A new family of substrate integrated waveguide metamaterial bandpass filters is proposed which support the backward and forward wave propagations with two adjacent passbands under the cutoff frequency of the structure. Through varying the fractal slots sizes etched overthe SIW structures, different frequency transmission responses were realized. Extraction of the metamaterial parameters was achieved via scattering parameters. The equivalent circuit model was analyzed to provide comprehensionon the SIW-metamaterial unit cells. The equivalent electrical length of a fractal slot is larger than the conventional slot, making it suitable to design highly miniaturized filters. Three filters using the 3rd iteration H-shaped SIW-metamaterial unit cells were designed and testedusing subwavelength resonators. Filter designwas 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 configuring the fractal slots or the SIW. A wide upper out-of-band rejection with attenuation >50 dB with the range 5.5 GHz to 9 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 S21 and S11 were in agreement with the simulated.
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