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Old December 22nd 06, 06:44 PM posted to rec.radio.amateur.antenna
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Default Image theory

But the academic books on Antenna theory written by Professors of
Electromagnetics all use image theory for vertical monopole antennas
including those with elevated radials. Can anyone quote an antenna theory
book that does not?


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Old December 22nd 06, 07:08 PM posted to rec.radio.amateur.antenna
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Default Image theory

On Fri, 22 Dec 2006 17:44:41 -0000, "David" nospam@nospam wrote:

But the academic books on Antenna theory written by Professors of
Electromagnetics all use image theory for vertical monopole antennas
including those with elevated radials. Can anyone quote an antenna theory
book that does not?


Hi David,

The objection arises out of your commingling radials in the discussion
where the dons never asserted an image theory for them. Can you quote
any source that does? (Let's try proving a positive.)

73's
Richard Clark, KB7QHC
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Old December 22nd 06, 07:36 PM posted to rec.radio.amateur.antenna
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Default Image theory

On Fri, 22 Dec 2006 10:08:03 -0800, Richard Clark
wrote:

On Fri, 22 Dec 2006 17:44:41 -0000, "David" nospam@nospam wrote:

But the academic books on Antenna theory written by Professors of
Electromagnetics all use image theory for vertical monopole antennas
including those with elevated radials. Can anyone quote an antenna theory
book that does not?


Hi David,

The objection arises out of your commingling radials in the discussion
where the dons never asserted an image theory for them. Can you quote
any source that does? (Let's try proving a positive.)


Let's just cut to the chase, vis-a-vis radials. These elements serve
to balance and match, not to propagate (in the sense of ground
reflections). In fact, when all the radiative contributions of a
ground plane (radials in a plane) are considered, they are self
negating.

If we were to consider the aspect of this image theory (reflection of
a wave); then those radials would have to consume both a lot of
distance out from the feed point, and a lot of real estate. By any
standards found in the market place, or in implementation, this is so
rare as to be exceedingly exceptional. Commercial AM antenna radial
fields DO NOT come close to this either.

73's
Richard Clark, KB7QHC
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Old December 22nd 06, 08:57 PM posted to rec.radio.amateur.antenna
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Default Image theory

David wrote:
But the academic books on Antenna theory written by Professors of
Electromagnetics all use image theory for vertical monopole antennas
including those with elevated radials. Can anyone quote an antenna theory
book that does not?


Kraus, _Antennas_
Johnson, _Antenna Engineering Handbook_
Lo and Lee, _Antenna Handbook_
Balanis, _Antenna Theory_
King and Harrison, _Antennas and Waves_
Jordan & Balmain, _Elecromagnetic Waves and Radiating Systems_
King, Mimno, and Wing, _Transmission Lines, Antennas, and Wave Guides_
Brown, Sharpe, Hughes, and Post, _Lines, Waves, and Antennas_
Stutzman & Thiele, _Antenna Theory and Design_

to name a few. I'm sure there are many more, but those are the ones
currently on my shelf.

Several of these authors use an image to analyze a vertical antenna over
a perfectly conducting ground of infinite extent. None use it for any
other situation, including elevated radials. And for a very good reason
-- it's not valid for other situations.

Roy Lewallen, W7EL
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Old January 7th 07, 08:17 PM posted to rec.radio.amateur.antenna
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Default Followon to image theory

Various books claim that a ground plane reflects the radio wave emitted by
the vertical, and then claim that a ground plane is formed or simulated by
four elevated radials.
I emailed two Professors of antenna theory about this.

Reply from Professor Constantine Balanis:
"The radials should act more as a ground plane. Four of them are usually the
minimum. The more of them, the better the ground plane. The objective of the
ground plane is to reflect the energy from the main element; the vertical
wire".

Reply from Professor Vincent Fusco:
"My view would be that the radials form an image plane, the radials
themselves do not radiate".

The following link on Navy Training Series show the radials as reflecting
the radio wave and forming an image antenna:
http://www.tpub.com/content/neets/14.../14182_219.htm

Quotations from books below.

