A compact microstrip wideband bandpass filter with excellent out-band performance

A compact microstrip wideband bandpass filter (BPF) using Stepper-Impedance Resonator with wide stopband is presented. In addition, a input-output cross-coupling was introduced which generated a pairs of attenuation poles at each side of the passband. A wideband microstrip BPF has been designed, fabricated, and measured. The measured filter has a 3 dB fractional bandwidth of 50% with a minimum passband IL of 0.52 dB at 3.71 GHz and a maximum group delay variation of 0.48 ns, respectively. The filter has the advantages of extremely sharp rejection skirts, wide bandwidth, low passband insertion loss (IL), low group delay variation and ease of fabrication.