S-PARAMETER MEASUREMENTS AND MICROWAVE APPLICATIONS OF SUPERCONDUCTING FLUX FLOW TRANSISTORS

We have performed microwave two-port S-parameter measurements and modeling on superconducting flux flow transistors. These transistors, based on the magnetic control of flux flow in an array of high temperature superconducting weak links, can exhibit significant available power gain at microwave frequencies (over 20 dB at 7-10 GHz in some devices). The input impedance is largely inductive while the output impedance is both resistive and inductive. The characteristics are such that these devices are useful in numerous applications including matched amplifiers, phase shifters and active impedance convertors.