A high-temperature superconducting bandpass filter with microstrip quarter-wavelength spiral resonators

A high-temperature superconducting bandpass filter at 408 MHz using microstrip quarter-wavelength spiral resonators is demonstrated. The quarter-wavelength spiral resonators were shorted to ground, as in a combline filter, via a grounding strip that is attached to the box wall by a number of aluminum bonding wires. The introduction of the normal metal wires does not introduce a measurable attenuation. The filter achieves a symmetrical quasi-elliptic characteristic by using two cross-coupling links. The experimental results of the filter are in very good agreement with the simulated ones.