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EM Modeling of Artificial Magnetic Conductors and Soft and Hard Surfaces
The 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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