A Compact Quad-band Bandpass Filter Based on Dual-mode Isosceles Right-Angled Triangular Resonator

A quad-band bandpass filter (BPF) based on isosceles right-angled triangular (RAT) resonator is proposed. By combining the two split-type dual-band frequency responses of the first and second resonant modes (LC mode and TM
_100/010
^z
mode) in the isosceles RAT resonator, the filter features compact size. By utilizing the modal bypass couplings and the characteristic of split-type dual-band frequency responses, there are two transmission zeros (TZs) between each passband to improve the out-of-band performance of the filter. Also, the two via-holes connected the patch can control the first two bands independently, making the filter adjustable. The filter is fabricated and measured. The measured results demonstrate the attractive advantages of the designed quad-band BPF. Such as compact size and good performance.