The document reviews various methods for enhancing the bandwidth of microstrip patch antennas. It discusses how modifying the patch shape, using multilayer configurations, planar/stacked multi-resonator structures, and different feeding techniques can increase the antenna's bandwidth. Modified patch shapes, multilayer structures, and proximity coupled feeding provide the greatest bandwidth enhancements, with multilayer designs potentially achieving over 70% bandwidth. The review concludes that slot loading and multilayer techniques are most effective for enhancing bandwidth while maintaining a small antenna size.

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(An Association Unifying the Sciences, Engineering, and Applied Research)
International Journal of Emerging Technologies in Computational
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IJETCAS 14- 615; © 2014, IJETCAS All Rights Reserved Page 276
ISSN (Print): 2279-0047
ISSN (Online): 2279-0055
A Review on Bandwidth Enhancement Methods of Microstrip Patch Antenna
Tanvir Singh Buttar1, Narinder Sharma2
1 M.Tech. Scholar, Department of ECE, AICTE, PTU, Amritsar College of Engg. & Tech., Amritsar- Jalandhar GT road, Manawala, Amritsar, India, tanvirbuttar88@gmail.com
2 Associate Professor, Department of EEE, AICTE, PTU, Amritsar College of Engg. & Tech., Amritsar- Jalandhar GT road, Manawala, Amritsar, India, narinder.acet@gmail.com
Abstract: Microstrip patch antenna (MPA) plays significant role in modern communication devices. And a large part of daily communication is done by using MPA. The study of MPA has made great progress in recent years. The study of literature work shows that the major work is concentrated on designing small sized broadband MPA. As the antennas are build smaller, the operating bandwidth decreases. Hence to improve bandwidth different techniques are used. This review paper delivers various bandwidth enhancement techniques since last few years.
Keywords: Microstrip patch antenna (MPA), Bandwidth enhancement, Dielectric constant, Antenna design, substrate.
I. Introduction
Physically, MPA is made up of dielectric substrate which is sandwiched between a radiating flat rectangular sheet or patch of metal and a larger sheet of metal called ground plane. The radiating patch is made up of conducting material like gold or copper and can have any shape. The feed lines and radiating materials are photo etched on the dielectric substrate as shown in figure 1.
Fig. 1. Microstrip Antenna configuration
The height (h) of the dielectric substrate usually ranges from 0.003 λo ≤ h ≤0.05 λo, where λo is the free space wavelength and the dielectric constant of the substrate (εr) ranges from 2.19 to 12. The MPA becomes popular in the world of wireless communication system because of its low profile, easy and low cost fabrication, light weight non-planar and planar geometries easy integration of components, mechanical robustness, easy association in arrays.
II. Excitation Techniques
The MPA can be excited by different methods. These feeding techniques are majorly classified into two categories: contacting and non-contacting feed technique. In contacting feeding technique the power is fed directly to the radiating patch by using a connecting element such as microstrip line. In non-contacting feed technique an electromagnetic field coupling is done to transfer power between radiating patch and microstrip line. The four most common feed techniques are microstrip line and coaxial probe (both contacting techniques); aperture coupling and proximity coupling (both non-contacting techniques).
III. Methods of Analysis of Microstrip Patch Antenna
The analysis mechanism for MPA are divided into two parts. First part is based on equivalent magnetic current distribution around the patch edges. There are three analytical techniques:The transmission line model,The cavity model, The full-wave model. The second part is based on the electric current distribution on patch conductor and the ground plane. The numerical methods are as:The finite element method (FEM), The spectral domain technique (SDT), The method of moments (MOM), The finite difference time domain (FDTD) method.
The analytical methods are less accurate, gives good physical insight and require less computation where as the numerical methods are more accurate, gives less physical insight and requires more computation.

2. Tanvir S. Buttar et al., International Journal of Emerging Technologies in Computational and Applied Sciences, 9(3), June-August, 2014,
pp. 276-279
IJETCAS 14- 615; © 2014, IJETCAS All Rights Reserved Page 277
IV. Need of Higher Bandwidth
Generally, the MPA has a narrow bandwidth besides that today wireless communication system demands higher operating bandwidth. These communication devices need higher bandwidth so as to work in the broader band in order to shoulder high speed internet, multimedia communication like 9.5% for a digital communication system (1710-1880 MHz), 12% for universal mobile telecommunication system (1920-2170 MHz), 7% for global system for mobile communication (890-960)[1]. In order to fulfil the demands of the bandwidth various techniques are employed and some of them are described in this review paper.
