Study And Design Of High Efficiency Large Aperture Reflector Compact Antenna Test Range System

Millimeter wave and terahertz technology has a wide application prospect in the fields of meteorology,astronomy and security check.However,in millimeter wave and terahertz band,the measurement of large aperture antenna system is facing a great challenge.Compact range can produce quasi plane waves in a small space,which is a reasonable and effective method to measure the antenna of meteorology,ocean,environment and deep space detector.This thesis presents a method of improving the aperture usage efficiency based on single reflector and triple reflector compact range,the system structure with high aperture usage efficiency is designed,and the correctness and effectiveness of the proposed method are verified by simulation and experiment.The main research work of this thesis is as follows:1.Firstly this thesis essentially studies the theory of parabolic aperture distribution field,and presents a theory to reversely compensate parabolic aperture distribution by illuminating it with a feed of shaped radiation pattern.Based on this theory,a coaxial cavity horn feed and a smooth wall horn feed are designed and implemented,which effectively compensate parabolic aperture distribution.The reflector edge diffraction effect is compared by setting cut-off region of the shaped waveform pattern and the offset structure of reflector surface is optimized.The quiet zone amplitude ripples<2 dB is achieved in the single reflector compact range,which verifies the correctness and effectiveness of the proposed theory,design method and the system architecture,and provides the base for the implementation of the large aperture single reflector compact range.2.As generally,the offset angle of the actual set up large aperture offset reflector is 30° or more,however,the beam width of the realized desired cos-4 form radiation pattern is only within the range of±20°.Under such condition,this thesis proposes a theory based on the high offset flat radiation pattern to approximate the shaped pattern characteristics in the high illuminating angle range according to the 3 m aperture single reflector compact range established at Queen Mary University of London.A coaxial cavity horn with flat pattern characteristic is designed and manufactured based on this theory.The feed system is set where the coaxial cavity horn is along the direction of the offset angle 55°to feed the 3 m reflector surface,and the quiet zone is measured.At 100 GHz,in the quiet zone aperture 2 m(66%aperture usage efficiency),the amplitude ripples of quiet zone are less than 2 dB.This indicates that the high efficiency large aperture parabolic single reflector compact range can be realized by being illuminated by coaxial cavity horn with flat radiation pattern in a high offset angle.In order to widen the single reflector compact range bandwidth,based on the high offset illumination theory,a smooth wall horn with broadband flat pattern features is set along the offset angle of 50° to feed the 3 m reflector,from 85 GHz to 105 GHz quiet zone aperture 2 m(66%aperture usage efficiency),the amplitude ripples of quiet zone are less than 2.5 dB.3.This thesis proposes an initial geometric layout condition of a offset tri-reflector compact range system based on a parabolic primary reflector,so as to obtain the tri-reflector compact range system with high cross-polarization isolation,without the need for cross-polarization control in the shaping process.The proposed initial geometric layout condition is adopted to design two tri-reflector compact range systems with the main reflector aperture of 3 m and 5 m,respectively.Within the range of the quiet zone,basically the main polarization amplitude ripples are less than 1 dB,phase ripples are less than 10°,and the cross-polarization isolation is more than 40 dB,thus providing the base for implementation of the large aperture high cross polarization isolation tri-reflector compact range system.Meanwhile,the splicing modes of large aperture reflector are studied in the spatial domain,time domain and angular domain,and the in:fluence of single panel movement on the performance of the quiet zone is analyzed to provide guidance for the actual setup work.4.Due to the spillover effect of the feed on the tri-reflector compact range system,this thesis studies the low sidelobe feed.Tanh contour is used to change the amplitude of the excited HE 12 mode at the aperture,and to ensure the minimum excitation of HE13 and higher order mode to achieve the low sidelobe simultaneously.Thus,a low sidelobe smooth wall horn with double profile of tanh/linear is designed and realized,and the measured sidelobe level is less than-3 7 dB.At the same time,a tanh/linear dual-profile corrugated horn is designed to realize the ultra-low sidelobe simulation level-50 dB and cross-polarization simulation level-64 dB.The two low sidelobe horns are used in the tri-reflector compact range system to weaken the spillover of the feed and improve the performance of the quiet zone.Moreover,the lower the sidelobe is,the smaller the amplitude ripples are in the quiet zone of the compact range,which provides high performance feeds for the large aperture tri-reflector compact range system.