Re: NEC-LIST: Re: Plasma Antennas

Hello,

> Recapping I guess these are the most obvious aspects of plasma antennas
> (please add/correct/delete& trying to get a complete picture of the
> technology here!):
>
> Plasma is simply a replacement for metal as a conductor. Plasma antennas
> come in different shapes: reflectors, direct radiators, lenses.
>
> Pros:
> · Plasma is only required when using antenna, default could be off:
> transparent tube (plasma container) remains with negligable conductivity.
> · Possibly aerial is lighter than metal one.
> · By tapering (or stepping) the cross-section of the plasma container,
> the length of the antenna can be varied by increasing or decreasing the
> plasma creating current. Combined with tapered helical or spiral
> arrangement, this leads to varying beamwidth and/or bandwidth.
> · Many forms of plasma container possible (even inflatable claimed).

add :
· Potential stealth application (reduced radar cross section when the plasma is turned off)

> Cons:
> · Energised plasma creates wideband noise (which does not have to be a
> problem for high power transmitters; and Markland claims there is
> virtually no noise when gas is ionised).
> · Energy required to establish and maintain plasma.
> · Plasma has a very high temperature.
> · Probably entire system is more expensive, more complex, more damage
> prone and heavier than comparable metal antenna.
> · Low radiating efficiency (order 50%-70%, although 1%-5% also claimed).

add :

· Non-linear behavious of plasma

I personally witnessed these phenomena during my undergraduate days
when I was employed in a microwave research lab at the École Polytechnique
de Montréal. One of the groups was working in the field of antennas
immersed in plasma. The plasma not only generated harmonics, but also
very strong sub-harmonics (comparable to the fundamental) under certain
conditions. The latter apparently stemmed from the interaction in the contact
area between the plasma sheath and the metallic monopole. The propagation
speed was also slower on the outer surface of the plasma than on the monopole.

I therefore believe that the possibility of linearity problems should at least
be considered or investigated in "pure" plasma antennas.

Nota bene : I wasn't a researcher (ie, a poor graduate student toiling over the
vacuum pump), so I'm not intimately familiar with the plasma physics. However,
I did have some involvement.

Alexandre

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