Scattering Calculation and EMI/EMC Modeling Computer Programs for Antenna Design

1. Enhanced NEC Code.

This program is designed to code ENNEC speed up the NEC code and to increase its range of applicability. It does this by replacing certain portions of the NEC code with modules that can solve the matrix generated by NEC much more rapidly. Other refinements of the program are also included.

2. Scattering by a PEC Body with Arbitrary Wire Attachments

This program is designed to calculate the current distribution on an arbitrarily- shaped conducting body, with arbitrary wire attachments, using an integral equation approach. The knowledge of the current distribution is used next to compute the monostatic or bistatic RCS of the scatterer. The program is also useful for calculating the radiation pattern of an antenna mounted on a conducting body, and for investigating the compatibility problem between two antennas.

The program utilizes a patch-type description of the body and achieves a more accurate description of the scatterer than would be possible with a wire-grid model. It can be linked to an automatic mesh generating program, e.g., PATRAN, to model arbitrary surfaces. The program can also handle impedance type surfaces. We also have a generalized version of the program that handles scatterers with lossy dielectric or magnetic coatings.

3. Scattering by a PEC Body of Revolution Coated with One or More Layers of Dielectric or Magnetic Material

This program calculates the surface electric and magnetic currents on the different layers of coating of a perfectly conducting body of revolution (BOR) of an arbitrary shape. The BOR may be large compared to the wavelength of the incident field which may impinge on the scatterer at an arbitrary angle with respect to the axis of the BOR. The output of the program is the monostatic or bistatic RCS of the scatterer for both the incident polarizations.

4. Finite Element Solution of Arbitrary Three-dimensional Structures Using Edge Elements for Frequency and Time Domain Solution

This is a general-purpose three-dimensional program for time and/or frequency domain solution of scattering problems using unstructured grids. It has better accuracy than some of the other unstructured grid programs, it is accurate because it is based upon the Galerkin formulation, and, in addition, it is unconditionally stable. The latter feature is not available in several formulations that employ non-orthogonal grids, and exhibit long-term instability.

5. Finite Element Solution of Scattering by Periodic Structure

This is also a general-purpose FEM code for solving the problem of scattering from doubly-periodic structures that can have arbitrarily inhomogeneous elements.

6. Scattering by Frequency Selective Surfaces

This program is designed to compute the frequency response of a single screen comprising of periodic, conducting patches, or apertures in conducting planes. The screen may be residing on a substrate and be covered by a superstrate whose dielectric constants may be arbitrary. The incident field can have an arbitrary polarization and be incident from an arbitrary angle. Both the in-band and out-of-band response of the screen can be computed. The program is general enough to handle dielectric and conducting losses and is also generalizable to the case of screens loaded with lumped elements.

The program can handle arbitrary element shapes. It is numerically efficient, as it employs a special summation technique for generating the matrix elements. It is capable of dealing with situations where a large number of unknowns are needed. It has been thoroughly tested for accuracy. It is useful as a design tool.

7. Scattering from Multiple Screens Separated by One or More Dielectric Layers

Multiple screens are often employed in the design of radomes in order to achieve a desired frequency characteristics. This program has been designed to compute the frequency response of a multiple-screen FSS separated by arbitrary dielectric layers. The program uses a cascading approach to derive the scattering properties of multiple screens from the knowledge of the scattering matrices of the individual screens. The scattering matrix of individual screens are computed by using the program FSS1 described in the last paragraph.

The program handles arbitrary number of screens and dielectric layers. The screens may have different element shapes. However, the period is assumed to be the same for all screens.

8. Synthesis of FSSs using the Genetic Algorithm

This program utilizes the Genetic algorithm to synthesize single or multi-layered FSSs to achieve a prescribed frequency response.

9. Conformal Finite Difference Time Domain Code

This is an FDTD code for solving the field problem in an region filled with inhomogeneous objects. Several different versions of this code are available. They include:

(1) Uniform Cartesian grid version with MUR boundary condition;

(2) Non -uniform version with error correction;

(3) PML mesh truncation;

(4) Circulaly-symmetric version;

(5) Doubly-periodic periodic version.

Hybrid codes, e.g., FDTD/FVTD and FDTD/MoM are under development.

10. Design of Broadband (15:1 or greater Bandwidth and multiband Antennas) Using the Genetic Algorithm and Fractal Concept

This program uses the newly-developed genetic algorithm, which is an optimization scheme, for systematically designing broadband antennas that may be mounted on complex structures. It also employs the Fractal and modified fractal approaches for synthesizing multiband antennas.