Optimizing the Cross Polarization Performance of a Compact Test Range by Conjugate Matched Field Concept

Single reflector and dual cylindrical reflector Compact Test Ranges (CTRs) are well known for having a high cross-polarization level in the quiet zone (QZ), limiting their measurement performance. A new three element feed array is developed. By adding two adjacent open waveguide antennas a conjugate matched field is generated leading to a superposed field in the QZ, having lower cross-polarization level. The ideal excitation values for each element is calculated by a nonlinear, numerical optimization, which also considers the limited performance of the experimental feeding network. A validation of the feed array concept is done by field probe scans in the CTR of the German Aerospace Center (DLR), showing an improvement of better than 8 dB over 900MHz in the X-band.