Study Of Dual Frequency Co-plane Array And Circularly Polarized Yagi Antenna

In the process of rapid development of modern wireless communication,the antenna which is a very important components in communication system has been asked higher requirements,it includes the gain,polarization direction,beam width,axial ratio etc.Ordinary single antenna cannot meet these requirements,so people often use array antenna in the practical engineering application.In this paper,two kind of antenna have been researched and designed,both of them pass the test and meet the requirements of design index.The design content of the two kind of antenna is as follows:First of all,introduce basic theoretical knowledge about the two antennas.Include the classification of the microstrip antenna,the radiation mechanism,feeding method,the theory of linear array,the theory of planar array,the theory of feeding network and Taylor comprehensive distribution method.Then elaborate the Yagi antenna's working principle,basic structure and dimension design principle,the method for implementing circular polarization.Secondly,this paper expounds the design process of L\X band dual-frequency co-plane array antenna.High frequency array is nested into the low frequency array.Use the simulation software HFSS to simulate unit of dual band antenna,then analyze the main parameters,double unit coupling and double-frequency isolation.L band array is designed for 4 cells with array structure of 2×2,while X band array is designed for 144 cells with array structure of 12×12.Then this paper introduces the simulation of feeding network.feeding network of L band array designs as parallel feed with the structure ‘T' form and 4 output ports,while the line direction of X band array designs as cascade feed form with 12 output ports and Taylor distribution according to the design requirements of sidelobe,and column direction designs as parallel feed network with 12 output ports and Taylor distribution according to the design requirements of sidelobe.In order to achieve the Taylor distribution of the column direction of X band,simulate the six kind Wilkinson power splitters and combine into parallel feed network.According to the requirement of the deflection of the beam sweep with 30°,the X band column's output ports has phase difference with 112°.Simulate the whole structure of antenna,the gain of L band array is 11.6d Bi,while the gain of X band array with beam normal direction is 27.5d Bi.Throughthe design of the phase difference value,achieve the deflection of the beam sweep with ±30°,and the gains are 24.3d Bi and 25.4d Bi.Then test the antenna and analyze the test data and simulation data.Finally,this paper expounds the design process of circularly polarized Yagi antenna.Analyze the design index of the antenna,determine the total number of antenna's arm as 5.To ensure the design indicators of uplink frequency band 389-396 MHz,the center frequency has been moved to high frequency.Then simulate and optimize the antenna,ensure that the VSWR is less than 2.1 within the working frequency.Use phase shifter to produce a phase difference of 90° for antenna's feeder network,and make metal support between radial dipole and reflection dipole as a balun.Then test the antenna and analyze the test data and simulation data.The antenna gains at the center point of the uplink and downlink frequency are 8.8d Bi and 8.3d Bi,the axial ratio is less than 1.8 and the HPBW is more than 60° within the working frequency.The measured data is comparable to the simulation results.