ANTENNA-COUPLED SUPERCONDUCTING CONTACTS IN SUBMILLIMETER AND FIR ASTRONOMY

Advantages and restrictions of an antenna coupled superconductor-isola tor-superconductor (SIS) detector are discussed at the example of a 34 5 GHz open structure receiver. At submillimeter wavelengths an antenna coupled mixer is cost effective and provides ultimate bandwidth. Hete rodyne systems with large IF bandwidth can challenge He-3 bolometers f or continuum work. The status of open structure mixers in astronomy is presented. A noise budget based on a mathematical receiver model is i n agreement with the measured receiver noise. An antenna coupled SIS d etector in a dipole-lens combination has less beam efficiency than a w aveguide mounting. As its sensitivity is equally good or better it mak es up for its lack in efficiency by a higher transmission. If the junc tion capacitance is resonated out by a superconducting matching circui t, SIS mixers can approach the quantum noise limit. Fully assembled SI S receivers work at a few times this limit due to unavoidable losses i n the signal path. Their application at frequencies up to 1 THz would be appealing for astronomy. A key role in this effort play efficient s uperconducting matching circuits which can handle the large static cap acitance of junctions at operating frequencies much higher than the RC limited corner frequency. Niobuimnitride is a superconductor which ex ceeds the frequency limit of Niobium. The prospects of this material a re addressed and first results are presented.