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The meaning of 'Radiation Resistance'
I note some variation in the use of the term 'Radiation Resistance' (Rr)
that suggests that it has different meanings to different folk. One suggestion is that it is the resistance seen by a transmission line connected to an antenna that expresses its coupling to distant regions of space. If that is the case, Rr would not capture energy that is lost in reflection from real ground. So, Rr would be the sum of power in the far field divided by RMS current squared. If indeed it is the "resistance seen by a transmission line", then the current above would be the current at the end of the transmission line. Does the term have an accepted single clear meaning? Is the above correct? 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; - Rr of a half wave folded dipole of equal conductor diameters would be around 300 ohms. Thanks Owen |
The meaning of 'Radiation Resistance'
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." 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. 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, -- John Wood (Code 5520) e-mail: Naval Research Laboratory 4555 Overlook Avenue, SW Washington, DC 20375-5337 |
The meaning of 'Radiation Resistance'
Owen,
I like the IRE definition, which according to W8JI is: "The total power radiated in all directions divided by the square of the net current causing the radiation". That definition draws a distinction between Rrad and the resistive component of the feedpoint impedance; it makes the Rrad of a folded dipole 75 ohms, not 300 ohms; and it avoids some of the errors folk make in assuming that "folding" a vertical can reduce ground losses. 73, Steve G3TXQ |
The meaning of 'Radiation Resistance'
On Jul 15, 3:14*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. One suggestion is that it is the resistance seen by a transmission line * connected to an antenna that expresses its coupling to distant regions of space. If that is the case, Rr would not capture energy that is lost in reflection from real ground. So, Rr would be the sum of power in the far field divided by RMS current squared. If indeed it is the "resistance seen by a transmission line", then the current above would be the current at the end of the transmission line. Does the term have an accepted single clear meaning? Is the above correct? 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; - Rr of a half wave folded dipole of equal conductor diameters would be around 300 ohms. Thanks Owen Owen Can I suggest that you look at things differently? Radiation is created by the acceleration of charge which effectively that which creates an acceleration of a particle such as a bullet from a rifle. The reaction to the firing of the bullet is the recoil which is considered as the resistance to radiation. If you expend energy in other places to get to the point of firing they can only be referred to as losses. Thus radiation is a point vector and should not be confused by multiple vectors that create a plasma. All radiation equations are formed by the use of boundary equations which requires recognition of vectors or point charge and NOT by acceptance of the term "waves." As an illustration, a superconductive material has the minimum resistance possible to ensure the credibility of Ohms law. This resistance has nothing to do with "dc resistance" because current flow is at or near the surface because of the destruction of skin depth resistance phenomina, which also means the cancellation of magnetic fields.( Not destruction as the magnetic field is transformed into a energy bank) Thus ejection of particles can be considered as purely that of the displacement current formed. Expansion of static laws to those of dynamic form establishes the use of particles with the use of boundary laws (vectors) together with conformety with Classical laws. Regards Art |
The meaning of 'Radiation Resistance'
On 7/15/2010 6:43 AM, J.B. Wood 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." Whoops! I meant to say "ratio" vice "radio". Sincerely, and 73s from N4GGO, -- John Wood (Code 5520) e-mail: Naval Research Laboratory 4555 Overlook Avenue, SW Washington, DC 20375-5337 |
The meaning of 'Radiation Resistance'
"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 |
The meaning of 'Radiation Resistance'
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 |
The meaning of 'Radiation Resistance'
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The meaning of 'Radiation Resistance'
Radiation resistance is pretty much what the writer wants it to be.
