A 3:1 bandwidth planar, lossless cavity backed sinuous antenna for reflector feed applications

An ultra-wideband, dual polarized printed cavity backed sinuous antenna with a 3:1 matched bandwidth ratio is presented. The antenna is characterised as a feed for a prime focus paraboloid reflector and as a feed in an offset Gregorian configuration. A parameter study is performed using full wave simulations, and the effects of, and bounds on the main design parameters are described. A prototype antenna is designed, with a simulated aperture efficiency of about 58% for an offset Gregorian reflector antenna, whilst having a measured return loss of 10 dB or better over a 3:1 bandwidth.