New Negative Coupling Structure for ${K}$ -Band Substrate-Integrated Waveguide Resonator Filter With a Pair of Transmission Zeros

In this letter, we present a new negative coupling structure applicable to a substrate-integrated waveguide (SIW) resonator filter structure. Unlike conventional negative coupling structure, the proposed coupling structure can achieve a negative coupling value without employing an additional substrate or slots on ground planes. To demonstrate the new negative coupling structure, we designed, fabricated, and measured a fourth-order K-band SIW resonator filter with a pair of transmission zeros.