Segmentation strategy for the efficient analysis and design of substrate integrated waveguide directly coupled cavity filters

In this study, a new segmentation strategy is presented for the full-wave analysis of directly coupled cavity filters in substrate integrated waveguide (SIW) technology. The whole SIW filter is enclosed inside an external fictitious rectangular waveguide, which does not affect the propagation inside the SIW assuming that the SIW is well designed and there is no significant power leakage. The external rectangular waveguide allows to easily segment the structure into building blocks that are composed of circular metallic vias inside a rectangular waveguide. The generalised scattering matrix of these building blocks is obtained with highly efficient techniques specifically suited for the analysis of H-plane rectangular waveguide devices. Some building blocks are repeated along the structure, and their scattering matrix has to be computed only once. The scattering matrices of all the building blocks are cascaded and the scattering matrix of the whole filter is obtained. A SIW filter of eight coupled cavities with a bandpass response centred at 11 GHz is analysed. Results from this analysis show that the computational time has been significantly reduced when compared with other specific SIW analysis methods or with commercial general purpose software, while maintaining a good accuracy.