"J.B. Wood" wrote in news:i1monr$2od$1
@ra.nrl.navy.mil:

On 07/15/2010 04:14 AM, Owen Duffy wrote:
I note some variation in the use of the term 'Radiation Resistance' (Rr)
that suggests that it has different meanings to different folk.

snip
Hello, and I don't find any ambiguities in any of my various EM and
antenna theory textbooks. FWIW, from the IEEE Standard Dictionary of
Electrical and Electronics Terms:

"Radiation resistance (antenna). The radio of the power radiated by an
antenna to the square of the rms antenna current referred to a specified
point. Note: This term is of limited utility in lossy media."


Hmmm. The last statement suggests that, as defined, it is not clear and
unambiguous in the real world because the real world involves "lossy
media".

The "reference to a specified point" suggests that if one gives a value for
Rr, it is necessary to also state the reference point. Is that what it
means?

This is exactly the lack of clarity that is troubling me.

So if we're looking at free (in vacuo) space the radiation resistance is
simply a "load" resistance component that accounts for where the
radiated power goes. The radiation resistance doesn't include any other
resistive losses in the antenna structure/proximity operating
environment that may also be dissipating source power introduced at the
feedpoint of the antenna.

This does not address the issue of ground reflection that I mentioned.

An aerodynamic analogy would be the
distinction between "induced" drag (the price paid for "lift") and
"parasite" drag, which are both components of the total drag.
Sincerely, and 73s from N4GGO,

I am not an aerodynamics type, so drawing that analolgy only helps to
confuse. You might as well use optics!

I know you are trying to be helpful John, but the IREE definition doesn't
seem to clarify the issue.

To put some numbers on my first example, if I have an NEC model of a centre
fed half wave dipole with zero conductor losses, mounted over real (ie
lossy) ground, and feedpoint R at resonance is say, 60 ohms, and total
power in the *far field* divided by I^2 is say, 50 ohms, is Rr 50 ohms? Is
the power "radiated" from such a dipole ONLY the power that makes it to
'distant space', or is radiated power input power less dipole conductor
losses?

The IREE definition suggests that I need also to state that Rr is 50 ohms
at the centre, and the term is is of "limited utility" (not unambiguously
clear?) because of the lossy ground reflections.

If indeed the term Radiation Resistance is only applicable in lossless
scenarios as suggested by the IREE dictionary, what it a clear and
unambiguous language for the real world?

Cheers
Owen

On Thu, 15 Jul 2010 20:01:57 GMT, Owen Duffy wrote:

"Radiation resistance (antenna). The radio of the power radiated by an
antenna to the square of the rms antenna current referred to a specified
point. Note: This term is of limited utility in lossy media."


Hmmm. The last statement suggests that, as defined, it is not clear and
unambiguous in the real world because the real world involves "lossy
media".

Hi Owen,

All of this neatly fits into Broadcast Band transmission where the
current pulse (we are now into the shadow zone of SWR) occurs at the
feedpoint of an antenna that is conventionally a quarter wave tall,
the current can be measured, and the far field power is known. The
matter of "lossy media" has been studied (BL&E) and that variable
reduced by good engineering practices (which brings us back to the
known far field power).

The "reference to a specified point" suggests that if one gives a value for
Rr, it is necessary to also state the reference point. Is that what it
means?

The "reference" is typically the current node. It gets messier with
more complex antenna design.

This is exactly the lack of clarity that is troubling me.

This implies the more complex designs following (or not following)
what you reject as "rules of thumb." Or at least their appearance.
I'm sure there are long and elaborate academic treatises that explain
the current node current measurement in relation to the known radiated
power. I haven't read any of them that I can glibly quote here.

This does not address the issue of ground reflection that I mentioned.

I will return to your original and comment to that:
Some implications of the above are that:
- Rr of a horizontal half wave dipole with zero conductor loss, above
real ground, would have Rr less than R at the feedpoint by virtue of some
loss in waves reflected from real ground;

There are two mechanisms hiding in one description. The ground is
lossy - period. The ground is reflective - period. These are two
different issues in regard to radiation resistance. The Rr is not
ground loss although the measure of Rr may be corrupted by Rground.
That is a problem of separating out the variables. Others have
described that. The reflection from ground may upset the measure of
Rr as well, but if that does not upset the total power, and the
current node can be measured, then you still have a way to quantify
Rr.

