Half mode substrate integrated waveguide (HMSIW) notch filters using open ring resonators

An open ring resonator (ORR) is applied to a half mode substrate integrated waveguide (HMSIW) for the design of notch filters. This ORR cell is connected in parallel with a HMSIW section. The measured ORR-loaded HMSIW has the same behavior as a shunt series LC resonant circuit with a 3 dB stop-band bandwidth lower than 5 % and insertion loss above 15 dB. This ORR cell can be useful for the design of higher-order band-stop filters and reconfigurable HMSIW band-stop filters by placing a varactor diode connected to the open ring resonator.