Miniaturized microstrip interlocked-coupled bandpass filters using folded quarter-wavelength resonators

In this paper, the miniaturized microstrip interlocked-coupled bandpass filters are proposed. With the proper utilization of folded quarter-wavelength stepped-impedance resonators, the occupied area of coupled-resonator pair may be reduced. In order to introduce two transmission zeros near the passband, an additional open-stub section is inserted between the low- and high-impedance lines of the resonators to facilitate the generation of cross- coupled path. Making good use of folded quarter-wavelength stepped-impedance resonators, the filters with reduced size and sharp passband selectivity are fabricated and carefully examined. Good agreement between measured and simulated results is observed.