A 220-GHz Cryogenic Quasi-Optical Schottky Subharmonic In-Phase Quadrature Demodulation Receiver

This article presents a 220-GHz cryogenic quasi-optical Schottky subharmonic in-phase quadrature (IQ) demodulation receiver for terahertz (THz) applications. To achieve spatial separation of the local oscillator and radio-frequency coupling signals, we propose a dual-band dual-beam antenna, comprising a monopole lens antenna and a microstrip patch array. Such quasi-optical coupling design not only facilitates thermal isolation for cryogenic electronic systems, but also avoid the beam-splitter losses endured by conventional quasi-optical receivers, thereby maximizing system performance. Moreover, we propose a compact IQ demodulation circuit design based on the dual-band quadrature hybrid, which features reduced complexity and lower insertion loss as compared with traditional approaches. A prototype of 220-GHz cryogenic quasi-optical Schottky subharmonic IQ demodulation receiver was fabricated and experimentally verified at 60 K. Operating over a RF bandwidth of 212–228 GHz, the receiver has a measured average single-sideband (SSB) conversion gain of around -12 dB and double-sideband (DSB) noise factor of around 3 dB for the I or Q output, respectively. These results have demonstrated the superior receiver performance and its application potentials.