Increase Bandwidth for Circular Microstrip Patch Antenna

Transcription

1 ISSN Volume, Issue 1 Increase Bandwidth for Circular Microstrip Patch Antenna Sonali Jain, Rajesh Nema Abstract In this paper a design and performance of a circularly microstrip patch antenna, for the application in Wireless Local Area Network (WLAN), are reported here. The antenna is a proximity coupled microstrip patch antenna where the radiating patch is loadedby a V-slot. This miniaturized microstrip antenna has wide bandwidth in the frequency band of WLAN and exhibits circularly far field with very good axial ratio bandwidth. The simulated results using IE3D software are verified by measurement. I. INTRODUCTION This article introduces some of the basic concepts of patch antennas. The main focus will be on explaining the general properties of patch antennas by using the simple rectangular probefed patch. It will cover topics including: principles of operation, impedance matching, radiationpattern and related aspects, bandwidth, and efficiency.microstrip antennas have profound applications especially in the field of medical, military, mobile and satellite communications. Their utilization has become diverse because of their small size and light weight. Rapid and cost effective fabrication is especially important when it comes to the prototyping of antennas for their performance evaluation. As wireless applications require more and more bandwidth, the demand for wideband antennas operating at higher frequencies becomes inevitable. Inherently microstrip antennas have narrow bandwidth and low efficiency and their performance greatly depends on the substrate parameters i.e. its dielectric constant, uniformity and loss tangent. Microstrip patch antennas are attractive for their well-known efficient features such as compatibility with monolithic microwave integrated circuits (MMIC), light weight, less fragile, low profile etc. The main disadvantage associated with microstrip patch antennas is the narrow bandwidth, which is due to the resonant characteristics of the patch structure. But on the other hand modern communication systems, such as those for wireless local area networks (WLAN), as well as emerging applications such as satellite links (vehicular, GPS,etc.) often require antennas with low cost and compactness, thus requiring planar technology. Due to the light weight of the microstrip patch antennas, they are appropriate for the systems to be mounted on the airborne platforms such as synthetic aperture radars (SAR) and scatterometers. Because of these applications of the microstrip patch antenna, a new motivation is evolved for research and development on indigenous solutions that overcome the bandwidth limitations of the patch antennas. In applications in which bandwidth enhancement is required for the operation of two separate subbands, an appropriate alternative to the broadening of the total bandwidth is represented by dual-frequency microstrip antenna, which exhibits a dual-resonant behavior in a single radiating element. The radius of the antenna is 100 mm. II. ANTENNA STRUCTURE AND RESULTS Antenna element structure is shown in Fig.1. Using the form of cutting H Shape of Circular microstrip patch antenna. This antenna design a multi layer used, first layer a glass epoxy and nd layer duroid layer.the antenna fabricated on an h=1.5mm glass eproxy substrate with the dielectric constant ξr =4.3 and loss tangent tanδ=.019.and other layer used of antenna fabricated an h=.508mm duroide epoxy substrate with the dielectric constant ξr=.33 and loss tangent tanδ= Simulated and measured curves of Return loss (db) vs Frequency of antenna shown in fig. III. ANALYSIS OF CIRCULAR PATCH MICROSTRIP ANTENNA. 1. Equivalent dielectric r1 r( h1 h ) eq h ( h h ) r1 r 1 1. Circular Patch Radius and Effective Radius K a f a e nm C eq h a a{1 [ln( ) 1.776]} a h eq 1 169