- Rr of a half wave folded dipole of equal conductor diameters would be
around 300 ohms.

I thought someone else preceded this discussion with Tom's
explanation. Maybe it went unread, or unrealized. So, in other
words: A folded dipole/monopole is a current transformer. That
transformation ratio is driven, in large part, by the ratio of the
diamters of the conductors. You have acknowledged as much in your own
specification of equal sized conductors. Having said that, the
transformer is also transforming the Z of the load (Rr + Rground) by a
square law. The usual sense of current node has been lost in a more
elaborate design, but the transformation of it returns us to the usual
Rr.

73's
Richard Clark, KB7QHC

On Jul 15, 3:01*pm, Owen Duffy wrote:
"J.B. Wood" wrote in news:i1monr$2od$1
@ra.nrl.navy.mil:

On 07/15/2010 04:14 AM, Owen Duffy wrote:
I note some variation in the use of the term 'Radiation Resistance' (Rr)
that suggests that it has different meanings to different folk.

snip
Hello, and I don't find any ambiguities in any of my various EM and
antenna theory textbooks. *FWIW, from the IEEE Standard Dictionary of
Electrical and Electronics Terms:

"Radiation resistance (antenna). The radio of the power radiated by an
antenna to the square of the rms antenna current referred to a specified
point. *Note: *This term is of limited utility in lossy media."

Hmmm. The last statement suggests that, as defined, it is not clear and
unambiguous in the real world because the real world involves "lossy
media".

The "reference to a specified point" suggests that if one gives a value for
Rr, it is necessary to also state the reference point. Is that what it
means?

This is exactly the lack of clarity that is troubling me.

So if we're looking at free (in vacuo) space the radiation resistance is
simply a "load" resistance component that accounts for where the
radiated power goes. *The radiation resistance doesn't include any other
resistive losses in the antenna structure/proximity operating
environment that may also be dissipating source power introduced at the
feedpoint of the antenna.

This does not address the issue of ground reflection that I mentioned.

*An aerodynamic analogy would be the
distinction between "induced" drag (the price paid for "lift") and
"parasite" drag, which are both components of the total drag.
Sincerely, and 73s from N4GGO,

I am not an aerodynamics type, so drawing that analolgy only helps to
confuse. You might as well use optics!

I know you are trying to be helpful John, but the IREE definition doesn't
seem to clarify the issue.

To put some numbers on my first example, if I have an NEC model of a centre
fed half wave dipole with zero conductor losses, mounted over real (ie
lossy) ground, and feedpoint R at resonance is say, 60 ohms, and total
power in the *far field* divided by I^2 is say, 50 ohms, is Rr 50 ohms? Is
the power "radiated" from such a dipole ONLY the power that makes it to
'distant space', or is radiated power input power less dipole conductor
losses?

The IREE definition suggests that I need also to state that Rr is 50 ohms
at the centre, and the term is is of "limited utility" (not unambiguously
clear?) because of the lossy ground reflections.

If indeed the term Radiation Resistance is only applicable in lossless
scenarios as suggested by the IREE dictionary, what it a clear and
unambiguous language for the real world?

Cheers
Owen

In real world terms radiation resistance is measured by the vector
that overcomes radiation resistance or the conveyance of
communication. This compels the measurement of that which is
accelerated as it is an action and reaction type vector. If one
doesn't have a measurement of the mass that is being accelerated then
radiation resistance itself cannot be supplied. What happens
to the accellerated mass has no connection what so ever to the
accelleration vector.To find the accelerating vector one must first
determine the efficiency of the apparatus used and this will vary
dependent on the method used to produce the accelerating vector so
that one can determine the losses. So if we cannot identify that
vector which creates acceleration of charge where the charge is the
measurement of radiation one must first determine what creates
radiation so that the radiation unit can be measured. The bottom line
is
that one must use a superconductor where only the accelerating vector
comprises of the impedance
seen by the time varying current and where the
resistance of the radiating member is divorced from the equation as is
coupling losses in the absence of a magnetic field.
Art

On 07/15/2010 04:01 PM, Owen Duffy wrote:

"Radiation resistance (antenna). The radio of the power radiated by an
antenna to the square of the rms antenna current referred to a specified
point. Note: This term is of limited utility in lossy media."


