resonant antenna [′res·ən·ənt an ′ten·ə]
(electromagnetism)
An antenna for which there is a sharp peak in the power radiated or
intercepted by the antenna at a certain frequency, at which electric
currents in the antenna form a standing-wave pattern.

McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright ©
2003 by The McGraw-Hill Companies, Inc.


I thought a resonant antenna was resistive without any reactance.
Mikek

On Wednesday, August 22, 2012 7:47:07 PM UTC-5, amdx wrote:
I thought a resonant antenna was resistive without any reactance.

Consider a transmission line with standing waves. There is a point every 1/2WL where the impedance is a low "resistance without any reactance". That is the point where the standing wave voltage is in phase with the standing wave current. A 1/2WL dipole is a standing wave antenna with an SWR on the antenna of approximately 20:1. At the center feedpoint, the standing wave voltage is in phase with the standing wave current so the feedpoint impedance is "resistive without any reactance".

If you look at the current and voltage distribution on a standing wave antenna you will find that it looks just like the current and voltage distribution on a transmission line with reflections.

http://www.learn-about-electronics.c...d-voltage.html

http://vsagar.com/2012/02/23/voltage...ipole-antenna/
--
73, Cecil, w5dxp.com

On 08/22/2012 08:47 PM, amdx wrote:
resonant antenna [′res·ən·ənt an ′ten·ə]
(electromagnetism)
An antenna for which there is a sharp peak in the power radiated or
intercepted by the antenna at a certain frequency, at which electric
currents in the antenna form a standing-wave pattern.

McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright ©
2003 by The McGraw-Hill Companies, Inc.


I thought a resonant antenna was resistive without any reactance.
Mikek

Hello, and resonance for an antenna (or any device for that matter)
occurs when the reactive component of the input impedance vanishes. For
a given impressed voltage, the input current is relatively large at
resonance. The definition cited above is completely consistent with
this state (Did you really think something from a McGraw-Hill book
wouldn't be a "proper" definition?)

Now, we also have "antiresonance" in which the reactive component also
vanishes but for a given impressed voltage the input current is
relatively small.

Both resonance and antiresonance occur in antennas (but at different
frequencies). Sincerely, and 73s from N4GGO,

--
J. B. Wood e-mail:

On 8/22/2012 7:47 PM, amdx wrote:
resonant antenna [′res·ən·ənt an ′ten·ə]
(electromagnetism)
An antenna for which there is a sharp peak in the power radiated or
intercepted by the antenna at a certain frequency,

This is not correct.

at which electric
currents in the antenna form a standing-wave pattern.

The standing waves will exist whether resonant or not.

McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright ©
2003 by The McGraw-Hill Companies, Inc.


I thought a resonant antenna was resistive without any reactance.
Mikek

It is resistive *at the feedpoint* when properly made.

John

On Thursday, August 23, 2012 9:36:23 AM UTC-5, John S wrote:
An antenna for which there is a sharp peak in the power radiated or
intercepted by the antenna at a certain frequency,

This is not correct.

At 14.32 MHz a certain dipole accepts 159.2w from a 100v source into a resonant 62.8 ohm feedpoint impedance. At 14.25 MHz, it accepts 160.2w from a 100v source into a non-resonant 61.9-j6 ohm feedpoint impedance. So it appears that you are technically correct but maybe splitting hairs.
--
73, Cecil, w5dxp.com

On Wednesday, August 22, 2012 7:47:07 PM UTC-5, amdx wrote:
resonant antenna [′res·ən·ənt an ′ten·ə] (electromagnetism)
An antenna for which there is a sharp peak in the power radiated or
intercepted by the antenna at a certain frequency, at which electric
currents in the antenna form a standing-wave pattern.

Seems that these conditions would also exist for any conjugately matched non-resonant standing-wave antenna.

On 8/23/2012 3:22 PM, W5DXP wrote:
On Thursday, August 23, 2012 9:36:23 AM UTC-5, John S wrote:
An antenna for which there is a sharp peak in the power radiated or
intercepted by the antenna at a certain frequency,

This is not correct.

At 14.32 MHz a certain dipole accepts 159.2w from a 100v source into a resonant 62.8 ohm feedpoint impedance. At 14.25 MHz, it accepts 160.2w from a 100v source into a non-resonant 61.9-j6 ohm feedpoint impedance. So it appears that you are technically correct but maybe splitting hairs.
--
73, Cecil, w5dxp.com


It does not say "a sharp peak in the power *accepted*" by the antenna.

John

On 8/23/2012 3:22 PM, W5DXP wrote:
On Thursday, August 23, 2012 9:36:23 AM UTC-5, John S wrote:
An antenna for which there is a sharp peak in the power radiated or
intercepted by the antenna at a certain frequency,

This is not correct.

At 14.32 MHz a certain dipole accepts 159.2w from a 100v source into a resonant 62.8 ohm feedpoint impedance. At 14.25 MHz, it accepts 160.2w from a 100v source into a non-resonant 61.9-j6 ohm feedpoint impedance. So it appears that you are technically correct but maybe splitting hairs.
--
73, Cecil, w5dxp.com


You just showed that the off-resonant antenna accepts *more* power than
the resonant one. That is not a "sharp peak."

John

On 8/23/2012 3:22 PM, W5DXP wrote:
On Thursday, August 23, 2012 9:36:23 AM UTC-5, John S wrote:
An antenna for which there is a sharp peak in the power radiated or
intercepted by the antenna at a certain frequency,

This is not correct.

At 14.32 MHz a certain dipole accepts 159.2w from a 100v source into a resonant 62.8 ohm feedpoint impedance. At 14.25 MHz, it accepts 160.2w from a 100v source into a non-resonant 61.9-j6 ohm feedpoint impedance. So it appears that you are technically correct but maybe splitting hairs.
--
73, Cecil, w5dxp.com


You used a fixed 100V source. If you can do that, I can use a fixed 1A
source. In that case a resonant antenna of 62.8 ohms feedpoint
resistance will radiate very nearly 62.8W. An antenna with a feedpoint
impedance of 62.8 + j50 will radiate very near 62.8W.

There is no sharp peak in the power radiated whether at resonance or
not. The definition as it stands is incorrect.

On Friday, August 24, 2012 12:25:23 PM UTC-5, John S wrote:
You used a fixed 100V source.

Let's modify the definition until you agree with it. How about?

resonant antenna [′res·ən·ənt an ′ten·ə] (electromagnetism)
An antenna in which there is a peak in the standing wave energy on the antenna at a certain frequency during receive when configured as an unloaded parasitic element using a constant power, variable frequency source for the incident RF fields.

Would you agree that that energy peak indicates antenna resonance?
--
73, Cecil, w5dxp.com