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Computers in Amateur Radio

Antenna Modelling

by Ian Birkenshaw, G4UWK

Introduction

The average computer-literate radio amateur might initially ask why he

should bother with antenna modelling, not being an antenna designer or

guru. However, every amateur is faced with limitations imposed by real

estate, available supports, planning permission from the XYL, neigh-

bours or local council and will want to maximise the radiated signal from

his QTH within these restrictions.

Antenna modelling using a home computer can answer many

questions, particularly in comparing one possible antenna against

another. It can also answer questions about the real performance avail-

able from commercial antennas, often described in glowing terms by

manufacturers or suppliers.

All antenna modelling software likely to be of interest to the typical

amateur is based around a modelling system called ‘Numerical Electro-

magnetic Code version 2’ or NEC2. This was created in 1981 by the

Livingstone Livermore Laboratories in California, the original client being

the US Navy. Initially the system was classified, but over the years

became available for general use. Originally written in FORTRAN, the

code has been translated over the years for use by the Microsoft Win-

dows operating system.

An intermediate version written in BASIC for early PC’s called

MININEC also exists, but has a number of problems due to it being a

cut-down version of NEC2.

NEC2 works by breaking the radiating elements of the antenna to

be modelled into small portions called ‘segments’ and summing the

overall electromagnetic radiation from the current and phase on these

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