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 tu nable diplexer that is being developed as a critical part of a discriminato r-locked tunable oscillator will be discussed. This diplexer consists of tw o K-band (18 to 22 GHz), two-pole YBCO/SrTiO3/LaAlO3 bandpass filters coupl ed to the microwave signal input port through a 50 Omega power splitter. Wh en tested independently at 77 K and varying bias of +/-400 V, these filters exhibited a passband frequency shift greater than 1.7 GHz, while maintaini ng a non-deembeded insertion loss near 2.0 dB, Electromagnetic modeling res ults for the diplexer indicate that varying the dielectric constant of the SrTiO3 from 3000 (similar to 77 K) to 500 (similar to 300 K) will shift the diplexer's "cross-over" frequency from 19 to 21 GHz, with only minor varia tions in insertion loss. Measurements at 298 K of this diplexer circuit usi ng a gold/SrTiO3/LaAlO3 structure resulted in non-deembeded insertion losse s of 3.3 dB and 2.5 dB at the filters' maxima at 20.65 and 22.43 GHz, respe ctively, with a cross-over frequency at 21.07 GHz, These room temperature r esults are consistent with modeling. The measured characteristics of YBCO/S rTiO3/LaAlO3 diplexers at cryogenic temperatures will be presented.