115 GHz Low Noise Cryogenic Receiver for Radioastronomy

This paper describes a cryogenic front-end designed for radioastronomical observations around 115 GHz. The system includes an image-rejection filter, a single ended microstrip mixer, and a 5 GHz IF consisting of a paramp followed by a FET amplifier, all cooled at 20°K and 77°K. The mixer uses state of the art GaAs Pt/Au Schottky diodes. Modular construction using microstrip techniques allows an easy replacement of the diode. Design and construction aspects are discussed, with emphasis on scaling methods and problems associated with cooling. Measurement methods are described. Individual stage and overall performance results are presented.