Research And Design Of S-band Circularly Polarized Antenna For Vehicle

Circularly polarized antenna has great advantages for radar tracking,global positioning system?GPS?,satellite communication,radio frequency identification?RFID?and sensor system,because circularly polarized wave can reduce the multipath effect and the orientation angle between transmitter and transmitter.In recent years,various compact circularly polarized antennas have been developed for portable and mobile terminal applications.On the other hand,because the satellites of the navigation system mostly operate in the orbit of the earth,the angle range of the receiving antenna for positioning service is very wide,usually between the zenith with?=0°and the low elevation angle of the ground with?=70°.Within this angle range,a certain gain is needed.Therefore,the mobile communication satellite system has strict requirements for the gain of the antenna with the function of receiving and transmitting electromagnetic wave at the beam width and low elevation.In this paper,based on the research and design of the vehicle antenna receiving the signal of tiantong-1 satellite,the existing problems in beam width,elevation gain and miniaturization of the antenna are studied and discussed.In this paper,several kinds of antennas used in automobile scene are studied.The specific work includes the following aspects:Firstly,a high gain circularly polarized planar helical antenna is designed.In this structure,the dual arms of Archimedes spiral antenna are fed by microstrip gradual balun with wide working frequency band.By adding an improved flat bottom reflector structure at the bottom of the antenna,and loading a medium plate with high refractive index on the upper side of the antenna radiator,the antenna achieves a high gain directional radiation at an elevation of 30°⁹0°.The final simulation results show that the VSWR is less than 1.2,the half power beam width is greater than 86°,the 3dB axial ratio beam width is greater than 140°,the circular polarization gain of 30°⁹0°elevation is increased by 0.5¹.5dB,the gain of 40°elevation is greater than 2.8dB,and the gain of 30°elevation is greater than 1.5dB.This kind of antenna is more suitable for the satellite mobile communication of vehicles in the low latitude area of the whole country.Then,a low profile wide beam circularly polarized microstrip antenna is designed.The radiator of the antenna is in the form of 2×2 sequential rotating microstrip array.Four linear polarization elements are fed by the sequential rotating feed,and the series equal power distribution feed network is used for feeding.The overall profile of the final antenna is only 0.068?₀,the half power beam width is 114°,and the 3dB axial ratio beam width is greater than 160°.This kind of antenna has low profile,easy installation and little wind resistance,so it is suitable for high-speed moving ground carrier.Finally,a wideband and wide beam circularly polarized dipole antenna is designed.The structure of the antenna is to introduce four parasitic magnetic dipole elements between the cross electric dipole patch elements and the short circuit metal wall.The complementary principle of the electric and magnetic dipole antenna pattern is used to make the antenna radiate evenly in the upper half of the space and expand the width of the lobe,so as to improve the gain at the low elevation.In addition,due to the parasitic element loading,the current path on the cross dipole arm is extended,so that the antenna profile is reduced to 0.13?₀.The results show that 65%of the impedance bandwidth can be obtained when the VSWR is less than 2,the gain is greater than 3dB when the VSWR is less than 1.4 and the elevation angle is 30°,the half power beam width is greater than 115°and the 3dB axial ratio beam width is greater than 200°.This antenna is suitable for satellite mobile communication in high latitude area of our country.