A General Method for Implementing Flexible Filter Design Based on Nested Substrate Integrated Waveguide Circular Cavity and Cambered Cavity

In this article, a general method for implementing flexible filter design based on nested substrate integrated waveguide (SIW) circular cavity and cambered cavity is proposed. The unique physical structure of the cambered cavity allows for additional coupling between two nonadjacent resonators, resulting in additional transmission paths and cross-coupling in addition to the conventional main coupling. Furthermore, the cambered cavity can be divided into any angle to increase the topology order, which enables a more flexible topology and the implementation of various types of filters. Based on the electric field distribution characteristics and the difference in the frequency distribution of higher order resonant modes between the cambered cavity and the circular cavity, single-band bandpass filters (BPFs) with wide stopband can be implemented. In addition, dual-band BPFs and triple-band BPFs with different frequency ratios can be achieved by introducing additional transmission paths between cambered cavities. Filtering power dividers (FPDs) with controllable transmission zeros (TZs) can be realized by utilizing the cross-coupling phenomenon between the cambered cavity and the circular cavity. All of the designs are constructed, fabricated, and measured at 25 GHz to demonstrate their feasibility and universality. The measured results are in good agreement with the synthesized and simulated counterparts.