V. Literature Survey
The concept of MPA revert back about 26 years to work by Deschamps in USA[2], by Gutton and Baissinot in France[3]. Afterwards Lewin explored radiation from stripline discontinuities. Further studies were assumed in 1960 by kaloi, who considered the rectangular and square configurations. But the report of Deschamps work was not announced until the 1970’s, when the conducting strip radiator ( half wavelength wide and a few wavelengths long fed by coaxial connections) separated by a dielectric substrate from a ground plane was explained by Byron. This concept was used in Project Camel. After that, the microstrip element was manifested by Munson[4] and data on circular and rectangular microstrip patched was reported by Howell. Weinschel evolved various microstrip geometries for use with cylindrical S band arrays on rockets. Further work on basic microstrip patch elements was announced in 1975 by Garvin et al, Weinschel, Janes, Howell and Wilson. The development of microstrip antennas by Munson, for use as low profile flush mounted antennas on missiles and rockets reveals that this was a practical concept which can be used in solving various antenna problems and hence invented the new antenna industry.
Parminder singh et. al [5], highlighted the bandwidth enhancement of probe fed MPA. Chen and Zhang [6] explained the bandwidth enhancement of a microstrip of a microstrip-linefed printed wide slot antenna with a fractal shaped slot. Shubam Gupta et al[7], described the bandwidth enhancement in multi patch microstrip antenna array. M. Gujral et al[8], introduces the bandwidth improvement of microstrip antenna array using dummy EBG pattern on feed line. Song and Zhang [9], desigend a novel momopole antenna with a self similar slot for wideband applications. R.C Hadarig M.E. de Cos and F. Las-Heras [10], have presented microstrip patch antenna with enhanced bandwidth using AMC/EBG structures. Sandeep Kumar et. Al[11], proposed a design of microstrip square shaped patch antenna for improvement of bandwidth and directivity gain. Parmar, and Makwana [12], introduces the bandwidth enhancement of microstrip patch antenna using parasitic patch configuration. Jia-Yi Sze and Kin-Lu Wong [13], shows the slotted rectangular microstrip antenna for bandwidth enhancement. Qu, D. ; Shafai, L. ; Foroozesh, A. [14], highlights the Improvement of microstrip patch antenna performance using EBG substrates. D. C. Chang, J. X. Zheng [15], describes the Wide-Band microstrip antenna using two triangular patches. Parminder singh, Anjali Chandel, Divya Naina[16], explains the bandwidth enhancement of probe fed microstrip patch antenna. Juhua Liu, Quan Xue, HangWong, Hau Wah Lai, and Yunliang Long [17], describes thedesign and analysis of a low- profile and broadband microstrip monopolar patch antenna. Y. Sung [18], introduces the bandwidth enhancement of a microstrip line-fed printed wide-slot antenna with a parasitic center patch. Aliakbar Dastranj and Habibollah Abiri [19], highlights the bandwidth enhancement of printed e-shaped slot antennas fed by cpw and microstrip line.
VI. Techniques To Enhance Bandwidth Of Microstrip Patch Antenna
The techniques used to uplift the bandwidth of the microstrip patch antenna are described below.
A. Broadband Mcrostrip Patch Antennas Having Modified Patch Shapes
Bandwidth is enhanced by using this technique by simply modifying i.e changing the radiating patch’s shape. In other words by changing the shape of rectangular and circular patches into rectangular ring and circular ring so as to enhance the Bandwidth. By modifying the shapes of the patches the bandwidth improves because the quality factor reduces, as the less energy will be stored under the patch and produces higher radiation.
B. Broadband Mcrostrip Patch Antennas Having Multilayer Configuration
The patches are planted over the various dielectric substrates and are stacked on each other, in case of multilayer configuration. The coupling in the multilayer configuration can be done in two ways either by electromagnetic coupling or aperture coupling.. Ground plane have an aperture slot in aperture coupling and to avoid the radiation losses the substrate is made up of high dielectric constant and the top patch is made up of thick dielectric substrate with low dielectric constant. In electromagnetic coupled MPA one or more patches are placed over different dielectric layers. In two layered configuration then any one of them is fed and other is electromagnetically coupled.

