A COMPACT QMSIW CSRR BANDPASS FILTER WITH SIMULTANEOUS SIZE REDUCTION AND IMPROVED WIDE STOPBAND

A size-reduced quarter-mode substrate integrated waveguide (QMSIW) band-pass filter (BPF) loaded with combination of complementary split ring resonator (CSRR) and capacitive metal patches is presented. The CSRR generates a passband below the characteristic cutoff frequency of the substrate integrated waveguide (SIW) cavity. Improved stopband rejection is also attainable by loading a capacitive metal patch. Thus, a single-layer compact BPF with wide stopband is realized successfully. The equivalent-circuit model has been derived and analyzed. To verify the validity of the presented method, an experimental filter centered at 2.45 GHz is fabricated and measured. The new filter has the return loss of 16 dB and insertion loss less than 0.9 dB. Out-of-band suppression is better than 20 dB from 3GHz to 11.6 GHz. The whole size of the filter is only 20 × 17.4 × 0.508mm3, achieving 75% size reduction compared to the conventional structure.