Antenna Theory third edition by C.A. Balanis page 205 "Improvements in the
efficiency can be
obtained by placing radial wires or metallic disks on the ground. [New
paragragh] The analytical procedures that are introduced to examine the
ground effects are based on the geometrical optics models of the previous
sections. The image (virtual) source is again placed a distance h below the
interface to account for the reflection."

Antenna Theory third edition by C.A. Balanis page 511 "To reduce the wind
resistance, to simplify the design, and to minimise the costs, a ground
plane is often simulated, especially at low frequencies, by crossed wires as
shown in Figure 9.11(b). Usually only two crossed wires (four radials) are
employed. A larger number of radials results in a better simulation of the
ground plane."

Antenna Theory and Design by Stutzman and Thiele page 198: "A ground plane
can take many forms, such as radial wires around a monopole, the roof of a
car, or the real earth....The pattern of an antenna over a real earth is
different from the pattern when the antenna is operated over a perfect
ground plane. Approximate patterns can be obtained by using image theory.
The same principles discussed in Sec 2.3.1 for images in perfect ground
planes apply, except that the strength of the image in a real ground will be
reduced from that of the perfect ground plane case".

Antenna Theory and Design by Stutzman and Thiele pages 66 & 67: "The
principles of image theory are illustrated in this section with several
forms of the monopole antenna. ... Figure 2-12(c) Practical monopole
antenna with radial wires to simulate a ground plane".

Antennas for all applications third edition by J.D. Kraus page 719: "In Fig
21-9d the solid-sheet ground plane is replaced by 4 radial conductors. Fig
21-9(d) stub antenna with 4 radial conductors to simulate a ground plane".

Antenna Engineering Handbook by R.C. Johnson page 110: "The geometrical
shape of a sleeve antenna, or a sleeve monopole, is sketched in Fig. 4-22a.
If the image of the structure is included, then we have a sleeve dipole as
shown in Fig. 4-22b". Figure 4-22a shows a coax cable with the centre wire
going upwards forming a vertical element, and the braid being connected to a
ground plane. Fig 4-22b appears to show a dipole being formed from a
monopole and its image antenna.

Foundations of Antenna Theory and Techniqes by Professor Vincent Fusco pages
190 and 191. Claims that image theory i.e. image cancellation applies to the
horizontal section of an inverted L antenna. The vertical part of inverted L
antenna is a short monopole i.e. less than a quarterwave long.

However references against this are below.
Antenna Engineering Handbook by R.C. Johnson page 118: "When the ground
plane is of finite size, the image theorem does not apply."

Professor Douglas Miron in his book Small Antenna Design says that the
vertical element is driven against some horizontal elements. The horizontal
elements have canceling fields. He says that the radials are an artificial
ground called a counterpoise that also radiates.

Various books also say about using image theory to analyse corner reflector
antennas.

RF experts appear to disagree with each other over the vertical monopole
with quarterwave radials - Roy Lewallen and Professor Douglas Miron versus
Professor Constantine Balanis and Professor Vincent Fusco.












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Old January 7th 07, 09:00 PM posted to rec.radio.amateur.antenna
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Default Followon to image theory

David wrote:
RF experts appear to disagree with each other over the vertical monopole
with quarterwave radials - Roy Lewallen and Professor Douglas Miron versus
Professor Constantine Balanis and Professor Vincent Fusco.


Exactly what is it upon which you think Roy Lewallen
and Constantine Balanis disagree?
--
73, Cecil http://www.w5dxp.com
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Old January 7th 07, 09:24 PM posted to rec.radio.amateur.antenna
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Default Followon to image theory

David wrote:
Various books claim that a ground plane reflects the radio wave emitted by
the vertical, and then claim that a ground plane is formed or simulated by
four elevated radials.


[big snip]

David,

The images in these cases are not real. That's why they are called
virtual. However, real or not, these images can provide useful
assistance in simple determination of the expected radiation patterns.
Like most models, the image model has limitations. Some applications
will succumb to image modeling more readily than others.

