E-plane waveguide bandpass filters based on high-order modes of spoof surface plasmon polaritons

In this paper, a new design method of E-plane waveguide bandpass filter (BPF) using high-order modes of spoof surface plasmon polaritons (SSPPs) is proposed. The high-order modes of the double-layer SSPP (DL-SSPP) unit cell can be effectively manipulated by adjusting the dimensions of grounded metallic patterns in SSPP array, which mainly determines the filtering characteristics of E-plane waveguide BPFs. For improving the out-of-band rejection, two extra transmission zeros (TZs) are designed at the upper and lower stopbands of E-plane waveguide BPF, and then the operating mechanism of TZs is clearly investigated. Moreover, the filtering characteristics of the E-plane waveguide BPF with different transition parts are discussed to demonstrate the generalization of proposed design method. To verify the design feasibility, two examples of E-plane waveguide BPF are fabricated and measured. Good agreement between measurements and simulations shows that the proposed design method possesses good potential for the applications of high-performance E-plane waveguide BPF design.