Cross-coupled band-pass filter using HTS microstrip resonators

We have fabricated microstrip band-pass filters based on the quadruplet geometry using high-temperature superconductor. Every half-wavelength resonator in the filter consists of a loop-like inductor and two patch capacitors at both ends. The inductive coupling in between the loop-like inductors of non-adjacent resonators produces transmission zeros in the frequency response. The transmission zero can be allocated by changing the polarity and the strength of the cross coupling. We have designed a 9-pole filter for personal communication services (PCS) application using combination of a CAD tool and a full-wave analysis EM simulator. We have fabricated filters using double-sided YBa₂Cu₃O_7-δ (YBCO) thin films on LaAlO₃ substrates. The filter has 1.784 GHz center frequency, 11 MHz 3-dB bandwidth, and 0.8 dB insertion loss at 60 K. Due to the transmission zeros near the passband, the steep skirt characteristic is exhibited. The attenuation at 1 MHz away from the edge of the passband is -34 dB