3. Tanvir S. Buttar et al., International Journal of Emerging Technologies in Computational and Applied Sciences, 9(3), June-August, 2014,
pp. 276-279
IJETCAS 14- 615; © 2014, IJETCAS All Rights Reserved Page 278
Although the dielectric constant and dimension of the patch may varies but the resonant frequency is near to each other in order to have high bandwidth [20]. Broad bandwidth approximately 70% can be obtained by making use of multilayer configuration.
C. Broadband Microstrip Patch Antenna Having Planar Multiresonator Configuration
In the planar multi-resonator configuration the multiple resonators are placed close to each other and only one is fed and others are parasitically coupled also called as gap coupled. This configuration can also be fed by directly connecting the patches through microstrip line. In certain cases both direct and gap coupling is used and is called as hybrid coupling. The major disadvantages of this configuration is that these configuration is not suitable for an array configuration, as their size is too large and there is changes in the radiation pattern over the impedance matching.
D. Broadband Microstrip Patch Antenna Having Stacked Multiresonator Configuration
This configuration is evolved by the combination of stacked configuration and multi-resonator configuration in order to further enhance the bandwidth. Although the size of the stacked multi-resonator microstrp patch antenna is not small but it provides very high bandwidth and gain.
Table1: Comparison of different broadband techniques
S. No.
Broadband Techniques
Configuration
Remarks
1.
Modified patch shapes
T-slot rectangular patch[21]
Impedance Bandwidth of 25.23% with average gain of 7.43 dBi is obtained.
E-H shaped patch[22]
Delivered bandwidth is about 27%
U-shaped slot with single-layer single- patch[23]
Air substrate of 12 mm is used to provide bandwidth of 27.5%.
2.
Multilayered Technique
Multilayered configuration of patches[24]
Nearly 70% of bandwidth can be otained by making use of multilayered configuration of radiating patches
3.
Multi resonator Technique
Gap-coupled multi resonator and stacked configuration[25]
delivers bandwidth of 25.7% with more than 10 dB gain.
Shifted parasitically coupled multiresonator[26]
Improves the impedance bandwidth from 65 MHz to 251 MHz
Directly coupled and parasitic patches[27]
Impedance bandwidth of 12.7% (365 MHz) is yeilded, which is 6.35 times when compared with the simple patch i.e. 2% (54 MHz) at same center frequency of 2879 MHz
4.
Stacked Multilayered Technique
Gap-coupled planar multiresonator and stacked configuration[25]
bandwidth of 25.7% with more than 10 dB gain
Stacked U-slot microstrip antenna incorporating E-shape and modified half-E shape radiating patch configuration[28]
Maximum impedance bandwidth of 60.2% can be obtained
E. Impact of Varrious Feeding Techniques on Bandwidth of Microstrip Patch Antenna.
There are variety of feeding techniques which can be used to feed the microstrip patch antenna. Feeding techniques are broadly categorised into two categories: contact feeding and non-contact feeding. These techniques are mentioned above in this paper. A better impedance matching between a patch and the feed line without using any extra matching element depends on the type of feeding technique used. As shown in table the proximity coupled feed technique provides the highest bandwidth.
Table 2: Comparison of Feeding Techniques
Characteristics
Microstrip Line Feed
Coaxial Feed
Aperture Coupled Feed
Proximity Coupled Feed
Bandwidth
2-5%
2-5%
2-5%
13%
VII. CONCLUSION
Low bandwidth is always the limitation of MPA. The impact of different broadband microstrip patch antenna configurations and feeding techniques on the bandwidth of the microstrip patch antenna has been presented in this paper so as to increase the operating bandwidth. After an exhaustive study of literature work it is perceived that in case of feeding techniques, the proximity coupled feeding technique delivers the maximal bandwidth. And among all techniques multilayer structures provide maximum bandwidth but its size increases with the increase in number of layers. Slot loaded techniques can be used to further enhance the bandwidth as they have inherent advantage that the size of the antenna remains small.

4. Tanvir S. Buttar et al., International Journal of Emerging Technologies in Computational and Applied Sciences, 9(3), June-August, 2014,
pp. 276-279
IJETCAS 14- 615; © 2014, IJETCAS All Rights Reserved Page 279
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