Vertical radiation from horizontal dipole?
 

Dear friends:

Could you give me me a link to some reference material (in the net)
about vertical polarized radiation of horizontal dipoles near ground?
(not feed line radiation)..
Thank yoy very much in advance.

Miguel Ghezzi (LU 6ETJ)

Vertical radiation from horizontal dipole?
 

I don't have any link handy, but it's easy to explain.

Ground isn't necessary. Consider a horizontal dipole in free space.
Position yourself directly in line with the antenna, some distance away,
so all you see of the antenna is a dot. Now, move directly upward or
downward. The antenna now looks like a vertical line(*). The radiation
from the antenna at the point where you are is purely vertically
polarized, for the same reason it's purely horizontally polarized when
you're directly broadside to the antenna.

The only directions in which the dipole will radiate a purely
horizontally polarized signal are in the horizontal plane of the
antenna, or exactly at right angles (broadside) to the antenna. In the
vertical plane containing the antenna, it's purely vertically polarized.
In all other directions, it's a combination of the two. (In other words,
the polarization angle of the total field is neither vertical nor
horizontal.)

Here's an illustration you can do with the demo version of EZNEC. Open
the Dipole1.ez example file, which is a dipole in free space. In the
main window, click the Desc Options line. In the Desc Options dialog
box, select the Plot and Fields tabs if not already active, and select
"Vert, Horiz" (not "Vert, Horiz, Total") in the Fields To Plot frame.
Then click Ok to close the box. (Note: The "Vert, Horiz" option, without
the "Total", isn't available in EZNEC v. 3.0, including EZNEC-ARRL.)

The example file is set up to plot the pattern in the horizontal plane
of the antenna. If you click FF Plot, you'll see only a horizontally
polarized field. That's because the field is purely horizontally
polarized in the horizontal plane of the antenna, as I mentioned
earlier. The ends of the antenna are up and down on the plot, and
broadside is to the left and right.

Now in the main window, change the elevation angle to 45 degrees. Do
this by clicking on the Elevation Angle line, entering 45 in the dialog
box, then clicking Ok. This moves the observer above the horizontal
plane of the antenna. The observation point (assumed very far from the
antenna) follows a circle which is equidistant from the antenna and the
horizontal plane containing the antenna. That is, it maintains a
constant distance and an angle of 45 degrees above horizontal from the
antenna. Click FF Plot to see the result. Now you can see that when
you're directly broadside to the antenna (left and right on the plot),
the field is purely horizontally polarized -- the vertical polarization
component is zero. But directly in line with the ends of the antenna,
the polarization is purely vertical. The top and bottom directions of
the plot correspond to the position you were in when you saw the antenna
as a vertical line.

Vertically and horizontally polarized components reflect differently
from the ground. So in directions where both are present, one can be
reinforced while the other is attenuated, resulting in a different mix
after reflection. (But reflection won't change a horizontally polarized
component to vertically polarized or vice-versa.) For example, a
vertically polarized field reinforces when reflecting from a perfect
ground at a low angle, while a horizontally polarized signal cancels.
This ends up enhancing the vertically polarized component at low angles
when both are present. (Remember, though, this is perfect ground -- real
ground, except salt water, behaves quite differently.)

Finally, let me emphasize that there's really only one E field from the
antenna, with one polarization angle. Separating it into vertically and
horizontally polarized components is simply a convenience used for
calculations and as an aid in understanding, much like separating two
currents into common and differential (even and odd) mode components.
The principle of superposition allows us to conceptually split the field
into components, analyze each separately, then recombine the results,
getting the same answer we'd get if we had done the analysis on the
total field.

(*) More precisely, the projection of the antenna on a vertical plane
passing through your position is a vertical line. Visually, you can't
tell if the antenna is a short vertical wire or a longer horizontal one
you're seeing end-on. The nature of the radiation in your direction is
also the same for the two situations.

Roy Lewallen, W7EL

lu6etj wrote:
Dear friends:

Could you give me me a link to some reference material (in the net)
about vertical polarized radiation of horizontal dipoles near ground?
(not feed line radiation)..
Thank yoy very much in advance.

Miguel Ghezzi (LU 6ETJ)

Vertical radiation from horizontal dipole?
 

'One attaboy', Roy... The ARRL ought to include that explanation into
the Antenna Handbook..

cheers ... denny / k8do

Vertical radiation from horizontal dipole?
 

Roy Lewallen wrote:

I don't have any link handy, but it's easy to explain.

Ground isn't necessary. Consider a horizontal dipole in free space.
Position yourself directly in line with the antenna, some distance away,
so all you see of the antenna is a dot. Now, move directly upward or
downward. The antenna now looks like a vertical line(*). The radiation
from the antenna at the point where you are is purely vertically
polarized, for the same reason it's purely horizontally polarized when
you're directly broadside to the antenna.

The only directions in which the dipole will radiate a purely
horizontally polarized signal are in the horizontal plane of the
antenna, or exactly at right angles (broadside) to the antenna. In the
vertical plane containing the antenna, it's purely vertically polarized.
In all other directions, it's a combination of the two. (In other words,
the polarization angle of the total field is neither vertical nor
horizontal.)

