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This paper describes techniques that have been investigated in order to minimise RF interference effects between a 35.5GHz radar and a multi-frequency radiometer with one of its bands operating around 36.5 GHz. One of the main potential interference paths identified is direct coupling between the instruments' antennas: both instruments have high-gain, earth pointing reflector antennas. The instruments are to be accommodated on a small satellite and, unlike large multi- instrument platforms, it is not possible to use the satellite structure to isolate them. The radiometer antenna is scanned mechanically over a large sector and there are no feasible options for introducing baffles or shields in order to reduce the antenna coupling factor. Instead, techniques that have been looked at include frequency-domain filtering and time-domain blanking. Blanking is achieved using a PIN switch to isolate the input to the radiometer channel during the period when the radar is transmitting. Whilst the approach can reduce the effects of interference to acceptable levels there is the potential for the PIN switch to degrade the radiometer's performance in other ways. Although such switches have been used in Dicke switch radiometers there is little reported information on their use in total power radiometers as is proposed here. Therefore a programme of tests was conducted to investigate the stability and repeatability of a PIN switch placed in the front-end of a representative radiometer. These tests, the results obtained and the conclusions drawn are reported on.
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