Research And Design Of Antenna For S-Band Satellite Communication

Tiantong-1 satellite is an important part of China’s independently developed satellite mobile communication system.As China’s "maritime satellite",Tiantong satellite can cover China and the surrounding areas,the Middle East,Africa and other regions,as well as the Pacific Ocean,the Indian Ocean and other sea areas,which can provide stable communication services for marine rescue,air transport and personal mobile communication.This article is based on the research background of Tiantong-1 satellite working in the S-band.In this paper,three types of circularly polarised antennas with different structures are designed and analysed for different scenarios,and the low elevation angle,wide beam and miniaturisation characteristics of the antennas are investigated.The three different forms of S-band circularly polarised antennas are as follows:The first type is a laminated gap-coupled anti-metal microstrip antenna.A modified form of the traditional microstrip antenna,the gap-coupled microstrip antenna,is used to separate the feed network and the radiating patch to reduce the interference between the two.Two output ports with equal amplitude and phase difference of 90 degrees are realised by Wilkinson network,and the feed network is fed against a floor with a gap to realize left-hand circular polarisation.The conventional rectangular slit is improved to an H-shaped slit,allowing the antenna to obtain more coupling to increase the beamwidth.Introduction of a metal reflector to improve the backward radiation overload of the slit antenna.A metallic aluminium cavity is introduced to improve the antenna’s metal resistance and impedance matching performance.Finally,result shows that VSWR is less than 1.2,center gain is greater than 6d Bi,the antenna emits stable radition above ±30° elevation angle and 3d B beamwidth is greater than 110°.The second type is a wide beam crossed magneto-electric dipole antenna.Because the electric dipole and magnetic dipole have complementary characteristics,and by combining the two radiation direction diagrams,a wide-beam magneto-electric dipole antenna with good radiation in the upper hemisphere is designed.The electric dipole is an aluminium radiating element with a bevelled structure and the magnetic dipole is an inclined cylinder with a stepped structure,and a pair of magnetoelectric dipoles are placed crosswise to achieve omnidirectional radiation in one cycle.A Wilkinson power divider is used to feed the crossed magneto-electric dipoles to achieve circular polarisation,and a metallic aluminium cavity is introduced to enhance the overall gain and impedance matching performance of the antenna.Finally,result shows that VSWR is less than 1.2,center gain is greater than 5.5d Bi,the antenna emits stable radition above ±30° elevation angle and 3d B beamwidth is greater than 120°.The third type is the miniaturized four-arm spiral antenna.Four identical radiating arms with a90° difference in rotational pitch are etched onto a flexible dielectric plate to form a prototype of a four-armed spiral antenna.The four output ports with equal amplitude and 90° phase difference are fed to the radiating arms through a one-point four Wilkinson network to realize left-handed circular polarisation.The height of prototype antenna is 60 mm,which is reduced to 55 mm by introducing parasitic radiating arms to widen the antenna bandwidth.By curving the radiating arms,the height is reduced to 36 mm.Finally,result shows that VSWR is less than 1.5,center gain is greater than 5d Bi,the antenna emits stable radition above ±30° elevation angle and 3d B beamwidth is greater than 140°.