Wide-Band, Ultra Low Noise MM-Wave Mixers with a Single Tuning Element

Several SIS quasiparticle mixers have been designed and tested for the frequency range from 80 to 115 GHz. The sliding back short is the only adjustable RF-tuning element. The RF-filter reactance is used a s a fixed RF-matching element. A mixer which uses a single 2 × 2 ¿m2 Pb-alloy junction in a 1/4-height waveguide mount has a coupled conversion gain of GM(DSB) = 2.6 ± 0.5 dB with an associated noise temperature of TM(DSB) = 16.4 ± 1.8 K at the best DSB operation point. The receiver noise temperature TR(DSB) is 27.5 ± 0.8 K for the test apparatus. This mixer provides a SSB receiver noise temperature below 50 K over the frequency range from 91 to 96 GHz, the minimum being TR(SSB) = 44 ± 4 K. Another mixer with an array of five 5 × 5 ¿m2 junctions in series has much lower noise TM(DSB) = 6.6 ± 1.6 K, but less gain GM(DSB) = ¿5.1 ± 0.5 dB.