Noise and conversion properties of Y-Ba-Cu-O Josephson mixers at operatingtemperatures above 20 K

We have measured the noise performance and conversion efficiency of Y-Ba-Cu -O bicrystal Josephson mixers at operating temperatures between 20 and 60 K and at operating frequencies around 90 GHz. A double-sideband mixer noise temperature of about 1600 K and a conversion efficiency of -10 dB at 20 K o perating temperature has been measured using the Y-factor method. The absor bed local oscillator power was in the range of 10 nW. The dependence of the mixer performance on the normalized frequency Omega and the fluctuation pa rameter Gamma has been studied. In accordance with the resistively shunted junction model, the experimental data show the presence of excess noise. Th e temperature dependence of the mixer noise temperature can be explained by the variation of the linewidth of the Josephson oscillations with the oper ating temperature. (C) 2000 American Institute of Physics. [S0003-6951(00)0 0113-3].