H-SHAPED FRACTAL SLOTS BASED HIGHLY MINIATURIZED SUBSTRATE INTEGRATED WAVEGUIDE METAMATERIAL BANDPASS FILTERS FOR C-BAND APPLICATIONS

A new family of substrate integrated waveguide SIW-metamaterial bandpass filters is proposed which support backward and forward wave propagations with two adjacent passbands under the cutoff frequency of the conventional SIW structure. Through varying the fractal slots sizes etched over SIW structures, different frequency transmission responses were realized. Extraction of the metamaterial parameters was achieved via scattering parameters. The equivalent electrical length of a fractal slot is larger than the conventional slot, making it suitable to design highly miniaturized filters. The equivalent circuit model was analyzed in detail to provide comprehension on the SIW-metamaterial unit cells. Three filters using the 3rd iteration H-shaped SIW-metamaterial unit cells were designed and tested using subwavelength resonators. Filter design was used to extract the coupling coefficient and external quality factor to obtain the filters' optimized physical dimensions. The out-of-band rejection can be enhanced by reconfiguring the fractal slots or the SIW. A wide upper out-of-band rejection with attenuation > 30 dB with the range 5.5 GHz to 8 GHz was realized. The proposed filters offer advantages through low insertion loss, easy fabrication, high selectivity, small size, and low cost. The measured scattering parameters [S.sub.21] and [S.sub.11] were in good agreement with the simulated ones.