In this letter, a compact, fully uniplanar bandstop filter is presented. It is based on multimodal coplanar waveguide resonators implemented using a slow-wave periodic structure that greatly reduces the filter’s horizontal dimension. A multimodal circuit model for the filter is proposed and experimentally validated. A second-order filter prototype at 1.9 GHz, with a compact size of 0.31¿g×0.19¿g , was designed and fabricated. The filter features measured fractional bandwidths of 9.3% and 3.7% for -20- and -30-dB rejection levels, respectively, and a 1.3-dB insertion loss in the passband.

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