Dynamic Range of High Temperature Superconducting Josephson Detecting Systems at Millimeter-Wave Band

Abstract

YBCO grain boundary Josephson junctions (GBJJ's), with the normal-state resistance (R/sub N/) around 1 /spl Omega/ and I/sub C/R/sub N/ product of less than 2 mV at 45 K, where I/sub C/ is the critical current of the junction, are used to study the dynamic range of high temperature superconducting (HTS) Josephson detecting systems at millimeter-wave band. A compact pulse tube cryocooler (PTC), or a liquid helium cryostat (LHC), or a liquid nitrogen cryostat (LNC) provides the necessary low temperature environment for the operation, while Gunn oscillators together with doubler generate signals at the frequencies of 50, 98, 196 GHz whose amplitude can be adjusted by a series of calibrated attenuators. By changing the junction parameters, operating frequencies, and the cryocooler or cryostat, we have carefully looked at the dynamic range of the system. For a measuring channel bandwidth of 1 Hz, the dynamic range is around 38 dB which is determined basically by the preamplifier. This indicates that the PTC does not introduce excess noise compared with other kinds of cryostats such as LHC's or LNC's. A measuring channel bandwidth up to 1 MHz can be helpful if fast measurements are needed.