Antenna Modeling Programs and Resources

L. B. Cebik, W4RNL

wpe4E.jpg (1131 bytes)uch of my antenna research work is based on systematic antenna modeling in a version of the Numerical Electromagnetics Code (NEC). The following brief notes will provide links to known antenna modeling software providers.

NEC-4

The latest version of NEC is NEC-4, which overcomes most of the shortcomings with earlier codes. It permits the modeling of underground radial systems, elements of varying diameter sections, carefully-constructed close-spaced parallel wires, as well as all the modeling capabilities of earlier versions of the code. NEC-4 is a proprietary code of the Lawrence Livermore National Laboratory and the University of California, from whom a user-license must be obtained. Export restrictions may apply. The current cost of licensing is $250 for academic or non-commercial users and $950 for a Commercial Executable License. You may obtain the license materials on line at the LLNL site.

At present, I know of only two sources of commercial software for NEC-4:

Roy Lewallen, W7EL produces EZNEC Pro, which has an option for NEC-4, if the purchaser has a confirmed license for NEC-4. EZNEC Pro and EZNEC Plus are also available for NEC-2 (see below). W7EL also makes available EZNEC (v. 4.0), a segment-restricted version of NEC-2. The latest W7EL NEC software packages are Windows-based and employ similar user interfaces which have earned praise in DOS versions for their user-friendliness. New versions of EZNEC contain a 3-D plot graphic that can be "sliced" for select 2-D patterns, direct entry for trap as well as for series and parallel R-L-C loads, and the average gain test. EZNEC also implements the NEC2/NEC-4 ground wave (RP1) output. Wire construction features are limited to GW commands, but include special facilities for creating rectangular wire grids, radial systems, circles, and helices. EZNEC Pro will import or export files in .NEC format. Special processing has increased the segment limit to 20,000.

Nittany Scientific produces a 32-bit Windows version of NEC-4 called GNEC. This program implements all all of the input cards of the complete NEC-4 input deck, thus permitting the use of catenary wires, helices, networks, rotational and linear structure movement, and coordinate and rotational based symmetry options. Control commands include the insulated sheath, near fields in both coordinate and axial form, the upper medium, as well as far-field and ground wave analysis. Output capabilities include 3-D, polar plots, and many rectangular (X-Y) graphs, as well a a large array of tabular reports and the Average Gain Test. A special insert using the NEC-Win Plus interface allows modeling by equation. The basic ASCII interface uses assist screen to formulate each command entry and is similar to the one used in NEC-Win Pro, described below under NEC-2.

NEC-2

NEC-2 is a highly capable version of the code which is in the public domain. It is restricted to antenna elements of a single diameter (although some software providers have introduced corrections for linear elements whose diameters varies). It cannot handle buried radial systems, although above ground systems close to the earth can be handled. However, it is equipped with the Sommerfeld-Norton high accuracy ground model for accurate modeling of horizontal wires close to the earth.

Nittany Scientific produces a Windows version of NEC-2 called NECWin Plus, which features a true spreadsheet geometry construction page set with design-by-equation capabilities. The program also offers stepped-diameter corrections, Gain Averaging Test, CAD (.DXF) file input, 2-D and 3-D plots and antenna views, and graphical outputs. NSI considers this to be an entry level program and offers a companion volume with exercise models called Basic Antenna Modeling: A Hands-On Tutorial.

The company also offers a research NEC-2 program: NECWin Pro (NWP). NWP employs a user-selected choice between a spreadsheet geometry construction page (adapted from NEC-Win Plus, or the normal ASCII model input page with help screen/windows for all antenna model input parameters. In addition, NWP provides direct entry or importation of NEC model inputs and provides a large assortment of available rectangular output graphics, along with other advanced NEC capabilities. NSI views NEC-Win Pro as a profession-level program.

Recently added to NSI offerings is NEC-Win Synth, a program to synthesize wire-grid structures for use in any NEC (-2/-4) program. The user may select a preset shape and enter critical dimensions or synthesize a structure with the spreadsheet entry facility. NEC-Win Synth can be directly linked to NEC-Win Plus or save its output in a standard .NEC file.

EZNEC for Windows, both in basic and professional versions, is available from Roy Lewallen. See the general description of EZNEC/ELNEC products under NEC-4 above. EZNEC 4.0, the basic version of the NEC-2 programs, offers 3-D plots with 2-D slicing, ground-wave output, stepped diameter correction, and numerous short-cuts to antenna geometry modification. As well, there are new facilities for entering traps and considerable annotation capabilities. Standard EZNEC is restricted to 500 segments. EZNEC Plus offers additional wire construction and movement capabilities, along with a 1500-segment limit. EZNEC Pro M offers all of the features of EZNEC Pro/4, with the exception of being limited to the use of NEC-2.

