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 conv entional 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 th e noise temperature decreased from 2,800 K to 1,800 K. The best receiv er noise temperature, 1,200 K, was achieved in the 300-GHz band throug h improvement in impedance matching.