ANTENNA MODELLING

Or

You can’t fall from a keyboard!

Modelling Techniques

• NEC-based Analysis

• Optimization techniques

• Empirical- and Equation-based methods

• Traps, Feedlines, Propagation, etc.

NEC

• Numerical Electro-magnetics Code

• Uses Method of Moments (MOM)

• NEC-2 (Public Domain)

• NEC-4 (License req’d, Export restrictions)

NEC-2 based software

• MININEC (several versions)

• EZNEC2 (dos), EZNEC3 (windows)

• NECWin Plus, NECWin Pro

• 4NEC2

• and several other lesser known (?) programs

MININEC

• Initially in BASIC for small computers

• version 3.13 in public domain

• shortcomings and strengths

• commercial implementations available

• e.g. EM Scientific, Teri Software, Orion, etc

EZNEC

• By Roy Lewallen, W7EL

• DOS, windows, and Professional Versions

• Current windows version 3.0, Price US$89.

• Free demo version available downloadable

• Excellent documentation and support

• (Demonstration)

NECWin

• By Nittany Scientific

• DOS, Windows, and Professional versions

• NECWin Plus, Price US$ 150.

• User friendly

• 400+ page tutorial by L.B. Cebik US$ 50.

Other NEC-2 Based Software

• EZNEC and NECWin for serious Hams?

• Google search will find many others

• Try “Antenna Modelling” or “Unofficial NEC Archives”

• Some have demo versions

4NEC2

• Free “experimental version”

• continuing development (Arie Voors)

• Downloadable from Unofficial NEC Archives

Real and Possible Problem Areas

• Tapered elements

• Grounds

• Wires meeting at sharp angles

• Elevated radials

• Traps

• Number of segments (convergence test)

• Beverages

Traps

• Most programs allow modelling of traps

• Inserted as “Loads”• EZNEC allows for

R+jX form or Laplace transform polynomial

• But see cautions in Cebik and W8JI sites

Beverage modelling

• Exercise in frustration• Ground problems• low height• must use S-N model

• Need RG for Mininec

• Gnd varies with depth• ON4UN model ??• 2-media ground ?

Optimization software

• Yagi Optimizer - Dos? Yo - YO7 etc

• MultiNEC - can take EZNEC (or other) files, and run them, making changes to selected parameters between runs.

Demonstration of EZNEC 3.0

• Using free demo version of EZNEC 3.0

• Model of “Field Day Special” antenna

• Necessarily brief