Bottom line: There is no real conflict among the experts. Image modeling
is generally quite easy. If the results make sense, be happy. If not,
then try more complex methods. I would expect all of the experts to
agree that detailed mathematical modeling is required for the best
accuracy unless the image model has unrealistic parameters such as
infinite extent, perfect conductivity, etc.

73,
Gene
W4SZ
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Old January 7th 07, 09:41 PM posted to rec.radio.amateur.antenna
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Default Followon to image theory

On Sun, 7 Jan 2007 19:17:55 -0000, "David" nospam@nospam wrote:

Various books claim that a ground plane reflects the radio wave emitted by
the vertical, and then claim that a ground plane is formed or simulated by
four elevated radials.
I emailed two Professors of antenna theory about this.

Reply from Professor Constantine Balanis:
"The radials should act more as a ground plane. Four of them are usually the
minimum. The more of them, the better the ground plane. The objective of the
ground plane is to reflect the energy from the main element; the vertical
wire".


Hi David,

This is becoming tiresome by half.

"Quotes" that do not have a context (what was the question asked?) are
more name dropping than an informed discussion. It is also called
shopping for testimony.

"Does a ground plane reflect?" This is a loaded question much like
"Have the Republicans offered a balanced budget?" Each question can
be so heavily qualified as to guarantee success and bragging rights.
Each can be so heavily doped up on the narcotic of self-indulgence as
to offer only the prospects of a somnambulistic nod of affirmation.

If one conspired to erect a 2M vertical on the radial field of a
former AM station; then, yes, these radials reflect admirably. If one
takes the same 2M vertical (as shipped from, say, Comet) and looked at
the reflection components of its radials; then, yes, these radials
reflects, but with less than pedestrian results. Difference is found
in the application. The AM station ground field will produce more 2M
reflection contacts to the horizon, the standard radials of a 2M Comet
will have indifferent reflection contacts oriented towards satellites.

Simple modeling and analysis reveals this in less than an hour's work.

More effort in the field confirms the modeling and analysis.

Modeling and analysis conform to every expectation offered by all the
authors quoted, given they use the same tools and were, perhaps,
instrumental in their development.

The "Image" theory relates to reflections found in the far field
beyond the physical extent of practical radials. To force the
standard implementations of radials into supporting this theory (to
the exclusion of the greater application), debases the intent of the
theory. Actually, to call it a theory is painting the rose and
gilding the lily. This tarted up observation is used mainly to soothe
the troubled minds of neophytes until they become accustomed to
dealing with larger, more involved problems. It is a suitable
metaphor; however, metaphors are the weakest form of argument as they
often fail early on close examination.

73's
Richard Clark, KB7QHC
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Old January 7th 07, 11:54 PM posted to rec.radio.amateur.antenna
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Default Followon to image theory

David wrote:
Various books claim that a ground plane reflects the radio wave emitted by
the vertical, and then claim that a ground plane is formed or simulated by
four elevated radials.
I emailed two Professors of antenna theory about this.

Reply from Professor Constantine Balanis:
"The radials should act more as a ground plane. Four of them are usually the
minimum. The more of them, the better the ground plane. The objective of the
ground plane is to reflect the energy from the main element; the vertical
wire".

Reply from Professor Vincent Fusco:
"My view would be that the radials form an image plane, the radials
themselves do not radiate".

The following link on Navy Training Series show the radials as reflecting
the radio wave and forming an image antenna:
http://www.tpub.com/content/neets/14.../14182_219.htm

Quotations from books below.

Antenna Theory third edition by C.A. Balanis page 205 "Improvements in the
efficiency can be
obtained by placing radial wires or metallic disks on the ground. [New
paragragh] The analytical procedures that are introduced to examine the
ground effects are based on the geometrical optics models of the previous
sections. The image (virtual) source is again placed a distance h below the
interface to account for the reflection."

