Research On Conjugate Matched Feed Based On Offset Single Parabolic Reflector CATR

Compact antenna test range(CATR)is an important technology in the field of antenna testing,which can achieve measurement of antenna parameters at close range.It plays an important role in measuring electrically large antennas in the millimeter wave and terahertz frequency bands.Offset parabolic reflector CATR has the advantages of simple structure,easy processing,and low cost.However,the quiet zone(QZ)usage of the single reflector CATR is generally only 30%.Even if edge treatment is carried out on the mirror surface to reduce the impact of edge diffraction on the static zone,the QZ usage is only increased to about 50%.The current research has proven that the asymmetric coaxial cavity horn feed can radiate a nearly ideal biased pattern,thereby improving the QZ usage of the single reflector CATR.However,at this time,the crosspolarization isolation of the system is only slightly higher than 20dB,and further improvement is still needed.Therefore,improving the QZ usage of the single reflector CATR while improving the cross-polarization isolation of the system has become the focus of this study.Based on the existing theory of the CATR of a biased single parabolic reflector and the conjugate matching theory of a biased reflector antenna,this paper first proposes a conjugate matching feed theory based on the CATR of a biased single parabolic reflector.The amplitude radiation density functions of the main polarization and cross polarization of the conjugate matched feed source with ideal bias pattern were obtained.And the correctness and effectiveness of this method in improving both static zone utilization and cross polarization isolation were verified through numerical simulation.This provides theoretical guidance for the design of actual feed sources.Afterwards,this article designed a three-pin coaxial cavity horn feed.The feed utilizes three-pin to introduce a suitable TE21 mode,which forms a conjugate match with the cross polarization of the single reflector CATR,thereby improving the cross-polarization isolation of the system;At the same time,the three-pin structure was used to offset the main polarization radiation of the feed.After optimizing the structural parameters,the design of the biased feed shaping pattern was achieved,thereby achieving the goal of improving the QZ usage of the single reflector CATR.From the simulation results,it can be seen that this feed not only improves the QZ usage of the single reflector CATR to 70%,but also increases the crosspolarization isolation of the system to more than 30dB.Finally,the designed feed source was processed and tested,and also incorporated into the single reflector compact field system established by the simulation software GRASP.The results showed that the measured feed data improved the QZ usage of the system to 60%,and the cross-polarization isolation degree to 26.58dB.