EM Modeling of Artificial Magnetic
Conductors and Soft and Hard
SurfacesThe term soft and hard surfaces is recently used with
surfaces based on the direction of propagation along the surface. Soft surfaces
are long been used in horn antennas as transverse corrugations to improve the
radiation characteristics. A grounded
dielectric slab loaded with transverse metallic strips can realize also soft
surfaces. Longitudinal corrugations or
longitudinal strips can realize hard surfaces. Such surfaces have recently
found some applications and relation with the electromagnetic band gap surfaces
(EBG) and artificially magnetic conducting surfaces (AMC). The analysis of
these surfaces using exact boundary conditions is tedious and sometimes is
limited to certain geometrical constraint when periodicity has to be analyzed
using Floquet modes. Recently, simplified boundary conditions have
been developed to analyze such surfaces. Such boundary conditions remove the
geometrical restrictions and able the analysis of complex surfaces with
different types. These asymptotic boundary conditions are used under the
condition that the structure period is very small compared to the wavelength
and ideally when the period approaches zero. Three types of asymptotic boundary
conditions are considered. The
asymptotic strips boundary conditions (ASBC) to be used with strips loaded
surfaces. The asymptotic corrugations boundary conditions (ACBC) to be used
with corrugated surfaces. The third type can be used with strips or
corrugations under the assumption of ideal soft or hard conditions. The surfaces can be model as periodic surface
of perfect electric conducting strip (PEC) attached to a perfect magnetic
conducting strip (PMC). This boundary
condition is referred to as PEC/PMC surface.
Also, the classical model of surface impedance boundary condition can be
used with some of these surfaces. A review related to these boundary conditions
will be given. We will show the implementation of these boundary conditions in
method of moments (MoM) based on surface integral equations and the finite
difference time domain method (FDTD).
The advantages of using the asymptotic boundary conditions will be
illustrated. The relation between the soft surfaces and the electromagnetic
band gap (EBG) surfaces will be discussed. We will present several examples of
applications such as compact horn antennas with soft or hard surfaces,
reduction of blockage from cylindrical objects and others applications.
A
newly developed guiding structure will be presented, which is based on the
properties of the AMC with low loss. Also, a demonstration of using AMC in
packaging microwave circuits will be presented. |

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