Compact Ultra-Narrowband Superconducting Filter Using Asymmetric Twin-Spiral Resonators

An asymmetric twin-spiral resonator has been proposed to design a compact ultra-narrowband HTS filter. The coupling strength and electromagnetic polarity of the resonator is analyzed. The resonator is possible to reduce the total coupling between adjacent resonators by controlling the amount of electric and magnetic coupling via optimizing the upper and lower length of the resonator structure. Therefore, a weak coupling can be achieved without large spacing. A compact six-pole HTS filter with 0.08% fractional bandwidth at S band is designed and fabricated using the proposed resonator. The measured performance is in a good agreement with our simulation.