Dual-band HTS filter using modified dual-spiral resonators

A symmetric dual-band filter with a centre frequency of 887MHz is presented. The filter uses a modified structure of dual spiral resonators with interdigital capacitive load. At the same resonant frequency, the resonator can occupy an area of less than 2.75 of the area of the square loop resonator. Moreover, the resonator has a very low sensitivity to substrate thickness. The resonator structure also allows two types of couplings and, hence, allows application of cross-couplings with different signs to the direct couplings.