Current chokes for antenna on a pole

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Pushhead

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Hi all,

My question regards cancelling parasitic currents on an antenna pole.

I would like to mount a discone antenna on a metal-pole. The simulation shows a leakage current on the metal-pole which changes the radiation pattern of the discone antenna. I would like to design a sleeve choke for the pole.

1. Can anyone post comments or references about these current chokes?
2. Is there any suitable solution for wideband antennas as the discone?

Thanks alot,
P.
 

By discone do you mean the type where there are rods in a circle horizontally, and longer rods angled downward? If so, the pole is surrounded by the ground plane of the antenna and a metal pole should not be too much trouble. If you want, extend the antenna a few feet above the metal pole with a short length of fiberglass or pvc.
 

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    Pushhead

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Not a discone made of rods but somthing smaller. Please review the attached picture.

Thanks.
 

That is a small one! Still, mounting the antenna on a smal lengthof insulator before attaching it to the pole should make the pole less of a factor.

How much does the pole actually change the pattern? It should still be symmetrical.
 

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    Pushhead

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THanks for the reply biff44,

My description was not accurate enough i guess.
The setup is a discone (as seen in the picture) and a rigid coax that runs inside the pole and feeds the antenna.
Another possible setup is just a rigid coax (not mounted on a pole).

In both cases the simulation results show that the leakage current magnitude on the pole/coax is ~15 dB below the maximum. This creates a ripple in the radiation pattern (elevation cut) of ~3.5dB peak-to-peak.

My goal is to choke these currents, so the ripple will not exceed 1dB peak-to-peak.

Any ideas?

Thaks again,
P.
 

Would using ferrite material, ala ferrite beads, on the semi-rigid coax help?

BR,
Dave
 

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    Pushhead

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Well, the frequency range is above 2 GHz, so ferrite beads will be transparent as air...

Does anyone know anything about broadband sleeve chokes instead?

Regrdz,
P.
 

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