Compact lowpass filter using spiral compact microstrip resonant cells

A novel lowpass filter using spiral compact microstrip resonant cells (SCMRCs) for size reduction is presented. Four SCMRC resonators as open stub lines are connected at both sides of an SCMRC resonator so that the port impedance at the lowpass band is matched to 50 Ω. The proposed lowpass filter has compact circuit size and wide stop-band. A demonstration lowpass filter is designed, fabricated and measured. It shows low insertion loss, flat response in the lowpass band and wide stop-band.