A novel broadband Q-band polarizer with very flat phase response

We present a 33-50 GHz circular waveguide polarizer based on a broadband combination of retarders. The device was designed within the FP7 RadioNet APRICOT (All Purpose Radio Imaging Cameras on Telescopes') consortium for the development of focal plane arrays for radiotelescopes. The device is based on a Pancharatnam recipe used in optics and behaves as a polarization transformer, from circular to linear and vice versa. This novel design of polarizer exhibits an unprecedented performance combining extremely flat differential phaseshift across the whole band, very low losses and very low Amplitude Unbalance (AU). It can be used in astronomical instruments or telecommunication antennas where very high purity circular polarization is required. The design was manufactured and then tested using a Vector Network Analyzer (VNA). Averaged across a 40% bandwidth the measured RL, IL, amplitude unbalance and differential phase-shift were respectively: -31.4/-35.3 dB, -0.09/-0.06 dB, 0.04 dB and 90.0 ± 0.4 o.