Optimisation of cross-polarisation performancefor tri-reflector CATRwith spherical main reflector

For a tri-reflector compact antenna test range (CATR) with spherical main reflector and shaped subreflectors, the cross-polarisation performance is optimised, based on the beam-mode expansion method. For optimal designs, physical optics (PO) calculations of the quiet zone fields are presented, and it is shown that a tradeoff has to be made between a low cross-polarisation level and a low amplitude ripple in the quiet zone.