Multilayer Cross-Coupled Substrate Integrated Waveguide Filter With Quasi-Elliptic Response and Wide Stopband

Substrate integrated waveguide (SIW) filters usually employ cross-coupling to produce quasi-elliptic responses to achieve steep selectivity near the passband. But the added cross-coupling enables additional transmission of spurious modes and facilitates the generation of spurious passbands, which degrades stopband selectivity and is challenging to address effectively without cascading additional filters or using hybrid resonant structures. This letter proposes a solution. By specially arranging the positions of the coupling structures in a TE₁₀₁ cross-coupled SIW filter, TE₁₀₂ and TE₂₀₁ cannot couple/transmit through both the main and cross-coupling structures. Furthermore, by using a multilayer structure and exchanging the position of the electric coupling, the superior shielding and quality factor of SIW can be maintained. And these operations can be performed without affecting the TE₁₀₁ quasi-elliptic response. As a result, the proposed multilayer cross-coupled SIW filter can effectively achieve a wide stopband in addition to the quasi-elliptic response, and is suitable for integration in high-performance and high-frequency applications. It should be effective for developing SIW filters in wireless and microwave circuits and systems.