A wideband bandpass filter with compact size and good selectivity

This paper presents a microstrip wideband bandpass filter (WBPF) with high selectivity and compact size. The proposed WBPF consists of quarter-wavelength microstrip coupled three-line sections with grounding via. Due to the strong coupling between the coupled-lines, a tri-mode bandpass responses could be realized. In addition, two grounding vias are attached to the coupled lines to generate multiple transmission zeros to improve the selectivity of the proposed filter, and the proposed filter demonstrates quasi-elliptic function wideband bandpass response. Finally, the proposed filter is implemented and fabricated for measurement, and the measured results match the analytical ones very well.