A Ultra Compact Wideband Bandpass Filter Using a Quadmode Stub-Loaded Resonator

An ultra compact microstrip wideband bandpass filter (BPF) using a quadmode stubloaded resonator is presented in this letter. The resonant characteristics of the quadmode resonator are explored by adopting odd- and even-mode analysis. The four resonant frequencies of this resonator can be controlled independently. For demonstration purpose, a wideband BPF is designed, fabricated and measured. The measured results are in good agreement with the full-wave simulation results. The realized wideband filter exhibits a 3 dB fractional bandwidth (FBW) of 45% with good in-band filtering performance and sharp out-of-band rejection skirt.