Validation of design techniques on a quasi-optics test bench

A two channel Quasi-Optics Network (QON) with a Frequency Selective Surface (FSS) to act as filter has been designed, constructed and tested in order to examine several aspects of the design, including the accuracy of the design software, the effectiveness of the FSS and the effect of moving components along the ray path in a QON. The QON was designed to feed an offset reflector system which required an input beamwidth of 20 degrees at -8.68 dB. The two channels were the atmospheric sounding channels at 54 GHz (5 GHz bandwidth) and 89 GHz (3 GHz bandwidth). Gaussian beam techniques were used to design the QON with the final optimisation carried out using Physical Optics and Physical Theory of Diffraction. The measurements were carried using the facilities at National Physical Laboratory, London and Queen Mary, University of London. Agreement between predicted and measured performance was good, thus validating the design method, the equipment manufacture and the assumptions.