Compact UWB BPF using coupled‐line triple‐mode resonator

A novel and compact microstrip ultra‐wideband (UWB) bandpass filter (BPF) based on a triple‐mode resonator is designed, fabricated and measured. The proposed resonator is composed of a coupled line with a half‐pass characteristic, which is connected directly with each other at one end and is short‐circuited to the grounding plane at the other end. A simple structure and design approach to the proposed filter is provided and demonstrated. To implement the design on a microstrip, the directly tapped‐transition input/output ports are used to excite the coupled‐line multi‐mode resonator. The measured results are in good agreement with the electromagnetic simulated results. The proposed filter shows a 3 dB fractional bandwidth of 117.3% at the central frequency ( f c ) with a return loss of better than 12 dB and an insertion loss of < 0.5 dB within the passband response.