Tunerless mixer mount for an SIS 80–120 GHz receiver

We have developed a 100 GHz band SIS receiver using a simple mixer mount design, which does not use variable RF tuning elements, such as a back short tuner or an E-plane tuner. The mixer mount structure was designed using calculations of the embedding impedance of the mixer mount, and of receiver performance, using the quantum theory of mixing under the 3-port approximation. The mixer mount structure we designed has a 1/7 reduced height waveguide and a “back short cavity”. We have constructed a receiver system using this tunerless mixer mount design, and we have measured the receiver noise temperatures for two different tunerless mixer mounts using arrays of four Nb/Al-AlOx/Nb junctions. For one of the two mixer mounts, we obtained very low noise receiver temperatures, 35–70 K, over the very wide frequency range of 80–120 GHz. We also show that, due to IF missmatching, the noise of the IF amplifier is the main contributor to the receiver noise temperature. We also compared the results of measurements with the results of our theoretical calculations. Our calculations reproduced the tendency of receiver performances very well. This tunerless mixer mount has application on the MM-Wave Array and in the multi-beam receiver.