A HYBRID PHASE-SHIFTER CIRCUIT BASED ON TLCABACUO SUPERCONDUCTING THIN-FILMS

A superconductor-semiconductor hybrid reflection-type phase shifter ci rcuit has been designed, fabricated, and characterized for 180 degrees phase bit with center frequency of 4 GHz and bandwidth of 0.5 GHz for operation at 77 K, All of the passive components of the phase shifter circuit such as input/output feed lines, 3 dB Lange coupler, impedenc e matching networks, and transmission lines consisted of thallium base d superconducting TlCaBaCuO thin films of 4000 Angstrom thickness on l anthanum aluminate substrate, Metal-Schottky field-effect transistors (MESFET's) on GaAs semiconductor were used as active devices for switc hing action (on-state and off-state) in the phase shifter circuit, The phase shift and insertion losses were investigated as a function of f requency from 3.6 to 4.6 GHz at 77 K, The circuit exhibited a fairly f lat response of 180 degrees phase shift with a maximum deviation of le ss than 2 degrees and a maximum insertion loss of 2 dB for on-state an d 2.2 dB for off-state conditions over 0.5 GHz bandwidth at 4 GHz, The insertion losses were also fairly flat within the bandwidth, The inse rtion losses were constant between 50 and 80 K, giving the circuit a l arge range of operation at or below 77 K, The performance of this circ uit as compared to a gold microstrip-semiconductor circuit designed id entically was superior by a factor of 1.5, and may be due to lower con ductor losses and lower surface resistance in the superconducting micr ostrips.