Antenna Scatterers Analysis Program

Original Thesis

{The document was scanned from the original using Optical Character Recognition in December 1997. Some errors or variations from the original may exist. Comments added to clarify points that may not be obvious or to indicate changes to the original document are inclosed in curly braces "{ }" such as this introduction. Some corrections (e.g. spelling) and format editing were made without indication. Comments, editing, and scanning by R.L. Cross, December 1997 - January 1998}


Monterey, California



Antennas-Scatterers Analysis Program, A General Purpose User-Oriented Computer Program For Analysis of Thin-Wire Structures in the Presence of Finite Ground

Jerry Wayne McCormack
December 1974

Thesis Advisor: R. W. Adler

Approved for public release; distribution unlimited.

Prepared for:

Naval Electronics Laboratory Center San Diego, California 92152

Monterey, California

Rear Admiral Isham Linder

Jack R. Borsting

This thesis prepared in conjunction with research supported in part by Naval Electronics Laboratory Center under Project Number N0095375P000002

Reproduction of all or part of this report is authorized.

Released as a Technical Report by:

{signature illegible}
Dean of Research

[ Image of Report Documentation Page ]


Previous computer programs to solve the electro-magnetic equations for thin-wire radiating structures have been coded in one of two forms; the very limited specialized form or the comprehensive all-encompassing form. Thus, the beginning user, engineer or student, must possess expertise in computer programming as well as in electro-magnetic theory. This thesis develops a computer program which can be used by the student to gain insight into wire radiating structures and, at the same time, be used by the engineer to obtain the expertise necessary to utilize the more comprehensive programs.


I wish to express my deepest appreciation to Professor R. W. Adler for his guidance and counseling during the development of this thesis. I an also particularly grateful to Professor J. H. Richmond for his comments and recommendations.

{Signed} Jerry W. McCormack


Although many thin-wire computer programs have been developed for the purpose of analyzing antennas and scatterers, few of these programs have been directed toward the student of electro-magnetic theory. The majority of the programs are directed to the engineer or advanced student for the purpose of analyzing designed structures or verifying experimental data.

The purpose of the study is to develop a computer program by modifying an existing computer code which can be utilized as an educational method to develop insight into radiating structures by the beginning student of electro-magnetic theory.

The modified Ohio State University Antennas-Scatterers Analysis program (OSUMOD or ASAP) is directed toward the beginning student who does not yet have the expertise necessary to manipulate the input data for proper execution of the larger more comprehensive analysis program. Even though ASAP is small in core requirements and is fast in run time, it is capable of analyzing structures to assist the engineer with design problems.

{Several different versions of the program have been compiled with different limits on the number of 'monopoles' and nodes. The following statements concerning the problem size in the original text are for the original version only.}

Since the resulting program, ASAP, is primarily directed toward students, the {original} program has been {was} limited to structures which contain less than 50 monopoles (segments), no longer than one-fourth of a wavelength, and which have less than 51 nodes (intersections and endpoints). If a ground plane, either perfect or finite is present, the stated limits above are halved due to the generation of an image structure.

{The present form of the FORTRAN source code allows easy changes to the number of elements by changing one PARAMETER statement near the beginning of the program and recompiling. Most PC versions are at least 100 segment and some are 1500 segments. The statement concerning the generation of an image structure remains true; only half the maximum can be used if a ground plane is called for.}



Reference 1 presents the electro-magnetic theory for the analysis of antennas and scatterers in an isotropic, linear, and homogeneous ambient medium. The analysis is performed in the frequency domain with an excitation caused by either a generator or an incident wave.

In the analysis, a piecewise-sinusoidal expansion is used for the current distribution, The matrix equation Z I = V is generated by enforcing reaction tests with a set of sinusoidal dipoles located in the interior region of the wire. Since the current distribution has the same form as the expansion mode, this formulation is known as the "sinusoidal reaction technique"


Reference 2 presents the computer program corresponding to the theory presented in Ref. 1.

