Development of a X-Band, Crosspolarization Compensating Feed Antenna for the Compact Test Range

Abstract

In antenna measurements it is well known that single reflector and dual cylindrical reflector Compact Antenna Test Ranges (CATRs) suffer from a high cross-polarization level in the Quiet Zone (QZ). This limits their performance of measuring an Antenna under Test (AUT) with high cross-polar suppression. This issue is avoided by the development of a new three element feed array. The central horn antenna ensures the co-polar field, while the outer horns generate the so called conjugate matched field and hence reduce the cross-polarization. A nonlinear, numerical optimization is used to calculate the weighting factors of each element. It must consider also the limitations of the prototype-based feeding network. The feed array is capable of generating horizontally and vertically polarized waves and it operates in the X-band. The performance of the feed array is validated in High-Frequency Structure Simulator (HFSS) simulations, where an improvement of 8 dB in the cross-polar level is found in the QZ. A proof of concept demonstrator is measured in the Compact Test Range (CTR) of the Microwaves and Radar Institute of the German Aeorspace Center (DLR). A field probe scan shows a mean cross-polar level of −41.6 dB, over 9 dB better than the currently used reference. The cross-polarization is effectively reduced over a bandwidth of 900 MHz.