Available Technology

Numerical Electromagnetics Code (NEC) 5.0

Background:

Antennas are a foundational component of our global communication and information systems. Cell phones, Wi-Fi networks, and satellite links couldn’t exist without them. Through much of the 20th century, antenna designers used hand calculations to model and fine tune their antennas. ; However, as antenna designs grew more sophisticated, hand calculations became inadequate. In the 1960s, researchers used computers to develop their antennas, but the performance improvements were incremental. By the 1970s, the U.S. Navy needed to improve their ship-mounted antennas, specifically those that supported their communication and radar systems. The Naval Ocean Systems Center and the Air Force Weapons Laboratory turned to LLNL for a solution.

Utilizing the Method of Moments calculation (a method of estimation) technique, LLNL scientists, Gerald Burke, Andrew Poggio, and Edward Miller created the Numerical Electromagnetic Code (NEC), an antenna modeling system for wire and surface antennas. NEC’s ability to more accurately calculate currents along the antenna wires, and the junctions between them, offered a significant improvement over the antenna modeling program that was being used at the time. NEC became a game-changer for antenna mapping and was quickly pressed into service. The code gave the Navy insight into how a ship’s structure would affect an antenna’s performance and informed modifications to both ship and antenna designs. The result was significantly improved radar and communication systems that saved time, money, and resources.

As computer capability to handle heavy calculations increases, new versions of the code have been released. NEC-3 and NEC-4 have been the most licensed technology in LLNL’s software portfolio, and the most widely used code for analyzing antenna performance. The original code and NEC-2 are still available to the public. NEC-4, which is still licensed by LLNL for end users, solves the Electric Field Integral Equation (EFIE) for wire structures and the Magnetic Field Integral Equation (MFIE) for surfaces. NEC-5 is the latest version of LLNL’s decades-long successful NEC antenna modeling software family.

Description:

NEC-5 models the electromagnetic response of antennas and scatters consisting of wires and conducting surfaces. Input commands can generate a number of wire and surface shapes that can be combined for complex models. Excitation can be voltage or current sources or incident plane waves. Models can be above or buried in a homogeneous ground and can include impedance loads, networks and transmission lines. Output can include model currents, radiation patterns and near E and H fields.

NEC-5 differs from NEC-4, which solved the electric field integral equation with point matching of the field. The mixed-potential solution method in NEC-5 is more accurate for modeling surfaces and wire-surface connections and offers a more stable solution in other respects.

NEC-5 Updates:

NEC–5 is a new departure for NEC, solving the Electric Field Integral Equation (EFIE) for wires and surfaces using the Mixed-Potential method with triangular and roof top basis functions as developed by Rao, Wilton and Glisson (May 1982). This method, while new to NEC, is used in many other codes, since it offers advantages over the method used in previous NEC codes.

NEC–5, like previous NEC codes, is written in Fortran. Arrays are allocated at run time, so there are no limits on the model size except for available memory. The “out of core” solution in previous NEC codes is not available in NEC–5 so available RAM or virtual memory will limit model size.

NEC–5 includes an interactive mode that provides basic model plots that can show element numbers and segment end and edge numbers and can show the currents once a solution has been obtained.

NEC-5 can be used independently or with a graphical interface called NEC5GI. NEC5GI has dialog boxes for building all input commands with a graphical display as the model is built. When a solution has been obtained, NEC5GI will display the model and currents and provides 2D and 3D plots of radiation patterns.

NEC–5 reflects its NEC heritage in the input command structure and output, as much as possible compatible with NEC–4, and modeling features for excitation a ground interface, loading, networks and transmission lines.

Potential Applications

Moment method codes such as NEC–5 can be used to model a wide variety of antennas and scatterers including antennas in complex environments such as ships and aircraft. However, since the computer time and resources required by the moment-method solution increase with increasing size of the model relative to the wavelength, the solution may become difficult or impractical for large structures at high frequencies. The approach used in NEC-5 is most applicable to the types of problems encountered at high frequency (HF), very high frequency (VHF) and lower frequencies.

Development Status

LLNL has asserted copyright in NEC-5.

LLNL is offering End User License Agreements to NEC-5 https://ipo.llnl.gov/technologies/nec. In addition, commercial software vendors with a demonstrated ability to bring technologies like NEC-5 to the market are encouraged to respond to this announcement. LLNL will consider commercialization through qualified licensees to further distribute and support NEC-5.

Technology Type(s): 
antenna design software
Internal Laboratory Ref #: 
NEC
Lab Representatives
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