance. But this will not effect dominant TM10 mode as L1 is not equal to λ/2, instead it is λ/4 for the same mode. But for next higher mode ABJI portion of the patch will be acting as λ/2 resonant patch as its frequency is doubled. So for that portion of the patch structure will try to excite next higher order mode ie, TM20 below ABJI portion of the patch. At the same time, for that higher mode AB portion offers more inductive reactance as discussed above and as a result resonance frequency of next higher order mode decreases from its natural value. Actually the resonant frequency

fr 

1

where L and C are the

LC

equivalent inductance and capacitance developed due to patch structure. Thus the two frequencies i.e. dominant and next higher order mode come closer which may be attributed for higher impedance bandwidth for this proposed structure.The simulated results obtained for the prototypes employing different configuration of patches over the air substrate are presented. In Fig. 2, the return loss profile of the prototype is shown using [14]. The proposed antenna shows around 10 % of impedance bandwidth which is 5% more than the conventional one. Now if we increase AB portion more than GH and CD portions become too less. So, the radiation due to dominant mode which is actually through the above regions decreases. This will affect the peak gain of the overall antenna

system. In this way, we have conceived an optimum structure where gain and bandwidth are good together. The bandwidth of the proposed antenna works in the range of (10.34-11.27) GHz. Fig. 3 shows the radiation pattern of the proposed antenna. Around 11 dBi gain is observed. The E-plane cross-polarized fields for both kind of antenna appear to be almost identical. But the proposed antenna results in comparatively higher cross-polarized radiation, which may be 5-6 dB larger around ± 45 degrees compared to those due to conventional rectangular microstrip antenna. It is also observed that as we increase the slot width, bandwidth of the antenna increases at the cost of gain. The physical insight in to obtaining high gain as well as broader impedance bandwidth performance of the proposed antenna has been explored using simulated electric fields distributed over the substrate. Those are shown in Fig. 4. A comparative observation between Fig. 5 (a) and 5 (b) indicate that the electric field in the substrate distributed over wider area as soon as the structure changes from conventional to the new structure. Moreover, the electric field distribution around the patch is uniform in the new structure than the conventional one. This in fact, indicate additional effective radiating aperture in case of proposed antenna compared to conventional rectangular patch antenna. We know that gain of an antenna:

G   ap

4Aeff

ciency and

2

Where

 ap

is aperture effi-

Aeff is effective radiating aperture.

As in our proposed structure, electric field is distributed more uniformly rather than that for conventional microstrip antenna, the aperture efficiency is much more for our proposed antenna. These may be attributed for high gain values for the proposed antenna. Now, we may concentrate on the change in impedance bandwidth value. The electric field distribution over the wide area in the substrate corroborates lower effective dielectric constant for our new structure than the conventional microstrip patch which in turn improves the impedance bandwidth for proposed antenna.

4 CONCLUSION The physical insight for higher gain and bandwidth of the proposed antenna has been presented. The proposed antenna finds wide application in wireless and mobile applications where appreciable value of gain and bandwidth are required. The microstrip antenna introduces new

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generation of communication with enhanced speed, improved communication channel capacity and large area coverage at a very reasonable price which is sufficient to fulfill the upcoming challenge. It can be predicted that further research in this direction can result in a breakthrough in mobile communication technology.

REFERENCES [1]. Ramesh Garg, Prakash Bartia, Inder Bhal and Apsiak Ittipiboon, “Microstrip Antenna Design Hand Book,” Artech House,Norwood, MA, 2001. [2]. A. A.Eldek, , A. Z. Elsherbeni, and C.E.Smith, “Characteristics of BOW-TIE Slot Antenna with Tapered Tuning Stubs for Wideband Operation,” Process In Electromagnetics Research, PIER 49, 53- 69, 2004. [3]. Y.Ge, , K. P. Essele, and T. S. Bird, “A Broadband Eshaped Patch Antenna with a Microstrip Feed,” Microwave & Opt Tech. Letter, vol. 42, No. 2, July20, 2004. [4]. K. L. Wong, and Y. F. Lin, “Microstrip-Line-Fed Compact Broadband Circular Microstrip Antenna with Chip Resistor Loading,” Microwave Opt. Techno. Lett., vol. 17, 53-55, Jan. 1998. [5]. R. B Waterhouse,. “Broadband Stacked Shorted Patch,” Electronic Letters, vol. 35, 98-100, Jan. 21, 1999. [6] D.M.Pozzar, “Microstrip Antenna Coupled to Microstripline,” Electron lett., vol.21, no.2, pp. 49-50, Janurary 1995. [7] Pramod Kumar, Deepak Batra, A. K. Shrivastav, “High Gain Microstrip Antenna Capacitive Coupled To a Square Ring with Surface Mounted Conical Horn,” International Journal of Electronics and Communication Technology, vol. 1,issue.1, December 2010. [8] Nasimuddin, Z.N.Chen, “Wideband Microstrip Antennas with Sandwich Substrate,” IEE Proc. Microwaves, Antennas & Propagation, vol.2, issue. 6, pp. 538540, 2008. [9] C. Karnfelt, P. Hallbjorner, H. Zirath, A. Alping, “High Gain Active Microstrip Antenna for 60-GHz WLAN/WPAN Applications,” IEEE Transactions on Microwave Theory and Techniques, vol. 54, issue. 6, pp. 2593- 2603, 2006. [10] A. Kaya, “High Gain Rectangular Broad Band Microstrip Antenna with Embeded Negative Capacitor and Chip Resistor,” Progress In Electromagnetics Research, PIER 78, pp.421–436,2008 [11] Siyang Sun, Yinghua Lu, Jinling Zhang and Fangming Ruan, “Genetic Algorithm Optimization of Broadband Microstrip Antenna,”Frontiers of Electrical and Electronic Engineering in China, volume 5, no. 2, pp.185-187. DOI: 10.1007/s11460-010-0015-0. [12] Debatosh Guha, Sudipta Chattopadhyay and Jawad. Y.Siddiqui, “Estimation of Gain Enhancement Replacing PTFE by Air Substrate in a Microstrip Patch Antenna,” IEEE Antennas and Propagation Magazine, vol. 52, no.3, june 2010.

