Analytical circuit modeling of FSS–plasma structures: Analysis on reflection reduction mechanisms

Plasma integrated with frequency selective surfaces (FSS) has been investigated as a promising approach for reflection reduction, yet the physical mechanisms governing its performance remain insufficiently understood. In this work, an equivalent-circuit model is developed to elucidate the reflection reduction mechanisms in FSS–plasma structures. The model reproduces full-wave electromagnetic simulation results in close agreement, thereby confirming its validity. The validated model was used to analyze reflection reduction behaviors and resonance frequency shifts under both plasma-free and plasma-present conditions. Analysis shows that plasma generation introduces a resistive component to the structure, which achieves reflection reduction by dissipating incident waves through Ohmic losses. The specific frequencies where this reduction occurs are determined by impedance matching, as visualized via Smith chart trajectories. Additionally, the plasma introduction modifies the system's net capacitance, causing a shift in the resonance frequency originally observed in the absence of plasma (the vacuum case). Subsequent parametric analysis clarifies how the resonance frequency varies with plasma frequency, collision frequency, and sheath thickness. This study provides a physical framework for understanding the electromagnetic response of FSS–plasma structures.