D-Band E-Plane Waveguide Bandpass Filters Using Spoof Surface Plasmon Polaritons and Slotted Metal Diaphragms

In this article, a new design method for D-band E-plane waveguide bandpass filters (BPFs) based on the spoof surface plasmon polaritons (SSPPs) and slotted metal diaphragms (SMDs) is proposed, which is analyzed by the slow wave theory of periodic structure. The SSPP structure is fabricated by the electrical discharge machining (EDM) process, which is etched on the copper foil and inserted into the E-plane of the rectangular waveguide (RWG). Due to the introduction of parallel equivalent capacitors in the symmetric slotted structure, the bandpass filtering response can be realized by the SSPP itself. For validation, two different types of D-band E-plane SSPP waveguide BPFs are presented by using slow wave theory and electromagnetic (EM) simulations. The simulated results show that the center frequency and bandwidth of the BPFs can be flexibly tuned by adjusting the size of the SSPP unit cell. To demonstrate and verify the design feasibility, two types of BPFs are fabricated and measured. Good agreement between measured and simulated results shows that the proposed idea will be a good candidate for the D-band waveguide BPF design with compact size, low insertion loss, and flexible tuning ability.