[13]

Jui-Han Lu, Ren-Hao Chen, “ A Planar Inverted Ushaped Patch Antenna with High-Gain Operation for Wi-Fi/WiMAX,” Proc. of Asia Pacific Microwave Conference, 2009. [14] High Frequency Structure Simulator,Ansoft Corportion. [15] A. Dastranj, A. Imani, M. Naser-Moghaddasi, “Printed Wide-Slot Antenna for Wideband Applications,” IEEE Transactions on Antennas and Propagation, vol. 56, issue. 10, pp. 3097-3102, 2008 [16] B. K. Ang, B.K.Chuang, “A Wideband E shaped Microstrip Patch Antenna for 5-6 Ghz Wireless Communication,” Progress in Electromagnetics Research, vol .75, pp. 397-407, 2007.

A. Suman was born in Patna, Bihar, India on September 29, 1988. He is pursuing his B. Tech Degree in Electronics and Communication Engineering from Siliguri Institute of Technology, Siliguri under West Bengal University of Technology, West Bengal, India. He has already published some papers in international conferences. His area of interest includes RF, Microwaves, Wireless Communication and antenna engineering. R. K. Mistry was born in Siliguri, West Bengal, India on December 20, 1988. He is pursuing his B. Tech Degree in Electronics and Communication Engineering from Siliguri Institute of Technology, Siliguri under West Bengal University of Technology, West Bengal, India. He has already published some papers in international conferences. His area of interest includes Wireless Communication, Computer Networks and microstrip antenna. N. N. Dutta was born in Siliguri, West Bengal, India on October 05, 1989. He is pursuing his B. Tech Degree in Electronics and Communication Engineering from Siliguri Institute of Technology, Siliguri under West Bengal University of Technology, West Bengal, India. He has already published some papers in international conferences. His area of interest includes RF, Microwaves and antenna engineering. P. Chatterjee was born in Siliguri, West Bengal, India on March 07, 1989. She is pursuing her B. Tech Degree in Electronics and Communication Engineering from Siliguri Institute of Technology, Siliguri under West Bengal University of Technology, West Bengal, India. She has already published some papers in international conferences. Her area of interest includes electromagnetics and antenna engineering specially microstrip antenna. S. Chattopadhyay was born in West Bengal on September 10, 1974. He received his B.Sc (Physics Honours) from University of Calcutta in 1996 and B. Tech, M. Tech degree from Institute of Radio Physics and Electronics, University of Calcutta in 1999 and 2001 respectively. He is currently working as Assistant Professor of Siliguri Institute of Technology under West Bengal University of Technology, West Bengal, India. He is also pursuing for his Ph.D from The Universty of Calcutta. He is listed in Marquis Who’s Who

INTERNATIONAL JOURNAL OF ELECTRICAL, ELECTRONICS AND COMPUTER SYSTEMS (IJEECS), Volume 1, Issue 2, April 2011. ISSN: 2221-7258(Print) ISSN: 2221-7266 (Online) www.ijeecs.org

in the World, USA, 26th Ed, 2009 and also listed in 2000 Outstanding Intellectuals of The 21st Century, UK, 2010. He is a member of IEEE Antennas and Propagation Society. He has several publications in international journals and conferences. His area of research includes microwave antennas, microstrip and integrated antennas and computer aided design of patch antennas.

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Figure 1: Schematic diagram of proposed antenna (a) top view of patch, (b) side view of entire antenna structure.

Figure 2: Return loss profile of proposed antenna magnetic field distribution below the patch surface.

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E

H

Patch

L ~ λ/2

Figure 3: Electric field and magnetic field distribution below the patch surface. E Plane Pattern 0 330

10

30

0 -10 300

-20

60

-30 -40 -50 -60

270

90

-50 -40 -30 -20

240

120

-10 0 10

210

150 180

H Plane Pattern 0 330

10

30

0 -10

300

60

-20 -30 -40 270

90

-40 -30 -20 -10

240

120

0 10

210

150 180

Conventional Rectangular Patch Proposed U Type Patch

Figure 4: Radiation properties of the proposed antenna compared to conventional patch antenna : E plane and H plane.

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(a)

(b)

Figure 5: Electric field distribution over substrate of (a) proposed antenna structure (b) conventional patch antenna.