Compact and wideband bandpass filters with analysis of the CRLH-TL characteristics based on stepped impedance resonator

Abstract

In this paper, we have investigated two unique wideband (WB) bandpass filters (BPFs) based on composite right/left-handed (CRLH) structure that have high performance in C-band. The proposed filters have been implemented with stepped-impedance resonator (SIR) section and interdigital capacitors on it with a parallel coupled-shorted stub (CSS). High selectivity, high out-of-band rejection, low loss and two transmission zeroes at the lower and upper passband/stopband edges have been observed. The out-of-band rejection levels in two filters are better than 17 dB and 20 dB at the lower and upper band edges, respectively. In addition, the return loss and insertion loss of the proposed CSS filter are greater than 17 dB and less than 0.7 dB, respectively. Also, the return loss and insertion loss of the proposed spiral CSS (SCSS) filter are greater than 20 dB and less than of 0.5 dB, respectively. The presented structures have been investigated analytically and experimentally in order to verify balance between the results of the full-wave simulation and the equivalent circuit model with the experimental ones. The dimensions of the suggested filters are 21.6 × 3.06 mm2 and 14.6 × 4.2 mm2. The specifications and compact size of the filters make them suitable for wideband wireless communication systems.