Research On Low-Profile Dual Circularly Polarized Antenna Array

Since synthetic aperture radar(SAR)appeared in the 1950's,its development has attracted extensive attention.SAR is first used in military reconnaissance,and then resource exploration,precision navigation,meteorological observation,remote sensing and many other fields due to its high resolution and good image quality.SAR has broad prospects for development and research significance.Modern SARs develop in many directions,and different polarizations of multi-parameter SAR can significantly improve the detail and reliability of signals and images;Airborne SAR has put forward the requirements of miniaturization of antenna.Compared with linear polarization,circular polarization can detect more details of targets.And low-profile antennas have the advantage of light weight and low cost,especially for large antenna array,the characteristic of low-profile can significantly reduce the antenna's payload weight and the occupation of space.Therefore,low profile and circular polarized antenna is researched in this paper.The content of this thesis mainly includes the following aspects:(1)A patch antenna with back-cavity structure is designed.The capacitive coupling is used to widen the bandwidth.The dual-branch coupler produces equal amplitude and phase difference of 90°,so that the circularly polarized wave is synthesized by two orthogonal linearly polarized waves.By switching the input port of the coupler,the switching of left-handed and right-handed circular polarization can be realized.In order to improve the circular polarization performance of the array,the subarrays are formed by rotating elements to cancel the asymmetry of the physical structure.Part of the measured results of subarray match the simulation and the other results are studied.Taylor distribution amplitude weighting method is adopted to realize the low sidelobe requirement.The performance of 2x8 linear array and 6x6 planar array is analyzed.(2)Based on the high-impedance surface,which is the periodic structure,a low-profile microstrip antenna is designed.The improved orthogonal-dipole structure and the dual-branch coupler are used to form circular polarization.and the switching of left-handed and right-handed circular polarization can be realized.The feeding structure is air bridge.The HIS simulates the PMC as an antenna reflector to reduce the profile.The 2x2 sub-array and 2x8 linear array are formed by using sequentially rotating technology,which can improve the array's performance of circular polarization.(3)Based on the key frequency of the Beidou satellite navigation system,a multi-band antenna is designed,covering B1,B2 and B3.The modified orthogonal-dipole structure is adopted to realize the left-handed circular polarization.The formula of the return loss and isolation of the ideal bridge is obtained,with the known active S parameter.In order to determine the direction of incoming wave,the form of hexagonal array is adopted,and the performance of the array is simulated and analyzed.(4)Based on the established 5G experimental frequency band,a high isolation antenna with full coverage is designed,using a 3D printed plastic dodecahedron as the carrier.The antenna is installed on twelve faces of the dodecahedron,with high isolation between the units,The measured results are basically consistent with the simulation.