NEC2GO, a general purpose Nec-2d interface to Windows, is available from Nova Plus Software. It provides "Modeling by Equation," sweeping of variables, and support for Coax and Ladder Line feedlines to show impedance transformation and loss. Features include unlimited segments, sources, and loads, shifting and rotating wire definitions, automatic segment generation and Tapering, Auto Gain Test and Average gain, quick convergence testing, automatic creation of plots at max gain angles, LAPACK routines, all NEC ground options, and NT-based feedpoint matching networks. The program is fully Windows compliant with no DOS executables. A free Demo Version is available.

4NEC2 is a no-cost experimental version of NEC-2, with continuous development of its facilities and interface by its programmer, Arie Voors. Since the program changes with regularity as Arie introduces new features, such as improvements to the user interface and an optimizer, a detailed description is not feasible here. The program can be downloaded freely from the unofficial NEC Archives.

Poynting Software is making available version 2.5 of its hybrid NEC-2/UTD program "SuperNEC," which is implemented in C++. The program has a parallel execution option. It makes use of MatLab 5.2 to run the program and avails itself of MatLab's many input and output facilities, such as the use of MatLab language assemblies that users may add to or modify. A version (SuperNEC Lite) which is restricted to 300 segments and 3 GTD objects is available at a student price, and a demo is available at the web site.

Expert MININEC

Before recent advances in speed and memory, it was not feasible to run NEC on a PC. Rockway and Logan developed MININEC, a Basic language adaptation of NEC for PCs. More recently, they have advanced the MININEC algorithms and code to overcome many of its initial limitations. The "new" MININEC can handle sharp angles in antenna geometry directly (without segment length tapering) and handles antennas close to ground with much better accuracy. However, the MININEC Professional code (as well as the input/output interfaces) is a proprietary product.

EM Scientific offers several levels of Expert MININEC Professional, ranging from the basic level MININEC for Windows to MININEC Broadcast Professional. The product-level distinctions include the number of segments and unknowns available; advanced features of geometry, electrical, and solution description; and auxiliary calculations. These are all Windows products.

MININEC 3.13

The public domain MININEC code (version 3.13) is available with several commercial user interfaces, as indicated in these notes. For general antenna analysis that does not press its limitations, MININEC is a highly competent code. It handles elements of changing diameter directly, and with segment-length tapering, can accurately model a wide range of antenna geometries. However, horizontal antennas must be at least 0.2 wavelengths above ground for accurate results. Moreover, specification of ground conditions affects only antenna far field results, but not feedpoint conditions.

Antenna Model, (from Teri Software) which first appeared in a DOS version in 1992, has returned with an advanced Windows version of MININEC based on 3.13. Wholly reprogrammed, the core has virtually unlimited segment capacity for models and uses revised (and sometimes alternate) algorithms to overcome MININEC difficulties with errors with increasing frequency, angular junctions, wire junctions less than 28 degrees, and wires spaced closer than 0.23 wavelengths. The program offers both 2-D and 3-D patterns, and a variety of supplemental calculating features, for example, inductor calculations that include leads and distributed capacitance and matching networks including gamma, Tee, and beta (or hairpin). The program also permits for each wire separate values of conductivity and permeability.

Orion of Canada offers a Windows95/98/NT 32-bit version of MININEC, NEC4WIN, using a spreadsheet geometry input page, pull down boxes for other antenna parameters, and a pattern plotting output that includes lobe identification and bandwidth. In addition, the user can vary the height of the antenna without invoking a complete recalculation of the matrix for faster results. Recent upgrades include 3-D patterns, and optimization routines. The VM (virtual memory) version of the program permits almost unlimited numbers of segments in a model.

MMANA, version 0.5E (English language), is available as freeware from VK5KC's "MMHamsoft" web site. Based upon public domain MININEC, the program offers a large segment (pulse) capacity because the author, JE3HHT, Makoto Mori, has placed the program in a Windows framework using C++. The program offers advanced features such as segment length tapering, optimizing, and network calculation, but lacks some basic features, such as assigning a user-specified material conductivity or resistivity to the model wires, frequency compensation, or close-wire compensation. However, the price (no-cost) is excellent, although there is no customer support for the package.

Related Modeling Software

MultiNEC by Dan Maguire, is an Excel application that can make multiple simulation runs of an antenna model while automatically changing one or more aspects of the model between runs. The program requires that the user have one of the commercial implementations of NEC-2, a generic NEC-2 core, a NEC-4 program, or the Antenna Model implementation of MININEC. The program is now available in a new upgrade for a very low cost.

