NEC Structure Interpolation and Gridding (SIG) program

I posted an announcement of a package we have developed on this list
about 1 year ago. Quite a number of people purchased the package
since and the list have also grown considerably. I am hence taking
the opportunity of reposting a quick overview for people who have not
seen it before:

ANNOUNCEMENT: Structure Interpolation and Gridding (SIG) program for NEC2
=========================================================================

1.0 Overview

The Structure Interpolation and Gridding (SIG) program is a stand alone
program which processes cross-sectional data representing a complex three
dimensional object and generates a wire grid NEC geometry file.
The program was designed in accordance with the Object Oriented
Paradigm (OOP) and implemented in the C++ language.

The program was developed by Andre Fourie, Derek Nitch and Ofer Givati
[see references 1 and 2 for a detailed description of SIG]
and has been successfully used for aircraft simulation/scale model
measurement studies in the HF, VHF and UHF range by Ofer Givati and
Andre Fourie [reference 3 gives details of a fighter plane study using
SIG]. Other studies involved a helicopter and a C-130 transport plane.

The program was developed as part of the Computational Electromagnetic
Research done at the University of the Witwatersrand, and a company, EM
Simulations (Pty) Ltd was formed to market software produced. The
intention is to use income generated from software sales towards
further research and development of both Method of Moment pre- and post-
processors, as well as new Method of Moment Software.

2.0 Machines, Operating Systems and Availability

The program is compiled for 80386/80486 processors running under Windows
3.1. A version compiled for the 80286 processor running under DOS5.0
is also available. The program, accompanied by a 75 page user manual is
available for $400.00 + $15.00 postage.

3.0 SIG Features

a) A wire grid geometry is generated by SIG for the complete structure
(fuselage, wings, fins etc) without requiring different parts to be
seperately modelled.

b) Model generation with the same input file at various frequencies is
possible.

c) Segment length can be varied throughout the structure.

d) Cutting planes and angles can be specified; this removes parts of the
structure at the user's discretion to reduce problem size.

e) Segment radii are automatically calculated by the package to
obtain a wire surface area approximately twice the wire surface area of the
structure.

f) Even when structure dimensions are changing between user-defined cross
sections approximately correct longitudinal segment lengths are obtained.

g) Symmetry about the x- and y-planes can be specified. In such cases,
the segmentation method takes this situation into account, and
segments abutting the symmetry planes will be half the normal length - no
longitudinal segments will be produced on the symmetry plane.

h) Simple, but effective, visualization and hard copy features are
provided by producing output files in the 3DV public domain viewer format.

i) Combinations of wires and surfaces such as monopoles on finite ground
planes, as well as pure wire structures such as skeletal wire biconical
antennas, can also be segmented using SIG.

4.0 USAGE

a) User selects definitive cross sections of aircraft or other
structure which must be segmented/gridded. Each cross section is
further subdivided and tagged in terms of curves (eg. on line curve
may represent a wing and another elliptical section some part of the
fuselage). The curve tags are used to identify which portions link up
with each other in different cross sections, and this technique is
really the crux of the method since it allows complete and complex
structures to be gridded and joined correctly. Even wires are
accomodated since a single point curve in one cross section with a
and one with the same tag in the next cross section will describe a
correctly segmented wire when interpreted by SIG.

b) The cross sections are manually entered into an ASCII file in
terms of x y coordinate pairs.

c) The SIG program is executed and the user can then:
  i) Create interpolated cross sections (and view then using the
 3d viewer to confirm that the entered cross sections provide the
 required definition)
 ii) Request full gridding for the frequency specified and also view
 the fully gridded structure in the 3D viewer. The 3D viewer allows
 real time rotation of the structure using the mouse which is a great
 aid in identifying problems.
 iii) Output the NEC file (Comment cards up to end of geometry
 definition ie GE card).
 iv) User can also output an HPGL format file of any 3D structure for
 later printing or documentation.

d) After this the user can add excitation and other control cards to
 the NEC file produced by SIG and run the problem.

5.0 REFERENCES

[1] APC Fourie, DC Nitch and O Givati, "A Complex-Body Structure
Interpolation and Gridding Program (SIG) for NEC", IEEE Antennas
and Propagation Magazine, Vol 36, No3, June 1994, pp 85-89.

[2] APC Fourie, DC Nitch and O Givati, "A Complex Structure
Interpolation and Gridding program (SIG) for NEC", Proceedings
of the IEEE Antennas and Propagation Society International Symposium,
Seattle, June 1994, pp 1154-1157.

[3] O Givati and APC Fourie, "Radiation Patterns of Antennas Mounted on a
Modified Mirage Aircraft", Proceedings of the IEEE Antennas and Propagation
Society International Symposium, Seattle, June 1994, pp 1158-1161

e-mail: fourie_at_odie.ee.wits.ac.za
Tel: intl + 27 11 716 5386
Fax: intl + 27 11 339 4610
Address: Dr. APC Fourie, Dept Elec Eng, PO WITS, 2050, South Africa

e-mail: fourie_at_odie.ee.wits.ac.za
Tel: intl + 27 11 716 5386
Fax: intl + 27 11 339 4610
Address: Dr. APC Fourie, Dept Elec Eng, PO WITS, 2050, South Africa
Received on Mon Nov 06 1995 - 18:00:00 EST