Ultra-narrow band tunable superconducting filter with constant bandwidth and same transmission zero points

We have proposed an ultra-narrow band tunable superconducting filter with constant bandwidth and same transmission zero points for X-band RF applications. This tunable filter tuned center frequency by dielectric rods with actuator. At the same time, coupling coefficients and external Q of the filter change with individual gradient. This filter realized constant bandwidth and same transmission zero points by means of position at coupling microstrip line. The developed tunable superconducting filter has 4-pole elliptic function response for sharp skirt characteristic. Tuning range was between 9700 MHz and 9800 MHz for weather radar. Also, this filter had fractional bandwidth of 0.04%.