| With the rapid development of China’s satellite communication industry in recent years,tiantong-1 01 satellite was successfully launched in 2016,tiantong-1 02 satellite was successfully put into the predetermined orbit in 2018,and tiantong-1 03 satellite was successfully launched in2021.Since then,it has opened the door for the development of China’s military and civil autonomous satellite mobile communication services.Tiantong-1 satellite is different from the L-band used by INMARSAT.The satellite works in the S-band,specifically from 1.98 Ghz to2.2GHz.It has obvious advantages in the number and bandwidth of transponders.Therefore,as the matcher of circuit and free space,S-band antenna plays a vital role in the receiving and transmitting process of satellites in this band.Tiantong-1 satellite mainly adopts circular polarization radiation,which is different from the simple linear polarization radiation in the past.Circular polarization antenna has great advantages in target tracking,satellite positioning and other fields.In particular,when the antenna is in high latitude or carried on UAV and other equipment,the included angle between tiantong-1 satellite and the normal of the antenna is very large,often in the range of nearly60 °,which requires a very large receiving angle range of the antenna,and within this angle range,the antenna must maintain a certain radiation intensity gain.Therefore,under the project background of antenna 1 satellite communication circular polarization antenna,this dissertation selects a variety of standing wave and traveling wave antennas for design,and studies and designs the problems of low elevation,wide beam and miniaturization of most antennas in this frequency band.This dissertation mainly designs three kinds of circularly polarized antennas with different structures:The first is a three-layer dual circularly polarized slot coupled microstrip antenna loaded with I-shaped slots.The slot coupling antenna is selected in the microstrip antenna structure to reduce the radiation interference of the feed network.In order to realize left and right circular polarization respectively,the feed network of the antenna adopts a directional coupler structure with dual port feed.Two circularly polarized waves with different phase difference but the same amplitude can be realized by inputting signal excitation at the two ports respectively,so as to realize left-handed circular polarization and right-handed circular polarization.In order to increase the beam width,the traditional I-shaped slot is changed to I-shaped slot to obtain more coupling.In order to solve the back radiation brought by the slot and reduce the out of roundness of the pattern,a third layer of metal reflector is added to the two-layer structure of the traditional slot antenna.The simulation results show that the antenna can emit high-gain electromagnetic radiation in the beam range of120°,the 120° Angle gain is greater than 1d Bi in both upper and lower frequency bands,and the center gain of 0° can be up to 6.7d Bi in the case of dextral circular polarization.The VSWR of both ports is less than 1.4 in the operating band 1.98 Ghz to 2.2Ghz,and the Axial Ratio is less than 3d B in the 100° beamwidth.At the same time,based on the single array antenna,a four-array antenna with higher gain is designed.The test results show that the VSWR in the working band is less than1.8,and the maximum gain in the center is more than 10 d Bi.The second is a self phase shifted cross dipole antenna.Based on the principle of complementary pattern of electric oscillator and magnetic oscillator,the two structures are combined to improve the low elevation gain and pattern roundness of the antenna.Two identical electric oscillators are placed orthogonally to form a cross oscillator structure,and a quarter wavelength metal ring is added between adjacent oscillators to make the antenna produce a-90°phase shift and realize the circular polarization characteristics.Eventually antenna has a radius of only 38 mm and a height of only 18 mm,which can maintain a high gain within the beam range of120°.The minimum gain at the 120° Angle is 1.4d Bi,and the maximum gain at the center is 5.6d Bi.Meanwhile,the VSWR of the port is less than 1.4 in the range of its frequency band,and the 3d B Axial Ratio beamwidth is greater than 90° at the upstream and downstream center frequencies.The third is a miniaturized circularly polarized four arm helical antenna.Four arm helical antenna can be regarded as an antenna array composed of four identical helical arms.Each antenna arm is fed by power divider or bridge,and the voltage amplitude at the port of each antenna arm is equal,and the phase difference is-90° according to the requirements of left-handed circular polarization.The height dimension of traditional spiral arm antenna is often one quarter of the working wavelength of integral multiple.Taking the working frequency band of this design as an example,the antenna height of half wavelength spiral arm length is about 65 mm.In order to reduce the antenna profile and realize miniaturization design,the traditional four arm helical antenna is optimized by phase-shift coupling chip loading,parasitic arm loading and dielectric loading.The final height of the antenna is less than 55 mm,and the VSWR is less than 1.4 in the operating band,and the radiation is not less than 1.5d Bi gain at 120° Angle,and the 3d B Axial Ratio specific beamwidth is more than 120°. |
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