A novel super compact half-mode substrate-integrated waveguide filter using modified complementary split-ring resonator

A novel super compact filter based on half-mode substrate-integrated waveguide (HMSIW) technology loaded by the modified complementary split-ring resonator (MCSRR) is proposed. The working principle of the proposed filter is based on the evanescent-mode propagation technique. According to this technique, by loading the complementary split-ring resonator (CSRR) on the metal surface of the substrate-integrated waveguide (SIW) structure, an additional passband below the SIW cutoff frequency can be obtained. In order to miniaturize the physical size of the conventional CSRR, a new method is introduced. In the proposed MCSRR unit-cell, the meander slots are carved inside all of the interior space of the ring. Accordingly, the length of the slot is increased which leads to an increase in the inductor and capacitor of the proposed structure without occupying the extra space. Therefore, the electrical size of the proposed MCSRR unit-cell is reduced. Consequently, the resonance frequency of the proposed MCSRR unit-cell is decreased compared to the conventional CSRR with the same sizes. Namely, the lower resonance frequencies can be achieved by using this technique without increasing the size of the unit-cell. In order to confirm the miniaturization technique, two HMSIW filters loaded by the proposed MCSRR unit-cell are designed, fabricated, and experimental verifications are provided. The results show that a miniaturization about 67% is achieved.