Substrate integrated waveguide bandpass filter with novel cascaded complementary electric-LC resonators

In this paper, a substrate integrated waveguide (SIW) bandpass filter based on the novel cascaded complementary electric-LC (CCELC) resonator is presented. The unit cell of the SIW with the complementary electric-LC (CELC) resonator is investigated first. It is shown that the SIW with the CELC resonator exhibits a better filtering response and an improved out-of-band performance in comparison to the SIW with the conventional CSRR. By combining two CELC resonators together, a novel cascaded CELC (CCELC) resonator is then proposed to further improve the stopband rejection. A second order SIW bandpass filter with the CCELC resonator is designed and fabricated. Good agreement is achieved between the measurement and the simulation. The proposed SIW bandpass filter with the CCELC resonator shows a very sharp upper transition band and a broad rejection band, and it is low loss, low cost, easy to fabricate and integrate with other microwave circuits.