Any device used to multiply signals which has a nonlinear response to an electric field. Possible devices include bolometers, photoconductors, classical (Schottky) diodes, and quantum non-linear devices (SIS receivers or Josephson junction mixers). Bolometers and photodetectors have limited response time and therefore limited IF bandwidths. Classical diodes cannot have gain and typically have I-V characteristics whose nonlinearity involves a semiconductor gap of V. Quantum nonlinear devices can have gain, and have a superconducting gap of a few mV, as well as having low power requirements (Phillips 1988).
Heterodyne Conversion, Local Oscillator, Sideband
References
Phillips, T. "Techniques of Submillimeter Astronomy." 1988.
