A five-frequency bands quasi-optical multiplexer for geostationary orbit microwave radiometer

Microwave radiometer on board the FY-4 microwave satellite, which is China's second generation geostationary orbit meteorological satellite, is able to acquire temperature profiles and humidity profiles at 54, 118, 183, 380 and 425GHz. The FY-4 microwave radiometer receives the radiation emitted by the earth surface and atmospheric molecules at the five-frequency bands. A multiplexer is an important part of the radiometer, which separates the radiation beam into five-frequency bands signal and transmits the signal to respective receiver of each frequency band. In this paper, a five-frequency bands quasi-optical multiplexer is designed for the low-loss frequency band separation. Meanwhile, the quasi-optical multiplexer seen as a feed network of the radiometer has to provide the proper antenna illumination in amplitude and phase for the antenna reflector. Quasi-optical techniques are used to design the overall five-frequency bands multiplexer.