Compact Dual-Mode Bandpass Filters Based on Half-Mode Substrate Integrated Waveguide Cavities

This letter presents a novel class of compact dual-mode bandpass filters based on half-mode substrate integrated waveguide (HMSIW) cavities. By using both TE102 and TE301 modes of the HMSIW rectangular cavity as resonant modes and TE101 mode as non-resonating mode, a novel HMSIW doublet with two poles and two transmission zeros (TZs) is implemented. The TZs can be located at one side or both sides of the passband. Therefore, flexible responses can be obtained. A two-pole HMSIW filter with asymmetric response and a four-pole HMSIW filter with quasi-elliptic response have been designed, fabricated and measured, to demonstrate and verify the proposed structure. Compared with SIW counterparts, the dual-mode HMSIW filters have the advantage of smaller size.