A waveguide structure is presented for the RF front end of a sideband-separating heterodyne receiver operating in the 0.8–1 mm band, based on two single-ended superconductor–insulator–superconductor (SIS) mixers. The microwave properties of the following elements are investigated: a 90° quadrature hybrid, a directional coupler, a T-junction power divider, and a transition section; their amplitude and phase frequency responses are calculated. For the 90° hybrid, the amplitude imbalance does not exceed 1.5 dB, the phase imbalance including reflections stays within 2°, and both return loss and isolation are better than –25 dB. In addition, a full waveguide assembly was simulated with the SIS-mixer reflections taken into account. The resulting sideband rejection of the entire waveguide structure, including mixer reflections, is no worse than 20 dB across the band.
Nazarov et al. (Wed,) studied this question.