Highly Selective Planar Microstrip Lowpass Filter Using Interdigital Hairpin Resonator (IHR)

Abstract

Planar microstrip lowpass filter is designed using the inter-digital hairpin resonators (IHR) to achieve high selectivity and suppression is up to 17th order harmonics. The prototype is designed with 3 dB cut-off frequency of 0.82 GHz and obtain rolloff of 185 dB/GHz with 177% relative stopband width. The interdigital effect of cascaded combination of hairpin resonators along with suppressing cells give high end results with normalized cross section of $0.137\ \boldsymbol{\lambda}_{\text{g}}\times 0.069\ \boldsymbol{\lambda}_{\text{g}}$.