IF antenna id = 100 ( Spiral ), data will take on the following order

ELSE, data will take on the following order

IF antenna id is not equal to 1 (Antenna type is not Electric Monopole), then

width and orientation will also be read in IF
antenna id = 2 (Magnetic rectangular aperture (slot) with uniform curren)
antenna id = 3 ( Magnetic rectangular aperture (slot) TE01 mode type)

Coordinate Systems

The model, location of antenna, and generated paths are defined in terms of thee Cartesian Coordinates X Y Z.

The pattern is defined by ELEVATION and AZIMUTH that are related to the usual sherical angles PHI and THETA as described in the illustration below:

Platform Model

Typically, aircraft or other platform models are created by computer aided design (CAD) software systems which let the user output a representation of the model in some electronic format, usually, specific for the utilized CAD system. In order to exchange information between different CAD systems, various translators/converters have been developed. Such translators are supposed to make a representation developed by one system readable by another system. However, such a translation/conversion can be a very complex process and certain information in this process may be lost or distorted. Consequently, as a general rule, it is a good practice to examine the model for consistency and absence of defects. In order to make this task easier for the DOVA user, we identified several very basic requirements that models intended to be analyzed with DOVA should satisfy.

Target Model Requirements

The following list, broken into two groups, describes these requirements.

The first group consists of requirements that must be satisfied in order for DOVA to begin and complete execution of all computational procedures. These requirements are as follows:

1. The aircraft surface should consist of planar triangular facets (triangles).
2. Any pair of surface triangles should either have no points in common, or have only one common edge, or a common vertex. Overlaps are not allowed.
3. Each edge of a surface triangle should be shared by exactly two triangles.
4. The aircraft surface must be connected, that is, on such surface it should be possible to connect any two points with a continuous curve lying completely on the surface.
5. The aircraft surface is oriented by the outward normal.
6. Interior parts, such as chairs, internal walls, devices, etc. should be removed.
7. Engine inlets should be closed.
 
The second group includes the requirements 8 and 9 below. These are the requirements under which performance of DOVA is expected to be most efficient in terms of speed and robustness. They have been developed experimentally, primarily, by testing various components of DOVA on SGI computers and PC workstations, and from our experience with other software packages that perform geometric calculations.
 
8. Let l(e) denote the length of an edge e (the specific units of length are not important). m = min l(e) and M = max l(e), where the min and max are taken over all edges on the surface. It is desirable that M/m < 20 and m > 0.1
9. Let a(T) and A(T) denote, respectively, the smallest and the largest angle (in degrees) in a triangle T. Let p = min a(T) and P = max A(T), where the min and max are taken over all surface triangles. It is desirable that p > 5 degrees and P < 175 degrees.

A large number of currently available CAD files representing realistic platform models have the potential of being utilized for electromagnetic simulations and analyses, possibly after some preprocessing.

Model Repair

GeomFix is an interactive software environment for managing configuration and correcting geometry of surface models in order to transform a given model into a computational mesh. GeomFix offers a series of tools for modifying CAD files. Some Geomfix tools provide fully automated solution, while others rely upon interactions with an engineer, since some modifications may be application specific and therefore require human judgement.

Information about GeomFix is available at http://www.matis.net/

Model File Formats

      1 1978 384011520       0
      1 3840
-1.20900e+02 0.00000e+00-2.16800e+02-1.31900e+02 0.00000e+00-2.14900e+02
-1.20900e+02 7.10000e+00-2.16600e+02-1.31900e+02 7.00000e+00-2.14700e+02
-1.20900e+02 1.41000e+01-2.16000e+02-1.31900e+02 1.40000e+01-2.14200e+02
.
.
.
      1       2     -3       3       2     -4       3       4     -5       5       4     -6       5       6     -7       7
.
.
.

Here the first line describes number of components (1), followed by number of vertices (1978), followed by number of facets (3840), followed by the trippled number of facets (11520).

The second line specifies the index of the 1st facet of the 1st (and the only) component followed by the index of the last facet of this component.

The third line lists coordinates of the first two vertices, the next line line lists coordinates of the next two vertices and so on...

