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The Numerical Electromagnetics Code, or NEC, is a popular antenna modeling system for wire and surface antennas. It was originally written in FORTRAN in 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 modelling 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. Later versions, NEC-3 and NEC-4, are freely available as compiled binaries but have not been nearly as popular. ==History== The code traces its history to an earlier program, BRACT, which was used to analyze antennas consisting of many thin wires in free space. It was useful for modeling certain common types of antennas used on aircraft or spacecraft or other examples where the ground was far enough away that it did not affect the signals. BRACT was developed in the early 1970s by MBAssociates for the US Air Force's Space and Missile Systems Center. MBAssociates, named after the founding partners of Bob Mainhardt and Art Biehl, are better known for the development of the Gyrojet rocket gun. BRACT's success led to a second contract with MBAssociates, this time by the Naval Research Laboratory and USAF Rome Air Development Center, to adapt the BRACT code to consider the effect of the ground. This produced the Antenna Modeling Program, or AMP, which was extensively modified to support disk based files, simplify the input and output to make it easier to use, and extensively documented. A follow-up, AMP2, added calculations for extended surfaces like reflectors. NEC is an advanced version of AMP2, with more options and features. It was written by programmers at Lawrence Livermore National Laboratory (LLNL) under contract to the Naval Ocean Systems Center and the Air Force Weapons Laboratory. The original NEC added a more accurate system for calculating currents along the wires, and at junctions between them, as well as an option that increased the accuracy when the wire was thick, with a low aspect ratio compared to its length. NEC-2 added two major features, a numerical Green's function for working with large planes, and an expansion of the ground-plane code to deal with partially lossy materials that are more realistic for antennas near the ground. With the release of NEC-2, the original became known as NEC-1. All of these programs originated in the mainframe era, originally running on Control Data machines and later ported to the VAX. The code was written in FORTRAN and designed to take input from punch card stacks in column-delimited format and then print the results on a line printer. These early versions were widely ported to a number of other big-iron platforms, and a profusion of slightly different versions resulted. A variety of microcomputer based versions using FORTRAN compilers appeared during the late 1980s, often limited by the need to fit into the MS-DOS 640 kB memory footprint. Modern versions normally port the original code to the C programming language, either using automated tools or hand-converted code. C versions have formed the basis for most modern microcomputer versions, and runs on a wide variety of platforms. Modern programs using the nec2 code generally use a graphical user interface (GUI) to provide an editor system that then converts the user's input into a virtual deck of punch cards, passes that as input to the otherwise unchanged nec2 code, and the parses the output to turn it back into GUI output. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Numerical Electromagnetics Code」の詳細全文を読む スポンサード リンク
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