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| Surface and Volume Moment Method Codes of Antennas |
| Source: Author: Published:1268341545 |
Antennas made of plates or containing finite plate ground planes can be solved by using wire meshing of a thin-wire code. The method of moment code has been extended to plates using a rooftop basis function on both rectangular and triangular patches. The number of basis functions (i.e., matrix size) grows rapidly. One solution is to use entire domain basis functions. These require more complicated integrals, but they reduce the matrix size. Dielectric portions of the problem lead to either volumetric integrals or various forms of surface integrals that use equivalent currents to replace the internal fields. These problems lead to a variety of boundary conditions solved using a finite series of basis function and integral equations to satisfy those boundary conditions approximately.
MOM analysis of antennas mounted on dielectric substrates requires special techniques. Commercial codes determine the currents flowing on these antennas while accounting for the dielectric. Often, Green’s functions are found numerically, which increases the execution time. Since the currents are located on the surface and the integrals of the boundary conditions are over the same surface, the singularity of the Green’s function causes a numerical problem. For example, the free-space Green’s function has the term 1/|r – r’|, which becomes infinite on the surface. Spectral domain methods remove the singularity by using a sum of current sheets on the surface as an entire domain basis function. A uniform plane wave propagating at an angle to the surface excites the current sheet. The actual current flowing on the metal portions is expanded as a sum of these current sheets. The uniform current sheets are expanded in a spatial Fourier transform as well as the Green’s function, and the MOM problem is solved. The Fourier-transformed Green’s function no longer has the singularity. When the metallization can be expressed as an infinite periodic structure, the current is expanded as a Fourier series. The infinite periodic structure is used with frequency-selective surfaces and infinite arrays. In this case the fields and currents are expanded in Floquet modes (harmonics). |
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