Ce. Honingh et al., EXTENSIVE TEST OF THE 3-PORT QUANTUM MIXER THEORY ON 345 GHZ SUPERCONDUCTOR-INSULATOR-SUPERCONDUCTOR MIXERS, Journal of applied physics, 74(7), 1993, pp. 4762-4773
Predictions of the three-port model of the quantum theory of mixing ar
e compared with measured results on 345 GHz superconductor-insulator-s
uperconductor waveguide mixers. Single Nb-Al2O3-Nb tunnel junctions or
two or four identical junctions in series are used as mixing elements
. Two different waveguide mixerblocks, one with two tuners and another
with one tuner, are used. In addition a single junction with integrat
ed tuning stub is analyzed. Embedding impedances are obtained from fit
s to the pumped I-V curves for all three types of mixing elements. In
all cases the dependence of mixer conversion and mixer noise on bias v
oltage, pump power, and embedding impedance is well described by the t
hree-port model. The measured mixer gain is lower than the calculated
gain by a factor of 0.35-0.65, independent of the type of mixer. The u
se of an additional integrated tuning element does not change this fac
tor. It is concluded that an excess noise power equivalent with a blac
kbody source of 40-65 K must be added to the mixer noise to account fo
r the absolute value of the observed noise power.