A resistor-loaded microstrip line resonator with a punched hole structure for ultra-wide-stopband bandpass filters

A novel microstrip line resonator is proposed for ultra-wide-stopband microwave bandpass filters. It consists of a stepped-impedance resonator (SIR) with a high-impedance transmission line on punched hole structure (PHS), and thin-film resistors implemented in the SIR for absorbing higher-order resonance power. A fabricated 2-stage microstrip bandpass filter at f
₀
= 2.0 GHz has realized a spurious response level <; -29 dB up to 25 f
₀
, which seems to be the superior wide-stopband performance among ever-reported ones in the category of microwave microstrip line filters.