Defected ground structure band-stop filter by semicomplementary split ring resonators

This study proposes a band-stop filter using a defected ground structure. The notch frequency is produced by an array of two semicomplementary split ring resonators (SCSRRs), etched on the ground plane and two line resonators etched out of the microstrip line. Band reject behaviour is exhibited due to the presence of a negative effective dielectric permittivity near the resonance frequency. The filter produces high rejection with sharp cutoffs in the stop band, and shows a completely flat and lossless passband. In addition, because of the geometrical structure of the resonators and the filter, even harmonics responses of the filter are eliminated. The proposed filter is constructed on a substrate with a thickness of 0.8128 mm, ε_r of 3.55 and dimensions of 30 × 45 mm². Measurements show an insertion loss below 30 dB from 2.3 to 2.7 GHz and a maximum insertion loss of 44 dB at around 2.53 GHz. The electrical size of the filter is small due to the sublambda operation of SCSRRs and is verified in the last section by comparing the proposed filter with other familiar metamaterials such as complementary split ring resonator. Moreover, the distributed equivalent circuit model based on geometrical filter parameters is introduced.