A dual-band filter based on blind-vias-patterned eighth-mode substrate integrated waveguide with L-shaped microstrip line

This paper reports a dual-band filter using eighth-mode substrate integrated waveguide (EMSIW) and microstrip line. By patterning blind vias periodically in the conventional EMSIW cavity, the equivalent capacitance of the structure can be enlarged, thus its resonant frequency will be effectively decreased. Then, as a L-shaped microstrip line is connected with the blind-vias-patterned EMSIW, dual-mode resonance is generated and two individual passbands can be achieved. By using the EMSIW-microstrip dual-mode resonator, a dual-band filter is designed and optimized. Numerical simulations show that the dual-band filter achieve two passbands of 1.58-1.68GHz and 2.55-2.85GHz. The insertion losses are less than 2.1dB and 1.2dB, respectively, with the return losses both better than 16dB. The out-of-band rejection between the two passbands is over 16dB.