A Novel Compact Microstrip Bandstop Filter Based on Spiral Resonators

A novel compact microstrip bandstop filter using spiral resonators (SRs) is proposed. An array of SRs topology which is etched on the center line has stopband characteristics. And this microstrip bandstop filter can be implemented with very small size because of the sub-wavelength effect of SRs. The 3-cell SR filter is fabricated and verified by measurements. We have obtained low insertion loss in the passband and high rejection level in the stopband with steep cutoff. This novel structure is easy to fabricate and is a promising structure that is compatible with MMIC or PCB process.