Numerical Electromagnetics Code

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The Numerical Electromagnetics Code (NEC), credited to Gerald Burke, is an algorithm and generic computer application, originally written in FORTRAN. Developed in the 1970s, it is a popular antenna modeling method for wire and surface antennas. The code was made publicly available for general use and has subsequently been distributed for many computer platforms from mainframes to humble PCs.

Contents 1 How It Works 2 NEC Versions 3 NEC In the Field 4 Limitations 4.1 Public Domain Resources 4.2 Commercial Resources

[edit] How It Works

NEC models can include wires buried in a homogeneous ground, insulated wires and impedance loads. The code is based on the method of moments solution of the electric field integral equation for thin wires and the magnetic field integral equation for closed, conducting surfaces. The algorithm has no theoretical limit and can be applied to very large arrays or for detailed modeling of very small antenna systems.

Models are defined as elements of wire or similar as an input text file (typically in ASCII). They are then input into the NEC application to generate tabular results. The results can then be input into subsequent 'helper' applications for visual viewing and the generation of other graphical representations as smith charts, etc.

[edit] NEC Versions

There are at least four versions of NEC, with NEC-2 emerging in 1981 and NEC-4 appearing in 1992. NEC-2 is the highest version of the code within the public domain without license. NEC-4 remains proprietary with the Lawrence Livermore National Laboratory and the University of California.

NEC-4 currently requires a separate license for use. The licensing details are available from Lawrence Livermore National Laboratory here.

MININEC was a version first written in BASIC for home computers. It first emerged in 1982 on the Apple II computer. MININEC computational engines are now written in FORTRAN to improve speed. MININEC is an independent implementation of the method of moments. The basic algorithms are based upon the advice of Professor Wilton at the University of Mississippi (now with the University of Houston).

MININEC suffers from some known flaws compared to NEC, the best known being that resonant frequencies may be slightly in error.

[edit] NEC In the Field

Although antennas can be simple structures, the modeling of these systems does require a certain level of understanding of the electrical characteristics of antennas.

As a starter for any modeler, 4nec2 or EZnec can be used. See their respective home pages for further information on their purchase and/or installation.

[edit] Limitations

• NEC-2 cannot model tapered elements such as those made of telescoping aluminum.
• NEC-2 cannot model buried radials or ground stakes.

[edit] Public Domain Resources

• 4nec2 (web archive backup) is a completely free NEC2/NEC4 implementation for windows. It is a tool for creating, viewing, optimizing and checking 2D and 3D style antenna geometry structures and generate, display and/or compare near-field/far-field radiation patterns for both the starting and experienced antenna modeler. You can get 4NEC2 from Arie Voors' homepage.
• Cebik antenna pages - A great repository of antenna modeling and related information of which this page has much to say on antenna modeling.
• Numerical Electromagnetics Code NEC2 unofficial home page - NEC2 documentation and code examples
• MMANA - A free antenna modeling program based on MININEC.
• Xnec2c - A translation of NEC2 into C, NEC2C, and a GTK2 based GUI, Xnec2c.

[edit] Commercial Resources

• EZnec - A well known commercial-based antenna modeling package based on NEC3 and NEC4.
• NEC4WIN NEC4WIN /VM - A Windows XP, Vista simulation program based on Mininec 3.
• AC6LA antenna utilities - A collection of commercial antenna utilities
• Nec-Win plus - A commercial modeling package.
• GAL-ANA - A commercial antenna modeling package based on NEC2 and MININEC.