Abstract
This article proposes a novel structure based on vertically folded cascade resonators for the design of a multiband filtering antenna with arbitrary order and arbitrary number of operating bands. A generalized fully coupled theoretical model and the associated systematic synthesis method are established, enabling quantitative analysis and deterministic design of the proposed antenna structure to satisfy the given specifications. By constructing and solving the corresponding multiband low-pass prototype, the theoretical coupling matrix can be derived, which, in turn, guides the physical parameter extraction process of the circuit prototype, greatly simplifying the design and optimization of multiband filtering antennas. The independently tunable cascade modes excited by the cascade resonators allow for precise control over the multiband filtering response, while the vertically folded integrated structure contributes to circuit miniaturization. With the use of substrate-integrated waveguide (SIW) technology, two examples, including second-order dual-band and third-order triband filtering antennas, are designed and fabricated. Good consistency between the simulated and measured results verifies the proposed structure, the theoretical model, and the synthesis method.