Re: NEC-LIST: Modeling a resistive loaded dipole

Pascale Lutz wrote:
>
> I am a research student in the Geophysics Laboratory of the
> University of Pau, I work on design of a Ground Penetrating Radar
> antenna.
>
> I would like to model a resistive loaded dipole using NEC-2 and
> obtain in particular the evolution of the Standing-Wave Ratio and
> the efficiency with respect to the frequency. These will go a long
> way in helping me determine the frequency bandwidth with which my
> antenna works.....

Pascale,

I have numerically modelled and measured (but only at a few
frequencies searching for a NVIS antenna) many types of resistance
loaded antennas: travelling wave dipoles (sometimes called the
Australian dipole), terminated dipoles, terminated sloping wire,
sloping V, sloping triangle, half rhombics, and delta antennas.

Calculation of SWR is easy. Look at how the impedance changes with
frequency, and try and choose an optimum resistive load to match to.
Choose this impedance as the source impedance --- I do not know what
programme you are using --- I use EZNEC-Pro.

Finding an optimum antenna is another matter. None of the antennas I
have looked at are very good, unless the travelling wave antenna is
very long/or large a great deal of the power is dissipated in the
resistance loads; and if too large one gets into problems with pattern
at the high frequency end of the band of frequencies of interest ---
directive lobes in directions that are not suitable for the
application.

Regards, Jack, VE2CV

Belrose, J.S., J. Litva, G.E. Moss and E.E. Stevens, "Beverage
Antennas for Amateur Communication", QST, pp. 22-27, January 1983.

Belrose, J.S., "Terminated Folded Dipole", QST (Technical
Correspondence), May 1988, p. 94.

Belrose, J.S., G.M. Royer and L.E. Petrie, "HF Wire Antenna over Real
Ground: Computer Simulation and Measurement", AGARD LS 165, Modern
Antenna Design using Computers and Measurement: Application to Antenna
Problems of Military Interest, Specialized Printing Services Ltd.,
Loughton, Essex, U.K., September 1989 (overview 30 pages).

J.S. Belrose, "Terminated Folded-Dipole", QST (Technical
Correrspondence) May 1994, pp. 88-89.

Belrose, J.S., "On the Travelling-Wave Linear Dipole", QEX June
1994, pp. 22-25.

_____________________________________________
John S. (Jack) Belrose, PhD Cantab, VE2CV
Senior Radioscientist
Radio Sciences Branch
Communications Research Centre
PO Box 11490 Stn. H
OTTAWA ON K2H 8S2
CANADA
TEL 613-998-2779
FAX 613-998-4077
e-mail <john.belrose_at_crc.ca>
_____________________________________________
Received on Mon Mar 27 2000 - 06:15:40 EST