Compact transition enabled broadband propagation of spoof surface plasmon polaritons based on the equivalent circuit model

Abstract

In this paper, a strategy to develop a compact transition of the spoof surface plasmon polariton (SSPP) transmission line (TL) is proposed. First, an equivalent distributed circuit model is employed for the theoretical analysis and optimization design of the SSPP unit. The mapping relation between the unit performance and the geometric parameters is deduced from the transmission matrix. The calculated results are compared with the numerical ones from the three-dimensional (3D) simulations for validation. Then, a compact transition (only 0.26λ g) is built with only two matching units and a tapered strip through optimizations. The optimizations are implemented with the circuit simulations based on the equivalent model, which can remarkably save time in comparison with the 3D simulations. The transition principle is also explained by quantitatively extracting the dispersion properties and impedance characteristics. Finally, a prototype of the proposed SSPP TL is fabricated and measured for demonstration. The measured operating band (0–7.7 GHz) is almost up to the cut-off frequency (about 8 GHz), which remains the inherent broadband low-pass transmission characteristics. Meanwhile, the measured in-band return loss is almost higher than 10 dB, which verifies the high-efficiency propagation. This work can pave the way for building up a new SSPP-based framework of microwave circuits.