Measurement of the noise contributions to SIS heterodyne receivers

The development of quantum limited heterodyne receivers requires that you understand and are able to measure the major sources of noise in the receiver system. The major sources of noise in millimeter- and submillimeter-wave SIS heterodyne receivers are the optical front end losses, vacuum fluctuation noise associated with the RF coupling efficiency to the SIS tunnel junction and IF amplifier noise. Although there are several methods for estimating the optical losses and IF amplifier noise, the RF coupling efficiency or quantum efficiency has been much more difficult to ascertain. This paper describes in situ techniques for measuring all three noise contributions in a standard receiver used for astronomical observations. Results are presented for the receivers operating in the Owens Valley Millimeter Interferometer Array.<
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