Design of a Sideband-Separating Balanced SIS Mixer Based on Waveguide Hybrids

We describe a design for a sideband-separating balanced mixer using four planar single-ended mixer chips connected to the feed horn and LO source by a network of quadrature waveguide hybrids and an in-phase waveguide power divider. The mixer has separate IF output ports for the downconverted signals from the upper and lower RF sidebands, and requires ~14 dB less LO power than a single-ended mixer using a 20-dB LO coupler. The design of the mixer is suitable for scaling to ~700 GHz and can be fabricated using CNC machining techniques.