Noise temperature study of weak-link josephson junction array mixers in a mm-wave range

摘要

We have estimated the noise temperature of high-T_c grain boundary Josephson junctions on an MgO bicrystal substrate at 100 GHz by two methods. A single junction has a noise temperature almost equal to its physical temperature when it is determined by the analysis based on the RSJ model. However, an array of 5 Josephson junctions has a noise temperature by a factor of 27 larger than a single junction. The radiation heating and the external noise effect are relevant in these estimates. When the Y-factor method is employed, the mixer noise of the 5-Josephson-junction array is estimated to be 20,000 K at 100 GHz. The relationship between the estimates is discussed.