We report on the design, fabrication, and testing of novelYBa2Cu3O7−&dgr;/SrTiO3/LaAlO3(YBCO/STO/LAO) andAu/SrTiO3/LaAlO3(Au/STO/LAO) coupled microstrip line phase shifters (CMPS). These CMPS were tested at frequencies within the Ku and K bands (12–20 GHz), at temperatures from 24 to 77 K, and at dc voltages(Vdc)from zero to 350 V. A relative insertion phase shift (&Dgr;&fgr;) of 390° was measured for an eight-element YBCO/STO/LAO CMPS atVdc=350 V,16 GHz, and 40 K. At 77 K, a&Dgr;&fgr; ∼260°was obtained for the CMPS at the same bias and frequency. Both results correspond to an effective coupling length of 0.33 cm. At both temperatures, the phase shifter exhibits a figure of merit of∼30°/dB.To our knowledge, these are the best results published so far at these frequencies where miniaturization, insertion loss, and phase delay are key considerations. ©1997 American Institute of Physics.