A K-band (HTS,gold)/ferroelectric thin film/dielectric diplexer for a discriminator-locked tunable oscillator

The performance of a K-band conductor/ferroelectric thin film/dielectric tunable diplexer that is being developed as a critical part of a discriminator-locked tunable oscillator will be discussed. This diplexer consists of two K-band (18 to 22 GHz), two-pole YBCO/SrTiO/sub 3//LaAlO/sub 3/ bandpass filters coupled to the microwave signal input port through a 50 /spl Omega/ power splitter. When tested independently at 77 K and varying bias of /spl plusmn/400 V, these filters exhibited a passband frequency shift greater than 1.7 GHz, while maintaining a non-deembedded insertion loss near 2.0 dB. Electromagnetic modeling results for the diplexer indicate that varying the dielectric constant of the SrTiO/sub 3/ from 3000 (/spl sim/77 K) to 500 (/spl sim/300 K) will shift the diplexer's "cross-over" frequency from 19 to 21 GHz, with only minor variations in insertion loss. Measurements at 298 K of this diplexer circuit using a gold/SrTiO/sub 3// LaAlO/sub 3/ structure resulted in non-deembedded insertion losses of 3.3 dB and 2.5 dB at the filters' maxima at 20.65 and 22.43 GHz, respectively, with a cross-over frequency at 21.07 GHz. These room temperature results are consistent with modeling. The measured characteristics of YBCO/SrTiO/sub 3//LaAlO/sub 3/ diplexers at cryogenic temperatures will be presented.