YBCO FERRITE LOW-LOSS MICROWAVE PHASE-SHIFTER

Microstrip-geometry phase shifters have limited use at microwave frequ encies because of high insertion losses resulting from resistance in t he metal conductors. We report a phase shifter fabricated from a YBa2C u3O7-x, microstrip line on LaAlO3 coupled to a ferrite toroid. The mag netic flux required for gyromagnetic interaction with the microwave si gnal is contained within the closed magnetic path of the ferrite toroi d so that the superconductor encounters a very low external magnetic f ield. Initial measurements at 77 K using a meanderline structure to pr ovide nonreciprocal operation have demonstrated greater than 700 deg o f differential phase shift at 10 GHz in a compact structure 2.5 cm lon g by 0.5 cm wide. The insertion loss is smaller than 0.7 dB which yiel ds a figure of merit considerably greater than 1000 deg/dB. The best c onventional phase shifters have an estimated figure of merit of 300 de g/dB at 77 K. Potential radar system applications and improvements in the figure of merit are discussed.