Antenna Theory third edition by C.A. Balanis page 511 "To reduce the wind
resistance, to simplify the design, and to minimise the costs, a ground
plane is often simulated, especially at low frequencies, by crossed wires as
shown in Figure 9.11(b). Usually only two crossed wires (four radials) are
employed. A larger number of radials results in a better simulation of the
ground plane."

Antenna Theory and Design by Stutzman and Thiele page 198: "A ground plane
can take many forms, such as radial wires around a monopole, the roof of a
car, or the real earth....The pattern of an antenna over a real earth is
different from the pattern when the antenna is operated over a perfect
ground plane. Approximate patterns can be obtained by using image theory.
The same principles discussed in Sec 2.3.1 for images in perfect ground
planes apply, except that the strength of the image in a real ground will be
reduced from that of the perfect ground plane case".

Antenna Theory and Design by Stutzman and Thiele pages 66 & 67: "The
principles of image theory are illustrated in this section with several
forms of the monopole antenna. ... Figure 2-12(c) Practical monopole
antenna with radial wires to simulate a ground plane".

Antennas for all applications third edition by J.D. Kraus page 719: "In Fig
21-9d the solid-sheet ground plane is replaced by 4 radial conductors. Fig
21-9(d) stub antenna with 4 radial conductors to simulate a ground plane".

Antenna Engineering Handbook by R.C. Johnson page 110: "The geometrical
shape of a sleeve antenna, or a sleeve monopole, is sketched in Fig. 4-22a.
If the image of the structure is included, then we have a sleeve dipole as
shown in Fig. 4-22b". Figure 4-22a shows a coax cable with the centre wire
going upwards forming a vertical element, and the braid being connected to a
ground plane. Fig 4-22b appears to show a dipole being formed from a
monopole and its image antenna.

Foundations of Antenna Theory and Techniqes by Professor Vincent Fusco pages
190 and 191. Claims that image theory i.e. image cancellation applies to the
horizontal section of an inverted L antenna. The vertical part of inverted L
antenna is a short monopole i.e. less than a quarterwave long.

However references against this are below.
Antenna Engineering Handbook by R.C. Johnson page 118: "When the ground
plane is of finite size, the image theorem does not apply."

Professor Douglas Miron in his book Small Antenna Design says that the
vertical element is driven against some horizontal elements. The horizontal
elements have canceling fields. He says that the radials are an artificial
ground called a counterpoise that also radiates.

Various books also say about using image theory to analyse corner reflector
antennas.

RF experts appear to disagree with each other over the vertical monopole
with quarterwave radials - Roy Lewallen and Professor Douglas Miron versus
Professor Constantine Balanis and Professor Vincent Fusco.











Hi David,
What does Aristotle have to say on this subject?
Quoting from authorities may have been good enough for the ancients,
but it doesn't have much value here. You have to descend one
level of abstraction down, and use what you should know about
electromagnetic theory in order to understand what's going on
here. If you did, I don't think you'd see any serious
disagreement between the people you've quoted.
73,
Tom Donaly, KA6RUH
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Old January 9th 07, 03:50 AM posted to rec.radio.amateur.antenna
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Default Followon to image theory

The responses from the professors frankly baffle me. If that's what they
said, and if they meant what you think they mean, then yes, I disagree
with the professors. Folks will have to decide whether to believe them,
or me, or learn more about antenna operation so they can come to their
own informed conclusions.

I won't comment on the Navy training manual, recalling some of the
simplifications made in the equivalent Air Force documents in an effort
to make electronics understandable by the target audience.

Roy Lewallen, W7EL

David wrote:
Various books claim that a ground plane reflects the radio wave emitted by
the vertical, and then claim that a ground plane is formed or simulated by
four elevated radials.
I emailed two Professors of antenna theory about this.

Reply from Professor Constantine Balanis:
"The radials should act more as a ground plane. Four of them are usually the
minimum. The more of them, the better the ground plane. The objective of the
ground plane is to reflect the energy from the main element; the vertical
wire".

Reply from Professor Vincent Fusco:
"My view would be that the radials form an image plane, the radials
themselves do not radiate".
. . .

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