Design of miniaturized narrow band filter to consider with cross-coupling effect

We have developed a high-temperature superconducting (HTS) receiving filter with narrow bandwidth characteristic for 2 GHz band mobile communication systems. To reduce the filter size and controlled unintended cross coupling, we proposed a stepped impedance resonator (SIR) and separation filter package. This resonator is possible to control the amount of electric coupling and magnetic coupling by changing the length or width the resonator structure. Therefore, the gap between the adjacent resonators can be achieved more compact size. The developed narrow band HTS filter with a fractional bandwidth of 0.25% has 10-pole quasi-elliptic function response for sharp skirt characteristic. This filter separated two packages to reduce unintended cross coupling, and mounted in the front end systems combining this filter together with low-noise amplifier. The measured frequency response agrees reasonably with the desired specifications.