The Study Of UHF Dual Polarized Microstrip Antenna

As an indispensable part of wireless communication system,antenna plays a vital role in the performance of the system.With the development of science and technology,the requirements for the performance of the antenna are getting higher and higher.Dual polarized antenna uses two polarized orthogonal signals within the same frequency band,the interference between each other is so small that the frequency band can be used effectively,which is especially important for the era of increasingly tense frequency band resources.Microstrip antenna has the advantages of small volume,light weight,low profile,conformal easily and so on,and it has been widely used in wireless communication system.In this paper,a dual-polarized microstrip antenna of aperture coupled feeding is studied,Because aperture coupled feeding has merits of the small influence of feeding system on radiation element,easily realizable impedance matching and low cross-polarization.Firstly in this paper,the basic theory and analyzing method of microstrip antenna are described,including transmission line model theory,cavity model theory and integral equation method.Then several common feeding modes of microstrip antenna are introduced,including microstrip line,coaxial line,electromagnetic coupling and aperture coupling,and also analyze and compare their advantages and disadvantages.Finally a dual polarized microstrip array antenna and a dual circular-polarized microstrip antenna array are investigated respectively.According to the technical indicators of UHF band dual polarized microstrip antenna,a ±45° dual polarized microstrip antenna unit is designed with a center frequency of 642 MHz,modeled and simulated by Ansoft HFSS software.Because the gain of a single antenna is only 8.3d B,a 2-element dual polarized microstrip array antenna is designed with this antenna element.An important part of the array is to design the corresponding feeding network which is built on the basis of the Wilkinson Power Divider theory.The performance parameter of the antenna is got by simulation and optimization with the VSWR of the proposed antenna being less than 1.5,the isolation between two ports of the proposed antenna is 31 d B,the maximum achievable gain of the proposed antenna is 11 d B,the cross polarization level exceeding 21 d B,and the front-to-back ratio being larger than 17 d B within the working frequency band(606~678MHz).According to the technical indicators of UHF band dual circular-polarized microstrip antenna,a dual circular-polarized microstrip antenna element with a center frequency of 435 MHz is designed.The cell structure is identical to the former dual polarized antenna,the feed lines are placed orthogonally so as to form the horizontal and vertical dual polarization,besides,it generates 90° phase difference to form circular polarization,and the HFSS software is exerted to model and simulate.Because the gain of the antenna cell is only 8.8d B,a 2×2-element dual circular-polarized microstrip array antenna is designed with this antenna element.An important part of the array antenna is to design the corresponding feeding network.A branch-line coupler is designed in the feeding end to connect the two networks together so as to ensure that the network ends can form a 90° phase difference.The performance parameter of the proposed antenna is got by simulation and optimization with the VSWR of the antenna and the axial ratio being less than 1.5 and 1.5d B respectively,the isolation between two ports of the proposed antenna is 36 d B,the gain and the front-to-back ratio being larger than 12 d B and 17 d B respectively within the working frequency band(430~440MHz).