In article , Richard Clark
wrote:
On Thu, 23 Oct 2008 07:01:18 -0400, (J. B. Wood)
wrote:
In article , Richard Clark
wrote:
Lest there be any confusion: an antenna IS a transmission line.
Hello, and I think one would have to include two antennas and the
intervening medium(s) for the above statement to make sense.
...
Over a range
of frequencies the behavior of this 2-port can easily differ from that of
a transmission line, though.
It would appear your first sentence is contested by your last sentence
in your reply.
snip
Hello, Richard, and all. And as I previously pointed out the 2-port model
might not be the equivalent of a line in a broadband sense. Another way
to put it would be that the 2-port could have the electrical
characteristics (characteristic impedance, delay, loss) of a particular
line at one frequency but of a different line at another frequency.
Please excuse my snipping of the remainder of your comments but they sound
more of philosophy than science and quite frankly I have no idea what
you're talking about. You emphatically stated an antenna "IS" a
transmission line without a few words on why this should be so.
My take on a transmission line (or waveguide) is that it is a medium
(ideally lossless) used to convey electromagnetic energy from one place to
another. An antenna (or antenna array) is used to introduce or extract
electromagnetic energy from a medium. Unlike the power available at the
output of a low-loss transmission line, a receiving antenna operating at a
far-field distance from a transmitter can only extract a macimum of 1/2
the power available from an incident electromagnetic wave.
Now, if you meant that antennas and transmission lines share phenomena in
common (e.g. standing waves) that would be a correct statement. And
Maxwell's equations certainly apply to both. But I don't see an
equivalency of a single antenna and a non-radiating (at least intended by
design) transmission line and I don't recall any of my many
electromagnetics texts making such a statement. Sincerely,
What you are arguing is a failure of application, not a failure of the
device. I've seen similar arguments that forced terms of transformer
or transducer into the mix to show how they fail. I find the terms
suitable in a casual discussion, but the new minted failures occur on
the basis of forcing definitions when the casual applications worked
just fine.
One can, by a simple twist of the oscillator's frequency knob, find
failure in all analogues of antennas, lumped circuits, and
transmission lines. Those failures are not exotic perturbations in
the 5th decimal place, but simple and utter refusals to conform to a
general rule (such as my bald statement). For any attempt to refute
my bald statement with "proven concepts" will reveal those challenging
concepts built on a foundation of sand by a similar token of counter
proof.
73's
Richard Clark, KB7QHC
John Wood (Code 5550) e-mail:
Naval Research Laboratory
4555 Overlook Avenue, SW
Washington, DC 20375-5337