Validation of Design Techniques on a Quasi-Optics Test Bench
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Validation of Design Techniques on a Quasi-Optics Test Bench P. R. Foster & P. A. R. Ade & R. Donnan & J. Dupuy & J. McNiff
Received: 30 March 2007 / Accepted: 19 April 2007 / Published online: 4 May 2007 # Springer Science + Business Media, LLC 2007
Abstract 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. Keywords Quasi-Optics . Gaussian beam . Atmospheric sounder channels . Validation
1 Introduction The work described in this paper has been generated by the current and future requirements of space-borne microwave and millimetric instruments, particularly for earth observation. In P. R. Foster (*) Microwave and Antenna Systems, Peachfield Road, Malvern, UK e-mail: [email protected] P. A. R. Ade Department of Physics and Astronomy, University of Cardiff, Cardiff, UK R. Donnan : J. Dupuy Queen Mary, University of London, London, UK J. McNiff Sula Systems, Wotton-under-Edge, Gloucestershire, UK
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Int J Infrared Milli Waves (2007) 28:521–529
such instruments, the number of reflectors has to be kept to a minimum, due to weight and size limitations, and there is a requirement to accommodate a number of narrow emission bands spread sparsely over a wide frequency range. One approach to the design of the reflector feed system is to use a Quasi-Optics Network (QON). Using a QON to separate the multiple frequencies has the advantage that the output beams from the reflector are collocated, which leads to better beam efficiency, although resistive losses may be greater than for a cluster of separate feed horns in the reflector focal plane. The total frequency band of in-service QONs is not much more than 2:1 (AMSU-B, [3]). Apart from a few test builds of equipment (for example, a multi-channel QON in the MASTER program [1, 2]), few examples of other working systems have been built. The design requirements for earth observation spacecraft have become much more demanding over the last fifteen years. In particular, there are many more frequency channels covering a much greater total frequency range to be accommodated in one instrument The result is that the design of QON systems has to be pu
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