Design of an Inductive Spiral-Loop Loaded Unit Cell in a Mushroom-Shaped High Impedance Surface for Sub-GHz Applications

A high impedance surface has far-reaching potential in wireless applications, but realization of the surface operating at sub-GHz ranges is challenging due to its size limits in practical applications. Here, we present a novel inductive technique based on multi-turn square spiral loops. The introduction of the spiral loops to a mushroom-shaped high impedance surface provides additional current path, thereby results in a dramatic increase in its total inductance at given dimensions, and therefore leads to a significant reduction in a resonant frequency of a high impedance plane. Electromagnetic simulation results reveal that a resonant frequency shifts downward 1 GHz at a given dimension, and they are in good agreement with results from an analytical model for the proposed structure. Experimental measurements suggest the feasibility of the proposed approach.