Design And Test Of Monocone Antenna For Global Spectrum Radio Telescope

The 21 cm signal detection is a key to study the early evolution of the universe and unravel the mysteries of the universe."The Hong Meng Project ultra-long-wave radio astronomical observation array will eventually be used to detect 21 cm global spectrum signals.In this paper,we design and test the monocone antenna of the radio telescope array unit for the ground verification experiment system in the project.Based on the analysis of the performance requirements of the global spectrum detection antenna,the selection design of the monocone antenna is proposed;the design of the electric geometric parameters of the monocone antenna is carried out;the simulation and optimization analysis of the electric geometric parameters of the antenna are carried out according to the technical indexes of return loss(-S11),3d B beam width and maximum radiation direction;after the electric geometric parameters are determined,the antenna structure design and prototype are carried out,and the performance of the monocone antenna is tested in the microwave anechoic chamber.The test results show that the antenna has smooth S11 in 30-120 MHz band,3d B beamwidth variation less than5 degrees,non-frequency variation of beam,etc,which can meet the project requirements.The ground effect analysis of antenna electrical performance was carried out for the ground effect problem in the ground verification experiment;according to the geographical condition of the ground experiment in Xinjiang Dahongliuxia,the testing scheme and testing work of soil conductivity by Wenner quadrupole method and soil dielectric constant by time domain reflection(TDR)method were proposed and carried out;from the soil test results,the electromagnetic simulation model of antenna soil effect was established,and the simulation analysis of the antenna electrical effect in the ground condition was carried out.The antenna electrical performance under ground conditions is simulated and analyzed;the impedance test of the antenna at ground site is carried out,and the maximum error of S11 between the measured and simulated results is 0.3d B;for the antenna loss problem of ground effect,the antenna electrical performance is tested in the field again after the ground screen is designed and produced,and the maximum error of S11 between the measured and simulated results is 0.8d B,which confirms that the ground screen design effectively improves the antenna electrical performance of ground effect.For the problem of difficult radio antenna beam measurement in the ground working environment,an antenna beam test system based on DJI M300 Pro UAV platform,consisting of signal transmitting,flight trajectory planning,signal receiving and other hardware and software,was designed and built;the antenna beam measurement experiments were carried out,and the experimental results showed that the test system could effectively test the antenna beam;the test results were found in the absence of ground network.The test results show that: the test system can effectively test the antenna beam;the test results are 5.64° difference between 3d B beam width and simulation under the condition without ground network,and 0.17 degree difference between maximum radiation direction;the difference between 3d B beam width and simulation under the condition of 32 ground networks is 11.95°,and 3.72 degree difference between maximum radiation direction,which further verifies the accuracy of antenna and ground screen design.The radio antenna design and simulation analysis,ground effect analysis and soil parameter measurement,the construction of antenna beam measurement system based on UAV platform,the microwave anechoic chamber test and ground work field test of the antenna prototype,etc.It lays a technical foundation for the engineering design of "Hongmeng Project" radio antenna,and is helpful to promote the development of 21 cm globel spectrum signal detection experiment.