Mushroom-Type High-Impedance Surface With Loaded Vias: Homogenization Model and Ultra-Thin Design

In this letter, we study the reflection properties and natural modes (surface waves and leaky waves) of the mushroom-type surfaces with impedance loadings (as lumped loads) at the connection of the vias to the ground plane. The analysis is carried out using the nonlocal homogenization model for the mushroom structure with a generalized additional boundary condition for loaded vias. It is observed that the reflection characteristics obtained with the homogenization model strongly depend on the type of the load (inductive or capacitive) and are in a very good agreement with the full-wave simulation results. The proposed concept of lumped loads enables the design of an ultrathin mushroom-type surface with high-impedance resonance characteristics (zero reflection phase) for oblique incidence at low frequencies with a broad stopband for surface waves.