Hmmm. The last statement suggests that, as defined, it is not clear and
unambiguous in the real world because the real world involves "lossy
media".


Lossy media is that which absorbs radiation passing through it. IOW it
heats up. This is different than say the outside air being warmed
through conduction from the earth's surface being in turn heated up by
radiation from the sun.

The "reference to a specified point" suggests that if one gives a value for
Rr, it is necessary to also state the reference point. Is that what it
means?

Hello, and yes, you would have to specify where the quantity applies. Rr
is being calculated as I^2 * Rr = Power radiated. The usual reference
point is the feedpoint of the antenna. Note that the antenna feedpoint
could also be defined to include matching networks and even transmission
line. Of course if these other components also radiate they contribute
to the antenna's radiated power.



This is exactly the lack of clarity that is troubling me.

So if we're looking at free (in vacuo) space the radiation resistance is
simply a "load" resistance component that accounts for where the
radiated power goes. The radiation resistance doesn't include any other
resistive losses in the antenna structure/proximity operating
environment that may also be dissipating source power introduced at the
feedpoint of the antenna.

This does not address the issue of ground reflection that I mentioned.


It doesn't matter to the definition of Rr what other agencies may modify
an antenna's characteristics. For example, we measure (at a particular
frequency) the real (resistive) part of its feedpoint impedance. A
portion of that resistance is due to ohmic losses in the earth, antenna
structure, and any other items forward of the feedpoint. The remainder
of the resistance is Rr. In this example the "antenna" consists of the
monopole and its near-field operating environment.

An aerodynamic analogy would be the
distinction between "induced" drag (the price paid for "lift") and
"parasite" drag, which are both components of the total drag.
Sincerely, and 73s from N4GGO,

I am not an aerodynamics type, so drawing that analolgy only helps to
confuse. You might as well use optics!

I know you are trying to be helpful John, but the IREE definition doesn't
seem to clarify the issue.

Well, I've spent a great deal my professional career as an EE dealing
with USN shipboard antennas and just happen to have ham radio as an
"office" related hobby. As I said in my previous post I don't have a
problem with what Rr means. It seems like a rather straightforward and
simple concept. I think you're trying to read more into it then is there.


To put some numbers on my first example, if I have an NEC model of a centre
fed half wave dipole with zero conductor losses, mounted over real (ie
lossy) ground, and feedpoint R at resonance is say, 60 ohms, and total
power in the *far field* divided by I^2 is say, 50 ohms, is Rr 50 ohms? Is
the power "radiated" from such a dipole ONLY the power that makes it to
'distant space', or is radiated power input power less dipole conductor
losses?


The radiated (far field) power is what is relevant to Rr. The radiated
power is the power accepted by the antenna designated feedpoint less the
other ohmic (items that are dissipating heat) losses forward of the
antenna feed and in its (near field) vicinity. Also, by "accepted"
power I mean the actual power into the antenna terminals (incident power
less reflected power).

The IREE definition suggests that I need also to state that Rr is 50 ohms
at the centre, and the term is is of "limited utility" (not unambiguously
clear?) because of the lossy ground reflections.


No it doesn't.


If indeed the term Radiation Resistance is only applicable in lossless
scenarios as suggested by the IREE dictionary, what it a clear and
unambiguous language for the real world?

Cheers
Owen

The definition doesn't say that (cf the word "limited"). Again I think
you're trying to read items, that while possibility contributing to the
measured/calculated Rr value are irrelevant to the basic definition.
IOW those other items such as earth grounds if present really ARE part
of the antenna. The power radiated by the antenna could propagate as
ground wave, sky wave or in combination - it doesn't matter. Sincerely,
and 73s from N4GGO,

--
John Wood (Code 5520) e-mail:

Naval Research Laboratory
4555 Overlook Avenue, SW
Washington, DC 20375-5337