Simple 1-mm receivers with fixed tuned double sideband SIS mixer and wideband InP MMIC amplifier

We report on attempts to broaden the IF bandwidth of the BIMA 1mm SIS receivers by cascading fixed tuned double-sideband (DSB) SIS mixers and wideband MMIC IF amplifiers. To obtain the flattest receiver gain across the IF band we tested three schemes for keeping the mixer and amplifier as electrically close as possible. In Receiver I, we connected separate mixer and MMIC modules by a 1" stainless steel SMA elbow. In Receiver II, we integrated mixer and MMIC into a modified BIMA mixer module. In Receiver III, we devised a thermally split block where mixer and MMIC can be maintained at different temperatures in the same module. The best average receiver noise we achieved by combining SIS mixer and MMIC amplifier is 45 -50 K DSB for νLO = 215 - 240 GHz and below 80 K DSB for νLO = 205 - 270 GHz. The receiver noise can be made reasonably flat over the CARMA IF band (νIF = 1 - 5 GHz). Noise temperatures for all three receivers are comparable to or better than those obtained with the BIMA receiver.