Optimization and design of a suspended 215–235-GHz subharmonically pumped mixer for space-borne radiometers

This paper presents the optimization and design of a low-loss fixed-tuned 215-235-GHz sub-harmonic mixer, pumped by planar GaAs Schottky diodes fabricated by European company for space-borne radiometers. The circuits are fully integrated with the RF/IF filter and flip-chipped onto a suspended quartz-based substrate. The GaAs Gunn oscillator is used as the local-oscillator (LO) and this paper also found an innovative nonlinear circuit model for GaAs Gunn diode in oscillator based on the physical mechanism. Its equivalent nonlinear circuit can assist the design of the Gunn LO. A best double-sideband-mixer loss of 6.4dB was achieved with 7mW of LO power at 224GHz. Over an RF band of 215-235GHz, the doublesideband loss is below 12dB. This state-of-the-art optimization is attributed to lower parasitic devices and a low-loss waveguide circuit.