Artificial Magnetic Conductors and High-Impedance Surfaces
Artificial Magnetic Conductors (AMC) and High-Impedance Surfaces (HIS) are easily designed and optimized using the PFSS software tool. Depending on the complexity of the structure and whether or not any vertical vias are included in the design, either the PMM or the PFEBI solver may be used. Depending on the exact structure, one or the other may provide a speed or accuracy advantage.
AMC and HIS are effectively synonymous terms for periodic structures that are designed to be perfectly reflecting at a given wavelength or wavelengths and to provide a reflection phase that is very close to zero degrees, which matches the theoretical boundary condition of a Perfect Magnetic Conductor (PMC). Although this condition may only be matched exactly over an infinitesimally narrow bandwidth, approximately satisfying the condition (reflection phase between ±90°) often yields useful results, and can be achieved over significant bandwidths.
These devices are often used to reduce the vertical profile of planar antennas that are backed by a ground plane. The minimum spacing of antenna to a ground plane affects the efficiency of the antenna – if placed too close, the antenna will suffer reduced gain and high return loss. Replacing a continuous ground plane with an AMC allows the antenna to be placed arbitrarily close to the surface without damaging the radiation characteristics.
Many design strategies for AMC structures exist, including the simple rectangular patch, but different geometries can provide strong benefits. The electrical size of the AMC unit cell must be small in order to support an approximately homogeneous response across the surface. Changing from a square patch to an intertwined or interconnected unit cell can significantly reduce the electrical size of the unit cells and greatly improve the performance of the AMC design, especially when coupling the AMC with an electrically-small planar antenna.
- Bayraktar, Z., J. P. Turpin, and D. H. Werner. “Nature-Inspired Optimization of High-Impedance Metasurfaces with Ultrasmall Interwoven Unit Cells.” Antennas and Wireless Propagation Letters, IEEE 10 (2011): 1563–66. doi:10.1109/LAWP.2011.2178224.