SUPERCONDUCTING BOLOMETRIC MIXERS

Mixing at 20 GHz in niobium superconducting thin-film strips in the re sistive state is studied. Experiments give evidence that electron-heat ing is the main cause of the nonlinear phenomena. The requirements on the mode of operation and on the film parameters for small conversion loss and the possibility of conversion gain are discussed. Measurement s indicate a conversion loss between 1-8 dB and a DSB mixer noise temp erature between 100 and 450 K at 20 GHz. The device output noise tempe rature at the mixer operating point can be as low as 30-40 K. A simple theory that is based on the assumption that the small signal resistan ce is linearly dependent on power is presented. This type of mixer is considered very promising for use in low-noise heterodyne receivers at THz frequencies.