Design and Fabrication of Compact Waveguide Filter with Complementary Split-ring Resonators (CSRR)

To achieve new properties or to improve current characteristics of filters various complex metal-dielectric inhomogeneities are used in waveguide structures. As known thin irises with different transverse cross sections across the waveguide may serve as inhomogeneities. The classical rectangular resonant irises have a rather low Q-factor. So it is difficult to design narrow-band filters. To increase the Q-factor of the resonant irises it is possible to use a resonant window with more complex cross-section. In our research compact narrowband band pass waveguide filter on rectangular waveguide with combination of complementary split ring resonators (CSRR) and Koch fractal are developed. The proposed filter has been simulated using CST Microwave Studio. An electrodynamic analysis of single resonant diaphragms are presented in the research. The investigation of resonance frequency on geometric parameters of structure are shown. The obtained results of single iris are used to synthesize a band-pass filter of the third order. The developed filter is manufactured on a WR137 rectangular waveguide. The comparison of amplitude frequency response of computer model and manufactured filter are presented. Resonant diaphragms are made by applying metallization to a dielectric plate 1.5 mm thick. The longitudinal dimension of manufactured band-pass filter is only 35 mm. The passband at the 3 dB level is $6.71 \div 7.79$ GHz or 14.93%. The bandwidth shape factor of a filter at 3 and 20 dB levels is 0.65. It shows that the developed filter has a high selectivity. The obtained results of investigated structure can be used to achieve more compact and light weight waveguide filters..