YBCO FERRITE LOW-LOSS MICROWAVE PHASE-SHIFTER

Microstrip-geometry phase shifters have limited use at microwave frequencies because of high insertion losses resulting from resistance in the metal conductors. We report a phase shifter fabricated from a YBa2Cu3O7-x, microstrip line on LaAlO3 coupled to a ferrite toroid. The magnetic flux required for gyromagnetic interaction with the microwave signal is contained within the closed magnetic path of the ferrite toroid so that the superconductor encounters a very low external magnetic field. Initial measurements at 77 K using a meanderline structure to provide nonreciprocal operation have demonstrated greater than 700 deg of differential phase shift at 10 GHz in a compact structure 2.5 cm long by 0.5 cm wide. The insertion loss is smaller than 0.7 dB which yields a figure of merit considerably greater than 1000 deg/dB. The best conventional phase shifters have an estimated figure of merit of 300 deg/dB at 77 K. Potential radar system applications and improvements in the figure of merit are discussed.