Superconducting variable phase shifter

A superconducting variable phase shifter providing improved performance in the microwave and millimeter wave frequency ranges. The superconducting variable phase shifter includes a transmission line and an array of superconducting quantum interference devices (SQUID's) connected in parallel with and distributed along the length of the transmission line. A DC control current IDC varies the inductance of the individual SQUID's and thereby the distributed inductance of the transmission line, thus controlling the propagation speed, or phase shift, of signals carried by the transmission line. The superconducting variable phase shifter provides a continuously variable time delay or phase shift over a wide signal bandwidth and over a wide range of frequencies, with an insertion loss of less than 1 dB. The phase shifter requires less than a milliwatt of power and, if one or more of the Josephson junctions fails, the whole device remains operational, since the SQUID's are connected in parallel.