On Fri, 28 Jul 2006 23:25:10 -0400, jawod wrote:

Dave wrote:
well, 'adaptive beamforming' is two words...

'beamforming' means forming a directional 'beam' using an antenna. be it a
simple parasitic array like yagi's or a complex array of driven elements
like a flat panel radar.
....
'adaptive' means forming the beam in a way that makes it work better in the
environment, or adapt to it's surroundings.
....
Given the need for "stealth" antennas, Is there /are there design(s)
that create small footprint antennas that function as larger traditional
ones?

Can a longwire be divided into small segments that are independently
controlled such that the sum of the parts behave differently than the
whole?...and can this effect be altered via software?

Has anyone been working on this approach?

Hi John,

As David and others offer, this adaptability and beamforming
characteristic is a product of both massive duplication and a large
area with respect to the wavelength of interest. To put it in rather
more traditional terms:
"There's no such thing as a free lunch."

You ask about controlling small segments independently. Can you
imagine that this maze of control wires would in itself be a more
capable antenna? This is the price of complexity: if you can afford
these elaborations in design, why not do it the traditional way? You
gain nothing in sensitivity, you gain nothing in efficiency (which is
most certainly the first characteristic to suffer by orders of
magnitude). And to offer it as a prospective "stealth" antenna is
defeated from the outset.

Think of a rather more practical example that is also a good metaphor.
Imagine the Fresnel lens. It performs its beamforming through
segmentation. Its advantage is that it is lighter than the complete
lens, but if you can tolerate the weight, it offers nothing else to
compensate for the elaboration of a complex set of lens segments piled
one atop the other.

Now, if you can pay the price of elaboration, you can spread antenna
elements about - disguised even. You can bury control cables and
signal cables - you will certainly need them both. You can devise a
control program to "focus" the antenna - which is what beamforming is
all about. OR you can twist knobs like the thousand armed Shiva to
achieve the same thing. For some, this technical challenge alone is
worth the struggle - forget the DX. And yes, you will actually gain
an advantage over a single fixed antenna.

Try with the four square antenna which encompasses all these topics
that interest you. If you can wrestle with the knots of its
complexity, you can step up to more sophisticated issues.

73's
Richard Clark, KB7QHC