Research On Ultra-Wideband Omnidirectional And Directional Antennas Borne On Vehicle

In recent years,the demand for high-performance antennas for communication systems of moving targets is increasing,such as tanks,armored vehicles,automobiles,etc.Whether in the military or civilian fields,traditional narrowband antennas can no longer meet the wide-band working requirements of vehicle antennas;On the other hand,the large size of the antenna is also difficult to meet the needs of the limited space installation of the vehicle platform.Therefore,the research on wideband and miniaturized vehicle antenna has high practical value for practical engineering,and it is also the main development direction of vehicle antenna.In this paper,two ultra-wideband vehicle antennas are developed according to scientific research projects and research topics.The research contents are summarized as follows:1.VHF/UHF frequency band composite integrated vehicle antennaA VHF/UHF frequency band composite integrated vehicle antenna suitable for military vehicle platform is designed.The two radiators of the VHF frequency band monopole antenna and the UHF frequency band dipole antenna are arranged coaxially and integrated,and the composite design of the VHF/UHF frequency band antenna is realized.The helical structure,the grounded sleeve structure and the top lumped network are simultaneously loaded on the monopole antenna,and the conformal planar biconical and stepped sleeve structure are loaded on the dipole antenna to widen the impedance bandwidth of the antenna;The coupling sleeve with frequency selection function is adopted to combin and share the radiators of the two frequency band antennas,which realizes the miniaturization and broadband design of the antenna;In order to improve the impedance matching of the antenna,a matching network is designed for the two frequency band antennas using the real frequency method.The research results show that the working frequency of the VHF band antenna(VSWR≤3.0)is 30～88 MHz,the working frequency of the UHF band antenna(VSWR≤3.0)is 108～678 MHz,and the radiation pattern remains omnidirectional in the horizontal plane in the entire frequency band.The antenna gain is greater than-7.5d Bi in the operating frequency range of 30-45 MHz,and the antenna gain is greater than-5d Bi in the operating frequency range of 45-88 MHz and 108-678 MHz,the overall size of the antenna is Φ 0.0062 λ × 0.16 λ(λ is the free space wavelength at 30 MHz).The proportional scaling model of the physical prototype is processed and tested.The test results of the physical prototype shows that the designed antenna has good omnidirectional characteristics in the horizontal plane pattern in the broadband range.2.Broadband dual-polarized antenna based on magnetoelectric dipoleThe first research work designed a single-polarized omnidirectional antenna,but the communication between the vehicle and the base station in the civil mobile communication system often requires a dual-polarized directional antenna.Therefore,how to realize the dual polarization and directional radiation pattern of the antenna in a wide frequency band is the main problem to be solved.Therefore,how to realize the dual polarization and directional radiation pattern of the antenna in the wide frequency band is the main problem to be solved in the second research work.A broadband dual-polarized antenna based on magnetoelectric dipole for civil vehicle platform is designed.The design of dual-polarized antenna is realized by placing two pairs of magnetoelectric dipoles orthogonally;A metal ring is loaded under the electric dipole to expand the impedance bandwidth of the antenna;The addition of annular side walls above the floor allows the antenna to have better directional radiation characteristics.The test result of the physical prototype shows that the operating frequency of the designed antenna(VSWR ≤ 2.0)is 0.74～2.44 GHz,and the relative bandwidth is 107%,which can cover the domestic 2G,3G and 4G mobile communication frequency bands.In the entire frequency band,the cross-polarization level is lower than-20 d B,and the front-to-back ratio is higher than 20.3d B.The antenna has good directional radiation characteristics.