Compact microstrip bandpass filters using miniaturized quarter-wavelength resonators

This paper proposes a novel miniaturized λ/4 microstrip resonator. The two shorted high-impedance lines not only possess the feasibility to be arranged but also provide the strong magnetic coupling between resonators easily. By applying the proposed resonator, the filter with the flexible bandwidth can be realized. Moreover, the spurious frequency can be shifted to the higher frequency by adjusting the structural parameters. The proposed λ/4 resonator has a much smaller size compared to the conventional one. Two four-pole bandpass filters were designed and fabricated to demonstrate the practicality of the proposed resonator. Each filter occupies a small circuit area and has a good stopband response.