Design And Experimental Study Of Measurement Antenna For The Cosmic 21cm Global Spectrum

In order to study the early evolution history of the universe,the astronomical Honngmeng Project is being carried out in China to detect the 21 cm global spectrum.According to the requirements of global spectrum system,the antenna design and experimental research are carried out in this paper.The requirements of global spectrum system,signal frequency band and frequency independent antenna are analyzed.The antenna selection design of the project-matched and non-matched measurement systems is carried out.The non-matched system uses a cone monopole antenna,and the matched system uses a plane dipole antenna.The first phase of the project is a ground verification system.The design of radial grounding network was carried out.Some key problems of this method like frequency independent antenna,broadband matching,ground effect reduction,antenna measurement site selection are studied.For non-matched measurement system,the antenna characteristic impedance theory and empirical formula are applied to determine the electrical geometric parameters of the discone monopole antenna.The electromagnetic models of infinite and finite discone monopole antennas are established.Electromagnetic simulation,broadband matching,electric small antenna,loading technology,and single factor method are applied to simulate and analyze antenna.According to the results of antenna return loss(S11 parameter),the electrical performance of antenna,which influenced by ground reflection,is studied.The electrical geometric parameters of the antenna are optimized.In the band between 50 and 200 MHz,the maximum S11 parameter is-0.625 d B,and resonant frequency is 233.022 MHz.The return loss curve is smooth.The beam of antenna achieves frequency independent design.According to the design results of electrical geometric parameters,the antenna structure design of the antenna cone radiator and dielectric support body was carried out.The antenna prototype is made and tested in Beijing.Within 50?200MHz,S11<-1.5d B,resonant frequency is about 235 MHz.The test results of Xinjiang radio observation station with excellent electromagnetic environment are: within 50?200 MHz,S11<-2d B,resonant frequency is about 234 MHz.In two places,the antenna beam patterns are tested and achieved frequency independent antenna design.For matched measurement system,the antenna characteristic impedance theory and empirical formula are applied to determine the electrical geometric parameters of the plane dipole antenna.The electromagnetic models of finite plane dipole antenna is established.Electromagnetic simulation,broadband matching,and single factor method are applied to simulate and analyze antenna.The electrical geometric parameters of the antenna are optimized.In the band between 52 and 105 MHz,S11 <-10 d B.The return loss curve is smooth.And the beam of antenna achieves frequency independent design.According to the results of the electro geometric parameters design,the antenna feed structure,balun structure,radiator support structure,ground frame and other structures are designed.The antenna prototype is made and tested in Beijing.Within 50?105 MHz,S11<-10 d B.The antenna achieves the design of frequency independent and broadband matching.In this paper,discone monopole antenna can meet requirements of the project's mismatching measurement system,and plane dipole antenna can meet requirements of the matching measurement system.These two kinds of antennas promote the smooth implementation of the Hongmeng Project in astronomy in China,and lay the foundation of Engineering antenna technology.