Compact Multilayer SIW Bandpass Filter With Cross Coupling and Source-to-Multiresonator Coupling

In this article, a compact high-selectivity multilayer substrate integrated waveguide (SIW) filter bound by prepreg is proposed. The filter employs two quarter-mode SIW (QMSIW) cavities in the upper layers and a full-mode SIW cavity in the lower layers. By integrating the prepreg into the cavity, the filter can be mounted directly without screws, providing better integration for high-frequency filters and preventing the introduction of spurious signals by prepreg near the passband. The utilizing of QMSIW cavities can simultaneously introduce the cross coupling and source-to-multiresonator coupling, realizing a pair of transmission zeros (TZs) in the third-order filter. Additionally, it circumvents the design limitations of non-through vias imposed by printed circuit board (PCB) layout punching requirements. The measured center frequency of the filter is 24.64 GHz, with a minimum insertion loss of 1.20 dB and a return loss better than 16.70 dB. A pair of independent controllable TZs are located at 22.27 and 27.87 GHz, respectively. The proposed filter exhibits high selectivity, compactness, improved integration, and ease of manufacturing.