Negative interresonator coupling structure enclosed in waveguide resonator filter

This work presents a new negative interresonator coupling structure that can be applied to circular waveguide resonators, such as substrate-integrated waveguide (SIW) resonators and metallic cavity resonators utilizing the TM011 mode. The negative coupling is obtained by using the fact that the magnetic field in the resonator circulates in the opposite directions in the upper and lower half parts. As it can be entirely enclosed within a filter structure, it does not produce radiation loss. For verifying the proposed negative coupling structure, we have designed and fabricated a fourth-order bandpsss filter having a pair of transmission zeros using SIW resonators. In addition, the proposed negative coupling structure can be applied to the metallic waveguide cavity resonator filters. Hence, we also have designed, fabricated, and measured a fourth-order metallic cavity bandpass filter having a pair of transmission zeros by adopting the proposed negative coupling structure.