REGARDING THE IF OUTPUT CONDUCTANCE OF SIS TUNNEL JUNCTIONS AND THE INTEGRATION WITH CYROGENIC InP MMIC AMPLIFIERS

There is a strong interest in the Submillimeter community to increase the IF bandwidth of SIS receivers in order to facilitate extra-galactic astronomy. However, increasing the IF bandwidth generally also means increasing the IF operating frequency of the mixer, because it is very difficult to achieve a good IF impedance match to a low noise amplifier (LNA) for more than an octave bandwidth. Complicating the matter is that most cryogenic amplifiers do not have a very good input match, which nearly always results in severe standing waves between the mixer and amplifier, especially since the amplifier is connected to the mixer via a finite (10 cm) length of coaxial line. The use of a cryogenic isolator would eliminate the standing wave issue, however all of the currently available cryogenic isolators have less than an octave of bandwidth. The second approach would be to integrate a low noise amplifier into the mixer block, minimizing the distance between the junction and LNA. In this paper we investigate the SIS junction’s IF output conductance and the possible integration of SIS mixers with InP MMIC low noise amplifiers, as an alternative to the traditional matching network/isolator approach. In particular we look into the use of a grounded Gate and grounded Source configured low noise InP amplifier, and the performance one is likely to achieve.