Noise temperature measurement of YBCO Josephson mixers in millimeter and submillimeter waves

We have investigated YBCO step-edge Josephson junctions as millimeter and submillimeter wave mixers. These mixers were integrated with an Au thin-film log-periodic antenna designed for broadband coupling of the radiation. We estimated the noise temperature of the mixer using conventional hot/cold blackbody irradiation techniques in the 100- and 300-GHz bands. We found that the Au thin-film antenna yielded about 5 dB higher coupling efficiency than that of YBCO thin film antenna, and the noise temperature decreased from 2,800 K to 1,800 K. The best receiver noise temperature, 1,200 K, was achieved in the 300-GHz band through improvement in impedance matching.