Design of a Sideband Separating Receiver for 500 GHz

We describe design of a sideband-separating superconductor-insulator-superconductor (SIS) mixer for the APEX telescope Band 3, 385 – 500 GHz. The mixer design combines waveguide components and on-chip local oscillator (LO) injection. The receiver used quadrature scheme where the RF signal is divided equally with a 90-phase shift by a waveguide 3 dB hybrid with novel design using several microstrip probes. The LO is divided using an in-phase or 180degree waveguide E-plane Y-junction. The output waveguides of the hybrid are coupled to the mixer SIS junctions through an E-probe based on waveguide-to-microstrip transition with integrated bias-T. A directional coupler for the LO and RF signals, the SIS junction, the tuning circuitry lines and the biasT are integrated on a single mixer chip. We use a novel component, an ellipse termination to provide easy and highperformance on-chip LO injection. Index Terms — SIS mixer, sideband separating receiver, waveguide-to-microstrip transition.