Compact Substrate Integrated Waveguide Bandpass Filters with Wide Stopband

This paper presents two compact wide stopband filters using Complementary Split Ring Resonators (CSRRs) and improved Defected Ground Structure (DGS) based on Substrate Integrated Waveguide (SIW) technology. By loading CSRRs on the top metal layer of the substrate, the resonant frequency can be decreased, thus the size of the filter can be reduced. In order to suppress the high-frequency interference outside the dominant mode, improved Defected Ground Structure is cascaded with the SIW resonator so that the stopband can be widened. Compared to conventional DGS, improved DGS can maintain excellent in-band and out-of-band performance simultaneously. Since the transmission characteristics of the Half Mode SIW are the same as those of the full mode SIW, the size of filters can be further reduced. To validate the method, two compact filters are designed and fabricated, the measured results are in good agreement with the simulated results.