MULTIPLE MULTIPOLE PROGRAM COMPUTATION OF PERIODIC STRUCTURES

The three-dimensional multiple multipole program (MMP) code based on t he generalized multipole technique is outlined for readers who are not familiar with its concepts. This code was originally designed for com putational electromagnetics. Rayleigh expansions and periodic boundary conditions are two new features that make MMP computations of arbitra ry periodic structures efficient and that at the same time allow us to take advantage of the benefits of other MMP features, including surfa ce impedance boundary conditions and a variety of available basis func tions for modeling the electromagnetic field. The application of three -dimensional MMP to a simple grating of highly conducting wires with r ectangular cross sections illustrates the high accuracy and the fast c onvergence of the method as well as the use of surface impedance bound ary conditions. A more complicated biperiodic array of helical antenna s demonstrates the application of thin-wire expansions in conjunction with regular MMP expansions. This model can be considered a simulation of a thin, anisotropic chiral slab with interesting characteristics.