Consequently, it has to be explicitly each time it's used whenever an ambiguity might arise. It's simply a resistance whose "dissipation" (absorbed power) is the amount radiated. Most writers would probably argue that power lost from the near field to nearby lossy objects such as ground never got radiated, and therefore the corresponding resistance should be considered loss rather than radiation resistance. The presence of nearby ground, however, can also change the value of the remaining resistance due to mutual coupling and alteration of the current distribution, so a particular antenna doesn't have a single inherent value of radiation resistance independent of environment. As for the location where radiation resistance is defined, I believe it's common in AM broadcasting, for example, to refer the radiation resistance of a monopole to a current loop (maximum). If this is a different location than the feed point, the resistance (neglecting loss) at the base will be different from the loop radiation resistance. The ratio of base radiation resistance to loop radiation resistance will in fact equal the square of the ratio of loop current to base current. So radiation resistance measured at the base can be "referred" to the loop by scaling by this ratio. (The power "dissipated" by radiation resistance referred to a loop or any other point has to equal the "dissipation" of the radiation resistance seen at the base or any other point. So Rr has to differ to keep I^2 * Rr constant as Rr is referred to points having different values of I.) The radiation resistance can be referred to any point on the antenna, so the writer has to specify what point is used. But one point is as acceptable as another. It's vital, though, when using radiation resistance, that the current at the defined point is used for calculations. And loss resistance must also be referred to the same point if efficiency calculations are to be made. Some authors, for example Kraus, consistently refer the radiation resistance to the feed point. But Kraus doesn't explicitly apply the term "radiation resistance" to a folded dipole. There's nothing at all wrong, however, with declaring the radiation resistance of a folded dipole to be ~300 ohms. The power radiated is the current measured at the feed point, squared, times that resistance. It's equally legitimate to declare the radiation resistance of a folded dipole to be that of an unfolded equivalent, or ~75 ohms. If you do, though, you also have to work with the current of the unfolded dipole to make the power come out correct. A common mistake when dealing with folded unipoles, made by at least several prominent people who should have known better (and marketing people who probably do know better but find it advantageous to be incorrect), is to refer the radiation resistance to the feed point but the loss resistance to the unfolded equivalent. This results in an erroneous efficiency calculation that incorrectly attributes an improvement due to folding. As I said, you can refer the radiation resistance to either, but if you want to calculate efficiency, you have to refer the loss resistance to the same point and having undergone the same transformation. And when you do, you find that folding fails to produce the often-claimed efficiency improvement. Roy Lewallen, W7EL |
The meaning of 'Radiation Resistance'
Thanks Roy.
I note you observe similar variation in usage as I note. Yes, consistency in an application is more important than a common meaning of the term, but a common meaning of the term assists simpler communication. Regarding say, a base fed folded monopole and efficiency calculations, if the connection to ground is though of as having some actual value Rg, since the current flowing in Rg is twice the feedpoint current, consistent development of the circuit model will reveal the correct efficiency as: Rr/(Rr+2Rg) where Rr is the sum of power in the far field divided by feed point current squared. You don't need to fudge Rr to get the result, proper allowance of the power due to the actual current in Rg provides the correct result. Kraus (Annennas for All Applications) effectively defines Rr as part of his development of the concept of a pair of conductors transitioning from a non-radiating transmission line to an antenna to free space radiation. He does say "... the radiation resistance Rr, may be thought of as a "virtual" resistance that does not exist physically but is a quantity coupling the antenna to distant regions of space via a "virtual" transmission line." It is his use of "distant regions of space" that suggests in the case of ground reflection, it is the remaining total power in distant free space after lossy reflection that is used to calculate Rr. The power lost in reflection would be a component of feed point R, but not Rr. He also states a little earlier "... the antenna appears to the transmission line as a resistance, Rr, called the *radiation resistance*. It is not related to any in the antenna itself, but a resistance coupled to the from space to the antenna terminals." This seems fairly clear to me that he defines radiation resistance to be at the transmission line / antenna interface. Both of these statements by Kraus are simple, but would seem to be capable of application to real antenna systems. I can't immediately think of exceptions (game on???). In Kraus's language, ground reflections might reasonable be considered part of the 'antenna' since they influence its pattern and loss, and loss in the ground reflections is due to resistance "in the 'antenna' itself" and so excluded from Rr. Is there anything in Kraus's statements that is wrong, or my interpretatiohn of them. Owen |
The meaning of 'Radiation Resistance'
Owen Duffy wrote in
: .... If I take a half wave folded dipole immersed in some environment where the ambient noise temperature is T, and attach a load directly to the feedpoint, the load power will be maximum when it is about 300 ohms rather than about 75 ohms, and the noise power density due to ambient noise would be K*T*300 W/Hz rather than K*T*75 W/Hz. If Rr is the (virtual) resistance due to coupling of the antenna with distant space, then surely this example suggests that Rr is 300 rather than 75 ohms. (If I performed the same experiment with a plain half wave dipole, the load power will be maximum when it is about 75 ohms, and the noise power density due to ambient noise would be K*T*75 W/Hz.) Sorry, that is plainly wrong. Clarity struck whilst having breakfast, the received power of a matched system should be independent of R. Noise power density is simply K*T W/Hz. There is no R term. The text should read... If I take a half wave folded dipole immersed in some environment where the ambient noise temperature is T, and attach a load directly to the feedpoint, the load power (due to ambient noise) will be maximum when it is about 300 ohms rather than about 75 ohms. If Rr is the (virtual) resistance due to coupling of the antenna with distant space, then surely this example suggests that Rr is 300 rather than 75 ohms. My apologies. Owen |