NEC-BSC, the NEC-Basic Scattering Code (and its "workbench") and other MoM-related software (including EM Surface Patch Code, Reflector Antenna Code, and Aircraft Code) are available (at about $300 per package) from the Ohio State ElectroScience Laboratory.

The sources listed above have web pages for further information on the relevant software. Brian Beezley, K6STI, also has until recently offered a wide range of NEC-related software, as well as a Yagi optimization program, a terrain analysis program, and DSP software. Contact the author via mail, since the most recent e-mail address (k6sti@n2.net) may no longer be active.

These listings do not include a considerable array of hybrid modeling programs that make use of multiple techniques--many, but not all, MoM based--to model circuitry (usually derived from PSpice lists or outputs), transmission lines, and antennas (including flat surfaces and substrates). Some are compatible with AutoCAD outputs for direct graphic-to-model links. Virtually all of the advanced versions of these programs are proprietary and expensive compared to NEC offerings. However, for many aspects of UHF and EHF design, they be the proper programs of choice.

Some Modeling Information Resources

The (Unofficial) NEC Archives are maintained by Ray Anderson, WB6TPU. Formerly, this collection of NEC-related software has been available only via FTP. However, the entire contents are now accessible via the web. They include many source codes for NEC and for pre- and post-processing of NEC, along with some sample input files. Another valuable website of NEC-2 information was originated by Peter Richeson and is now maintained by Nittany-Scientific. These sites are good sources for downloading the entire contents of the NEC-2 3-volume manual.

There are several self-study modeling courses available. ARRL offer Antenna Modeling in its Continuing Education Series. The 30-lesson course uses EZNEC and NEC-Win Plus to introduce basic modeling concepts, techniques, and limitations related to NEC-2. The volume and the exercise models are available independently of the tutored educational program for self-study purposes. An alternative tutorial geared to NEC-Win Plus is Basic Antenna Modeling: A Hands-On Tutorial. The 300+ page self-study course comes with exercise models and is available at a discount price when purchased in conjunction with Nittany Scientific software.

Editor's Note: antenneX is an authorized distributor for the Nittany-Scientific software NEC-Win Plus+, NEC-Win Synth and the Tutorial Book The products are offered here at this web site in the Shopping Shack for immediate download.

For more advanced users of NEC-2 and NEC-4, NSI is releasing Intermediate Antenna Modeling: A Hands-On Tutorial. This self-study volume encompasses virtually the entire command sets for both cores, including details of command revisions in the transition between NEC-2 and NEC-4. The 450-page volume includes about 300 exercise models in .NEC format. Although geared to the cores used by NSI (NEC-Won Pro and GNEC), the volume is useful with almost any version of NEC-2 or NEC-4.

To examine some of the differences among the NEC and MININEC offerings, see QEX, for Sep/Oct, 2005, and Nov/Dec, 2005. The 2-part series text and graphics provide an overview of significant user differences among programs, many of which appear in the above listing. It can be interesting to compare this overview to an earlier version that appeared in QEX, Mar/Apr, 1998. The differences will show the rate of change and of development in the field of antenna modeling software.

There are--for many reasons--no instructional manuals for MININEC of the scope and independence of the self-study course for NEC. Software instruction manuals or "help" compendiums may be the best source of instruction. However, you may wish to get started by looking back to "A Beginner's Guide to Using Computer Antenna Modeling Programs," from The ARRL Antenna Compendium, Volume 3, reprinted in Vertical Antenna Classics. As well, the antenneX antenna discussion list is a good place to pose questions about both NEC and MININEC, since the list subscribers include very experienced users. Many of these users know of information and software resources that go far beyond what I can include here.

For more details on the use of commands, the limitations of various NEC and MININEC programs, and numerous work-arounds, see the Antenna Modeling series that appears monthly in antenneX. You can freely view past columns (92 of them) at the antenneX web site and at my personal web site. Alternatively, the first 75 columns are available on CD-ROM from antenneX Shopping Shack. Some of the columns are specifically devoted to the limitations of MININEC, of NEC-2, and of NEC-4, and there are numerous basic level items to guide proper use of any of these programs.

This listing is necessarily limited. As with all software information, development efforts quickly outrun written accounts. In addition, there are many valuable articles available on the history of MOM techniques, some of which are referenced within the cited materials. Moreover, there are many gaps in the coverage. Nevertheless, I hope that this brief guide helps you to learn of what is available and to develop a good evaluation of which program may be best for your long-term needs and desires. -30-


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~ antenneX ~ November 2005 Online Issue #103 ~

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