2 ISSN Volume, Issue 1 Fig1. Geometry of Circular Microstrip Patch Antenna 170

3 ISSN Volume, Issue 1 Conductance The conductance due to the radiated power of the circular microstrip patch antenna can be computed based on the the radiated power expressed as; V0 ( K0ae ) Prad [ J ' 0 cos J0]sind K 0 is the free space phase constant. The conductance across the gap between the patch and the ground plane at φ =0o is given as ( Ka 0 e) Grad {[1 sin sin sin ] [1 sin sin sin ]} Grad accounts for radiation and dielectric losses and are expressed as 3 3 c m0 0 r 10 0 e G ( ( f ) ) [( K a ) ] G d tan 4 ( ) m0 [( Kae) ] 0h fr 10 as where G c is the conductance due to conduction losses, G d is the conductance due to dielectric losses and f r is the resonant frequency of the dominant mode. The total conductance can be expressed Gt Grad Gc Gd 4.Directivity D 0 ( Ka 0 e) 10G rad This directivity is not strongly influenced by height of substrate as long as it is maintained electrically small. It is a function of patch radius. III. RESONANT INPUT IMPEDANCE The input impedance of a circular patch at resonance is real and the input power is independent of the feed point position on the circumference (Balanis, 198). Taking the reference of the feed point at, the input resistance at any radial distance from the center of the patch can be written as (Balanis, 198) J ( K ) Rin G J Ka 1 [ m 0 ] t m( e) For the circular patch antenna, the resonant input resistance with an inset feed is m in( ' 0) in( ' e) Jm R R a J ( K0) ( Ka ) PROGRAM DESIGN AND SIMULATION The program written in FORTRAN using WATFORT g77 compiler was developed based on equations (17) to (35). The program was run on the DOS mode and results exported to Microsoft word.the main program reads in the microstrip parameters then determines the ideal radiation characteristics Input Parameters ξ eq = dielectric constant h= height of substrate C = Speed due to free space Output Parameters a = radius of patch a e = effective radius of patch G rad = Conductance between gap & ground G d = conductance due to dielectric G t = total conductance D 0 = directivity of slot R in = resonant of input resistance The calculate parameters for different antennas designed at various feeding point at a 5Ghz frequency are given in table:- Circular microstrip patch antenna results in table S.NO Co-Ordinates Result in db Bandwidth Directivity 1-170,-9-1db 7.6% 9.33db -1, db 1% 6.88db 3-301, db 1% 7.76db 4 9,- -db 8% 5.95db 5-140, db 1% 9.57db 6-68,-33-14db % 7.34db 7-81,-38-14db 3% 6.71db 8 95,0-30db 34% 8.33db e 171

4 ISSN Volume, Issue 1 IV. RESULTS The simulated results of the antenna comprise of return loss(db).fabricated antenna at frequency 5GHz. simulated Frequency GHz Fig.-GHz Antenna Results Fig3.-Simulated VSWR vs.frequency of antenna 17

5 ISSN Volume, Issue 1 V. CONCLUSION This study provided an insight in determining the performance of microstrip patch antenna. From the results presented it is observed that glass epoxy and duroid epoxy for X-band antenna designs. However,first theoretically calculated parametric dimensions and simulated results should be properly analyzed. Then based on the analysis,predesign calibrating corrections may be incorporated in the bandwidth development process.predesign bandwidth are maximum 15% and this paper of bandwidth 34%.It means 19%bandwidth improvement this paper. ACKNOWLEDGEMENTS The authors, for this work, deeply acknowledge the professional guidance provided by Mr. Rajesh Nema, and financial support by NIIST. The authors also sincerely recognize technical help and day to day supported. REFERENCES [1]. Al-Zoubi, F. Yang, and A. Kishk, A broadband center-fed circular patch-ring antenna with a monopole like radiation pattern, IEEE Trans. Antennas Propag., vol. 57, pp , 009. []. M. John and M. J. Ammann, Wideband printed monopole design using a genetic algorithm, IEEE Antennas Wireless Propag. Lett. vol.6, pp , 007. [3]. S. K. Oh, H. S. Yoon, and S. O. Park, A PIFA-type varactor-tunable slim antenna with a PIL patch feed for multiband applications, IEEE Antennas Wireless Propag. Lett., vol. 6, pp , 007. [4]. C. H. Chang and K. L. Wong, Printed -PIFA for penta-band WWAN operation in the mobile phone, IEEE Trans. Antennas Propag., vol. 57, pp , 009. [5]. Nasimuddin and Z. N. Chen, Wideband multilayered microstrip antennas fed by coplanar waveguide-loop with and without via combinations, IET Microw. Antennas Propag., vol. 3, pp , 009. [6]. W. C. Liu, Design of a multiband CPW-fed monopole antenna using a particle swarm optimization approach, IEEE Trans. Antennas Propag., vol. 53, pp ,