The meaning of 'Radiation Resistance'
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 |
The meaning of 'Radiation Resistance'
Owen Duffy wrote:
Thanks Roy. I note you observe similar variation in usage as I note. Yes, consistency in an application is more important than a common meaning of the term, but a common meaning of the term assists simpler communication. True. But we can't force consistency of a term that's already ubiquitous in the literature with a variety of meanings. Saying it's so doesn't make it so. Regarding say, a base fed folded monopole and efficiency calculations, if the connection to ground is though of as having some actual value Rg, since the current flowing in Rg is twice the feedpoint current, consistent development of the circuit model will reveal the correct efficiency as: Rr/(Rr+2Rg) where Rr is the sum of power in the far field divided by feed point current squared. You don't need to fudge Rr to get the result, proper allowance of the power due to the actual current in Rg provides the correct result. Ok, here we go. Remember that efficiency is really a power ratio, not a resistance ratio. It reduces to the familiar resistance formula only when the currents in both radiation and loss resistances are the same. Let's talk about Rg. An unfolded monopole has a single connection to ground, and we can call this resistance Rg. If Rr is the base radiation resistance, then the same current flows through Rr and Rg, so efficiency = Pr/(Pr + Pg) = Rr/(Rr + Rg) and everything's fine. But when we fold it, there are two connections to ground -- the "cold" side of the feedline and the non-feed monopole conductor. Each has half the original current. The "hot" side of the feedline carries the same current as the "cold" side so its current is half the original value also. You have your choice for Rg -- you can consider it to be the original ground system resistance but with twice the current flowing through it as through the feedpoint resistance; or you can split the original into two equal parallel resistances of twice the value, each with the same current as at the feedpoint. In the first case, you get the equation you posted. In the second, you get Rr/(Rr + Rg). We've basically referred the ground resistance to the transformed feedpoint. The surest way to stay out of trouble is to always calculate efficiency as a ratio of powers. If you use I^2 * R for radiation power and loss power, you can't go wrong, regardless of where you choose either R to be, as long as the I is at the same point. Kraus (Annennas for All Applications) effectively defines Rr as part of his development of the concept of a pair of conductors transitioning from a non-radiating transmission line to an antenna to free space radiation. He does say "... the radiation resistance Rr, may be thought of as a "virtual" resistance that does not exist physically but is a quantity coupling the antenna to distant regions of space via a "virtual" transmission line." It is his use of "distant regions of space" that suggests in the case of ground reflection, it is the remaining total power in distant free space after lossy reflection that is used to calculate Rr. The power lost in reflection would be a component of feed point R, but not Rr. Well, we can get carried away with this, too. Nearby ground sucks power from the near field and that power is never radiated. The longer distance ground reflection primarily responsible for elevation pattern development uses power which has been radiated from the antenna conductor(s). Is that reflection "distant"? When you calculate an antenna's efficiency, do you include the power radiated from the conductor before or after the ground reflection? What about power that's lost by radiation to space? It's just as surely lost for terrestrial communication as power warming the ground. Answer: It's entirely up to you. You could even consider all energy which doesn't strike your receiving antenna as "loss". All you have to do is clearly state what you're including and what you're not. He also states a little earlier "... the antenna appears to the transmission line as a resistance, Rr, called the *radiation resistance*. It is not related to any in the antenna itself, but a resistance coupled to the from space to the antenna terminals." This seems fairly clear to me that he defines radiation resistance to be at the transmission line / antenna interface. Kraus is consistent with this, but other respected authors use the term radiation resistance differently. The few who use the term radiation resistance when lossy ground is present, though, seem to regard near-field coupling loss to ground as loss, and not consider far field reflection in efficiency calculations at all. Both of these statements by Kraus are simple, but would seem to be capable of application to real antenna systems. I can't immediately think of exceptions (game on???). As I said above, how distant? In Kraus's language, ground reflections might reasonable be considered part of the 'antenna' since they influence its pattern and loss, and loss in the ground reflections is due to resistance "in the 'antenna' itself" and so excluded from Rr. Is there anything in Kraus's statements that is wrong, or my interpretatiohn of them. Owen Kraus isn't wrong. Neither are the other respected authors who use the term differently. I'm sorry, but you're looking for something that doesn't exist, and I don't see the point in trying to invent a strict definition just for your own use. Roy Lewallen, W7EL |
The meaning of 'Radiation Resistance'
Owen Duffy wrote in
: Rr/(Rr+2Rg) That should have an exponent in the Rr/(Rr+2^2Rg) |
The meaning of 'Radiation Resistance'
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 |
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