Incorporation of CSRRs for Bandwidth Enhancement of SIW Bandpass Filter

This paper deals with the incorporation of complimentary split ring resonators (CSRRs) for enhancing bandwidth of SIW bandpass filter. The proposed filter which is designed and deployed on a 1.524mm thick Rogers 4003C dielectric substrate is intended to operate at the center frequency of 3.5 GHz. In order to attain the filter with a wide bandwidth response, an array of 14 CSRRs is incorporated on the SIW surface and arranged in a certain configuration to improve the mutual coupling. The incorporation of CSRR is also utilized to enhance the filter performance in gaining the reflection coefficient value. Based on the optimum design result, the configuration of SIW bandpass filter with CSRR incorporation is then fabricated and experimentally characterized. The measurement result shows that the realized SIW bandpass filter with CSRRs incorporation works at the center frequency of 3.38 GHz with the bandwidth of 1.24 GHz, or the fractional bandwidth $(f_{\text{BW}})$ of 36.7%. This achievement is wider than the conventional one which has the second center frequency of 4.29 GHz with the bandwidth of 0.48 GHz, or $f_{\text{BW}}$ of 11.2%. In addition, loading CSRRs into SIW bandpass filter can improve the reflection coefficient value more than 5 dB at its passband frequency range.