Numerical Electromagnetics Code

Introduction

The Numerical Electromagnetics Code (NEC), accredited to Gerald Burke, is an algorithm and generic computer application, originally written in FORTRAN. Developed in the 1970s, it is a popular antenna modelling 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.

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 modelling 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 generated 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.

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.

NEC In the Field

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

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

Public Domain Resources

4nec2 is a completely free NEC2/NEC4 implemenntation 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 modeller. You can get 4NEC2 from Arie Voors' homepage here.
Cebik antenna pages - A great repository of antenna modelling and related information of which this page has much to say on antenna modelling.
The Unofficial Nec Archives - A large library of NEC-related items for a large variety of platforms.

Commercial Resources

EZnec - A well known commercial-based antenna modelling package based on NEC3 and NEC4.
AC6LA antenna utilities - A collection of commercial antenna utilities
Nec-Win plus - A commercial modelling package.