Sensitivity of high temperature superconducting Josephson detectors at millimetre-wave band

Abstract

Sensitivity of high temperature superconducting (HTS) Josephson detectors at millimetre-wave band has been studied in detail. YBCO grain boundary Josephson junctions with the normal-state resistance (RN) around 1 Ω and ICRN product of less than 2 mV have been fabricated for this study, where IC is the critical current of the junction. A Gunn oscillator at the frequency of 98 GHz together with a set of calibrated attenuators with a total attenuation of 90 dB are used as a signal source. A quasi-optical system, which consists of a wideband planar log-periodic antenna encompassing the junction, parabolic mirrors and a hyperhemispherical silicon lens, has been used as an effective coupling system. Sensitivity increases with ICRN. Using a junction with ICRN of 300 µV, a sensitivity of about 9000 V W−1 has been obtained, which is higher than that of the Schottky diode detectors at the same frequency band and demonstrates that the HTS Josephson detectors are very sensitive at millimetre-wave band.