1. Input Format

In the {Richmond's original predecessor to ASAP} program, the input data must specify the frequency, wire radius, wire conductivity, the parameters of the exterior medium, coordinates of the points to describe the shape and size of the wire configuration, a list of the wire segments, and the indicators for the various outputs. Table 1 is the input data necessary {for the pre-ASAP program} to analyze a half-wave dipole.

table 1 scanned from original document

2. Output Format

In the original form, the only outputs which could be requested by the input data stream are the following:

a. Antenna Problems
(1) Current Distribution on the Structure.
(2) Input Impedance.
(3) Radiation Efficiency.
(4) Near-Zone Field.
(5) Far-Zone Field.
b. Backscattering Problems
(1) Absorption Cross Section.
(2) Scattering Cross Section.
(3) Extinction Cross Section.
(4) Complex Elements of the Polarization Scattering Matrix
c. Bistatic Scattering Problems
Echo Area.

Table 2 is an example of the output data available for data of table 1.

table 2 scanned from original document


Although the {predecessor to ASAP} program can analyze a structure with up to 50 segments, 55 points and 60 dipoles nodes; it can not analyze a structure in the presence of a finite ground plane.


A. Input Format

As illustrated in table 1 the format for the input data cards is not self explanatory. This format can be determined by referring to the FORMAT statements of the program of Ref. 2. Since the codified program is directed towards the student, the input data format was changed to allow free format. Reference 2 was written in a form which permitted modifications to allow flexibility in specifying input data for the analysis program. Appendix B, titled "User's Manual", discusses the input data cards necessary for proper execution of an analysis problem. Appendix B is self contained and may be used independently of the remainder of this document.

B. Output Format

In the original {Richmond's} computer program, the absence of labels encumbered the output data and lessened the usefulness of the program. To improve the usefulness of the codified version, detailed labels were added to the output data. As with the input data, Ref. 2 was written in a form which enabled modification to allow more specific output data for the analyzed problem. With the addition of the polar plotting package, the far-zone electric field intensity polar radiation and reradiation patterns can be plotted. A sample problem can be found on page 120 in Appendix B, User's Manual. {More detailed examples can be found on the Examples page.}

C, Finite Ground

To enable the student or the engineer to have an improved analysis program, the finite ground effects were added to ASAP. The theory corresponding to the ground effects, which utilize Fresnel reflection coefficients, is discussed in Appendix A, titled "System Manual" . Also discussed in Appendix A is the modified computer program and the corresponding theory. The electro-magnetic theory was developed in Refs. 1, 2, and 3; and it is restated with its corresponding computer code to assist in the understanding of the methods applied. Appendix A is self-contained and can be used independently of the remainder of this document.


The addition of ground effect techniques to the original program did not alter the accuracy or the computational capabilities of the program. The ground effect techniques utilized the results of the original program and modified these results to account for the effects of the presence of the finite ground.

To verify the numerical results of ASAP, the input impedances of both a horizontal and a vertical dipole were compared to the solutions of the exact form of the Sommerfield's equation. As can be seen in table 3 the finite ground treatment of ASAP agrees favorably with Sommerfield's solutions. The ASAP finite ground results are also in excellent agreement with the previous computer solutions of Refs. 4 and 5.

table 3 scanned from original document


Although the program is a general analysis tool for students, several future modifications will enhance the program as a design tool for engineers. These items include: varying the wire radius on the structure; incorporation of non-radiating elements such as transmission lines; varying the wire insulation radius, conductivity, and dielectric constant; and a geometry generation package such as dipole array or helix. One major change that would both improve the speed and reduce the core requirement is that of symmetry. No attempt was made to utilize the symmetry in the admittance matrix when the ground plane is present. If symmetry were applied, the structure size limit with the ground plane present would be approximately that of the structure without the ground plane.

APPENDIX A Systems Manual (Theory of Operation from Thesis)

APPENDIX B User's Manual (from Thesis)

User's Manual (from Thesis)

The quick reference for the user's guide.

Systems Manual (Theory of Operation from Thesis)

Download Source and PC executables

Examples page

ASAP Thesis References

Last modified on: Saturday, 3 Nov 2007.

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