The Study Of L/S Band Dual Polarized Antennas And Arrays

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.Based on the application of dual polarized base station antenna,the dual polarized microstrip antenna is studied in the form of electromagnetic coupling feed.Firstly in this paper,the basic theory and analyzing method of microstrip antenna are described,including its structural characteristics,analysis method and electrical parameters.Then several common feeding modes of microstrip antenna are introduced,and analyzed and then compare their advantages and disadvantages.Secondly,three kinds of dual polarization antennas are designed,including broadband dual line polarized microstrip array antenna,broadband dual circularly polarized microstrip array antenna,and broadband dual circularly polarizing patch antenna.The specific contents are as follows.According to the requirement of L/S band dual line polarization base station antenna,a 1 x 2 broadband dual line polarized microstrip array antenna is designed.The center frequency is 2.35 GHz,and the modeling and simulation calculation are carried out by using Ansoft HFSS software.The antenna adopts the form of electromagnetic coupling feed,which can easily match the broadband impedance.At the same time,the structure of differential feed is used to reduce the cross polarization of the antenna,and the horizontal and vertical polarization is realized.An important part of the array is to design the corresponding feeding network which is built on the basis of the Parallel double line to microstrip line theory.The performance parameter of the antenna is got by simulation and optimization with the VSWR of the proposed antenna being less than 2,the isolation between two ports of the proposed antenna is 27 dB,the maximum achievable gain of the proposed antenna is 11 dB,the cross polarization level exceeding 21 dB,and the front-to-back ratio being larger than 17 dB within the working frequency band(1.82~2.87GHz).Then,adding a 90 degree phase shifter to the feed network of a dual line polarized antenna array,the original differential feed structure is transformed into a four point feed,which makes the antenna array double circularly polarization.Through simulation and optimization,the parameters of the broadband dual circularly polarized microstrip array antenna are obtained,and in the working frequency band(1.85~2.73GHz).The VSWR is less than 2,the polarization port isolation is above 24 dB,the gain is greater than 11 dB,and the degree of cross polarization isolation is greater than 22 dB.Finally,a broadband dual circularly polarizing patch antenna with the central frequency of 2.35 GHz is designed.The broadband impedance bandwidth is realized by the inverted L probe feed.The broadband phase shifter is designed to ensure the 90 degree phase difference of the network in a wide frequency band,and the wide axial ratio bandwidth is achieved.Through simulation and optimization,the performance parameters of the antenna are obtained.In the working frequency band(1.73~2.73GHz),the VSWR is less than 2,the axial ratio is less than 3dB,and the gain is more than 6dB.