Re: NEC-LIST:helical ant. modeling

Cornel,
The approximation I have seen most often used is that the modelled
equivalent radius of the strip equals one quarter of the width of the
strip. This is not a theoretically rigorous answer, but it should get you
reasonable results.

I have modelled helicals on NEC2, and the results are an indictment of the
poor theoretical basis for reported helical gains. NEC found an optimum 6
wavelength helix had only about 14 dB circular gain, much less than is
often claimed. The reason seems to be excessive intensity in the sidelobes.
The MINIMUM off-axis intensity was -12db in the centre of the 'nulls', only
26 dB down on the main lobe! Major sidelobes are at -8dB and -14 dB at 30
degrees and 45 degrees off axis. A plethora of other sidelobes reach -20dB
on the main lobe.

Kraus calculated gain by looking at beamwidth, and I think the wasted power
going into the sidelobes gives the lower computed results.

Sincerely,
Trevor Marshall

>Hello ,
>
>I try to model a helical antenna, made of a printed line on a flexible
>substrate that then I roll onto a cylinder.
>Does anybody know of an equivalency "printed line width" - "wire
>diameter", so I can accurately obtain some impedance information?
>
>Thank you,
>Cornel Gazdaru

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