The Numerical Electromagnetics Code, or NEC, is a popular antenna modeling system for wire and surface antennas. It was originally written in FORTRAN during the 1970s by Gerald Burke and Andrew Poggio of the Lawrence Livermore National Laboratory. The code was made publicly available for general use and has subsequently been distributed for many computer platforms from mainframes to PCs.
NEC is widely used for modeling antenna designs, particularly for common designs like television and radio antennas, shortwave and ham radio, and similar examples. Examples of practically any common antenna type can be found in NEC format on the internet. While highly adaptable, NEC has its limits, and other systems are commonly used for very large or complex antennas or special cases like microwave antennas.
By far the most common version is NEC-2, the last to be released in fully public form. There is a wide and varied market of applications that embed the NEC-2 code within frameworks to simplify or automate common tasks. EZNEC is one of those applications provides a UI that wraps the NEC-2 calculations.
For more information on NEC, see this Wikipedia posting:
Upon Roy Lewallen W7EL retirement on Jan 1, 2022, he released EZNEC EZNEC Pro/2 v. 6.0 to the public domain, see https://eznec.com/ A version can be downloaded here: