High Selectivity Bandpass Filter Using Substrate Integrated Waveguide Technique

In this paper, a compact filter with high performance and wideband harmonic suppression using substrate integrated waveguide technique is proposed. The filter is designed by square complementary split-ring resonators (CSRRs) and short-circuit centered stepped impedance resonators (SCSIRs). High selectivity and wideband harmonic suppression are achieved by controlling the transmission zeros. The center frequency and transmission zeros near the passband can be controlled independently by adjusting the parameters of the CSRR and the SCSIR, respectively. A bandpass filter is designed with the typical coupling matrix theory. The measured insertion loss is within 2 dB for the filter. The transition band from the cut-off frequency to 40 dB attenuation is only 0.12 GHz.