Superconductor ferrite phase shifters and circulators

We have previously demonstrated high-T/sub c/ superconductor/ferrite nonreciprocal microwave phase shifters that avoid dc magnetic-flux penetration of the superconductor through a novel design of the magnetic circuit, and thus operate with very low loss. Recently, a simplified magnetic structure has been introduced, and devices with approximately 0.1 dB insertion loss with 500 degrees of phase shift (figure of merit 5000 deg/dB) at 10 GHz and 77 K using YBCO have been demonstrated. The same operating principles have been applied to the design and fabrication of circulators. By combining three low-loss phase shifters and three T junctions on a ferrite substrate in a configuration with three-fold symmetry, a three-port switching circulator has been demonstrated using niobium at 4 K. The insertion loss is less than 1 dB, the isolation greater than 20 dB, and switching time less than 1 /spl mu/s. The switching circulator can serve as a low-loss, high-speed rf switch. Extension of this design to YBCO is discussed. Higher performance, reduced weight and volume, as well as lower cost are anticipated for microwave systems that can benefit from such circulators and phase shifters.