Design And Simulation Of VHF Band Dipole Antenna

This paper introduced the design and optimization of VHF(very high frequency)band antenna and ground screen,finally the performance of the antenna system satisfied the requirements of low-frequency radio observation.The main work is:Firstly,based on the characteristics of the low-frequency radio observation and the observation system model,the Galaxy background noise and the back-end receiver noise temperature were studied,and we calculated the technical specifications of the antenna.According to the principle of the half-wave dipoles and the method of broadening working frequency,we used the electromagnetic simulation software design the blade-type half-wave dipoles.The bandwidth was increased by increasing the width of the antenna panel,and the impedance matching was improved by changing the shape of the feeding part.Finally,the antenna arm length is 1.8m,the arm width is 0.4m,the feeding part is an isosceles triangle,and the apex angle is 90 degrees.Then we simulated the radiation characteristics of the dipoles on four different grounds.Without ground screen,the gain of antenna on the dry grounds are 3.06 dB and 1.435 dB,on the moist grounds are 4.327 dB and 4.246 dB.After placing the ground screen,the gain of the antenna on the dry grounds are 4.869 dB and 4.971 dB,on the moist grounds are 4.286 dB and 4.403 dB.The ground screen can not only stabilize the performance of antenna,but also effectively improve the radiation characteristics of the antenna.Finally,according to the simulation results,we made the blade-type dipoles and the stainless steel ground screen with aluminum plate,and tested dipoles in combination with the hollow balun.The test results show that the first resonant frequency of the dipoles was 25.9MHz,and the second resonant frequency was 79.4MHz.Although there are some deviations from the simulation results,the voltage standing wave ratio of the dipoles in the working frequency band is lower than the simulation result,and the impedance matching completely satisfies the low frequency.radio observation requirements.