High impedance surfaces

High impedance surfaces are thin resonant cavities synthesized by printing a periodic frequency selective surface (FSS) on the top of a grounded dielectric slab. As is well known, these structures mimic the perfect magnetic conductor (PMC) condition within a fixed frequency range and, for this reason, they are often referred to as artificial magnetic conductor (AMC) [1,2]. The use of these surfaces is relevant in microwaves area mainly in the design of ultra-thin electromagnetic absorbers, low-profile antennas, Fabry-Perot or Leaky wave antennas, to mitigate the simultaneous switching noise (SSN) in PCB circuit and other applications.

In [3] it is shown that the conventional approach describing the high-impedance surface as a parallel connection between the inductance given by the grounded dielectric substrate and the capacitance of the FSS induce to inaccurate results in the determination of the operating bandwidth of the structure since because of the absence of the series FSS inductance. An explicit expression for defining the bandwidth of a high-impedance surface (HIS) is derived and it is shown that the minimization of the FSS inductance (high capacitive elements) results the best choice for achieving wide operating bandwidth in correspondence of a given frequency.

The high-impedance surface can be transformed into an active structure by connecting a couple of varactors to each unit cell of the FSS [4].