Once all vertices have been listed, the list of facets starts in the following manner:
Index of the 1st vertex of the 1st facet is followed by the index of the 2nd vertex of the 1st facet, which is followed by the index of the 3rd vertex of the 1st facet and so on. The last index of each facet is preceded by the minus sign.

The DOVA working format is an example of a polygonal mesh. There are many different polygonal meshes that are used to approximate a smooth surface for electromagnetics, rendering, stereolithography, VRLM, finite element analysis, animation, medical imaging etc. There are converters/translators between different formats available.

Many CAD systems now generate surfaces as connected patches of non-uniformed rational B-splines (NURBS) to represent 3-D geometry. CAD systems usually offer an option to translate the NURBS into polygonal meshes.

Antennas

Similar to other EM codes, [1], [2], we use the representation of antennas based on the Green's function solution available for infinitesimally small current elements. To account for the finite sizes of antennas, pattern factors are used as multiplicative factors in the UTD field expressions.

Bibliography

1.   W.D. Burnside, J.J. Kim, B. Grandchamp, R.G. Rojas, W. Law, Airborne Antenna Radiation Pattern Code User's Manual, Rep. No. 716199-4, The Ohio State University ElectroScience Laboratory, 1985, Columbus, OH

2.   R.J. Marhefka and W.D. Burnside,   Numerical Electromagnetics Code - Basic Scattering Code - (BSC) (Version 2) Part 1: User's Manual, The Ohio State University ElectroScience Laboratory, 1982, Columbus, OH

3.   S.W.Lee,   Basics, In Antenna Handbook,Theory, Applications and Design, New York, 1988. ed. by Y.T. Lo, and S.W. Lee, Van Nostrand Rheinhold Co., New York, NY, 1988

4.   S.W. Marcus",   "Description of the ECAC Far-Field Smooth Earth Coupling Code (EFFSECC)", ECAC-TN-80-014, DoD ECAC, August 1980, Annapolis, MD

5.   V. Oliker and P. Hussar,   UTD analysis of inter-antenna {EMC} on fully realistic aircraft models, Proceedings of the 1997 Electromagnetic Code Consortium Annual Meeting, USAF Wright Laboratory, Wright Patterson AFB, OH, May 1997

6.   J. B. Keller,   Geometrical theory of diffraction, Journal of the Optical Society of America, 52:116-130, 1962

7.   R.G. Kouyoumjian and P.H. Pathak,   A uniform geometrical theory of diffraction for an edge in a perfectly conducting surface, Proceedings of the IEEE, 62:1448-1461, November, 1974

8.   P.H. Pathak,   Techniques for high-frequency problems, In Antenna Handbook,Theory, Applications and Design, New York, 1988. ed. by Y.T. Lo, and S.W. Lee, Van Nostrand Rheinhold Co., New York, NY, 1988

Installation

To install DOVA on your SGI computer:

1. Make a directory on your machine, which shall henceforth be known as: your_dova_directory (the assumption is made that your_dova_directory is a full path name starting with "/", e.g. /usr/people/guest/DOVA).

2. Move the tar file dova.tar to your_dova_directory and type the commands:
   cd your_dova_directory
   tar xvf dova.tar

   There should now be three subdirectories of your_dova_directory:

   1. EXE, which contains the executables (and help) for dova
   2. MODELS, which contains the representions of models in byu format used in the runs
   3. Projects, which contains the input and output from the runs.

3. Next you must modify the environment. Add your_dova_directory/EXE to the environment variable PATH. Then define DOVA_DIR to be your_dova_directory.

   If using csh, you may do this by ending ~/.cshrc with the lines:
   set path=(your_dova_directory/EXE $path)
   setenv DOVA_DIR your_dova_directory

   For other shells, end ~/.profile with the lines:
   PATH=your_dova_directory/EXE:$PATH
   DOVA_DIR=your_dova_directory
   export PATH DOVA_DIR

4. Finally, create the file your_dova_directory/license containing the password obtained from Matis, Inc. This is based on the serial number of your SGI machine. You should now be able to execute DOVA by typing DOVA in a new shell window.