| Home |
| Search |
| Today's Posts |
|
#15
October 24th 08, 12:16 PM
posted to rec.radio.amateur.antenna
|
|||
|
|||
Antenna design question
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 |
| Thread Tools | Search this Thread |
| Display Modes | |
|
|
Similar Threads
|
||||
| Thread | Forum | |||
| dipole antenna design question | Antenna | |||
| Amp design question | Homebrew | |||
| Yagi antenna design question | Antenna | |||
| Question about the uses for an antenna design | Antenna | |||
| Ferrite Magnet antenna ; parts purchase / design question | Shortwave | |||
Threaded Mode
