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Antenna Modelling

segments to produce the actual radiation pattern in a mathematical

process called ‘Method of Moments’.

Readers with a strong physics or maths background may like to

peruse the original design methodology. It is available on the Internet at:

www.nec2.org

A number of antenna modelling software packages are available

based on NEC2. Some of these are freeware and some have to be

purchased. It should be stated that the original NEC2 software is far from

user friendly. It was written for professional antenna designers using

mainframe computers and requires considerable additional add-ons to

make it more intuitive and easier to use.

All versions define models on a 3-axis grid, X and Y orthogonally in

the horizontal plane and along the Z axis vertically. Some knowledge of

basic geometry (sine, cosine and tangent) is essential to model with

NEC2.

All antenna elements are defined as wires made up as a number of

segments.

A more powerful version NEC4 is available, with additional features

beyond NEC2. This still has a restricted security status and requires the

user to obtain a licence before purchasing the actual software as part of

an antenna modelling package. Unfortunately this costs several hundred

pounds and would only be of interest to the serious antenna designer.

A list of available NEC2 based antenna modelling software is

detailed in Table 4.1.

Table 4.1: NEC2-

based antenna

modelling

software.

Product Supplier Web Site Free

Name Demo

Version?

4nec2 Arie Voos http://home.ict.nl/~arivoors/ Freeware

Nec2Go Nova Plus http://www.nec2go.com/ Yes

Software

EZNEC V5.0 Roy Lewallen http://www.eznec.com/ Yes

W7EL

NEC – Win Nittany http://www.nittany-scientific.com No

Plus Scientific

It is left to the reader to select the appropriate package for them-

selves. They all do basically the same job and any of them will require

an investment in time to get familiar with the features. Obviously the

software available as freeware or as free demo will be more attractive.

Practical Example

We will now model a real life antenna, the popular G5RV multi-band

dipole, complete with transmission line feeder to show how it is done.

We will use the NEC2-based EZNEC program for this.

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