Here's an illustration you can do with the demo version of EZNEC. Open
the Dipole1.ez example file, which is a dipole in free space. In the
main window, click the Desc Options line. In the Desc Options dialog
box, select the Plot and Fields tabs if not already active, and select
"Vert, Horiz" (not "Vert, Horiz, Total") in the Fields To Plot frame.
Then click Ok to close the box. (Note: The "Vert, Horiz" option, without
the "Total", isn't available in EZNEC v. 3.0, including EZNEC-ARRL.)

The example file is set up to plot the pattern in the horizontal plane
of the antenna. If you click FF Plot, you'll see only a horizontally
polarized field. That's because the field is purely horizontally
polarized in the horizontal plane of the antenna, as I mentioned
earlier. The ends of the antenna are up and down on the plot, and
broadside is to the left and right.

Now in the main window, change the elevation angle to 45 degrees. Do
this by clicking on the Elevation Angle line, entering 45 in the dialog
box, then clicking Ok. This moves the observer above the horizontal
plane of the antenna. The observation point (assumed very far from the
antenna) follows a circle which is equidistant from the antenna and the
horizontal plane containing the antenna. That is, it maintains a
constant distance and an angle of 45 degrees above horizontal from the
antenna. Click FF Plot to see the result. Now you can see that when
you're directly broadside to the antenna (left and right on the plot),
the field is purely horizontally polarized -- the vertical polarization
component is zero. But directly in line with the ends of the antenna,
the polarization is purely vertical. The top and bottom directions of
the plot correspond to the position you were in when you saw the antenna
as a vertical line.

Vertically and horizontally polarized components reflect differently
from the ground. So in directions where both are present, one can be
reinforced while the other is attenuated, resulting in a different mix
after reflection. (But reflection won't change a horizontally polarized
component to vertically polarized or vice-versa.) For example, a
vertically polarized field reinforces when reflecting from a perfect
ground at a low angle, while a horizontally polarized signal cancels.
This ends up enhancing the vertically polarized component at low angles
when both are present. (Remember, though, this is perfect ground -- real
ground, except salt water, behaves quite differently.)

Finally, let me emphasize that there's really only one E field from the
antenna, with one polarization angle. Separating it into vertically and
horizontally polarized components is simply a convenience used for
calculations and as an aid in understanding, much like separating two
currents into common and differential (even and odd) mode components.
The principle of superposition allows us to conceptually split the field
into components, analyze each separately, then recombine the results,
getting the same answer we'd get if we had done the analysis on the
total field.

Are there multipath solutions using circular polarization
between double side band supressed carrier components?


(*) More precisely, the projection of the antenna on a vertical plane
passing through your position is a vertical line. Visually, you can't
tell if the antenna is a short vertical wire or a longer horizontal one
you're seeing end-on. The nature of the radiation in your direction is
also the same for the two situations.

Roy Lewallen, W7EL

lu6etj wrote:
Dear friends:

Could you give me me a link to some reference material (in the net)
about vertical polarized radiation of horizontal dipoles near ground?
(not feed line radiation)..
Thank yoy very much in advance.

Miguel Ghezzi (LU 6ETJ)

Vertical radiation from horizontal dipole?
 

Green Egghead wrote:
. . .

Are there multipath solutions using circular polarization
between double side band supressed carrier components?

Sorry, I don't understand the question. What do you mean by solutions
between components? Solutions to what? Or is the question about
polarization between components? If so, what does that mean?

The original question and my answer involved only linearly polarized
fields, not circular or elliptical.

Roy Lewallen, W7EL

Vertical radiation from horizontal dipole?
 

Think what he may mean is: if you use a Circular
polarization , it will receive both horizontal,
and vertical polarization signals, equally well
tho at a decrease of 3 dB in signal , vs. horizontal
to horizontal, or vertical to vertical
polarization. A good way to observe this
optically, for LINEAR polarizations, would
be to find an old pair of sunglasses, useing
polarized lenses. break them in two, and then look
throuh BOTH lens's . As you rotate one, keeping
the other stationary, note the loss of light thru
them. At 90 degrees, it should be almost black!
but at 45, degrees, the degree of darkness (this
is for the stationary lens) will be about the same
if the rotated lense is moved either + or - 45
degrees (the equivalent of circular polarization
in an optic field. Don't know if this explaination
helps, but migh give it a try-- Jim NN7K
Green Egghead wrote:
Roy Lewallen wrote:
I don't have any link handy, but it's easy to explain.

Ground isn't necessary. Consider a horizontal dipole in free space.
Position yourself directly in line with the antenna, some distance away,
so all you see of the antenna is a dot. Now, move directly upward or
downward. The antenna now looks like a vertical line(*). The radiation
from the antenna at the point where you are is purely vertically
polarized, for the same reason it's purely horizontally polarized when
you're directly broadside to the antenna.

The only directions in which the dipole will radiate a purely
horizontally polarized signal are in the horizontal plane of the
antenna, or exactly at right angles (broadside) to the antenna. In the
vertical plane containing the antenna, it's purely vertically polarized.
In all other directions, it's a combination of the two. (In other words,
the polarization angle of the total field is neither vertical nor
horizontal.)

Here's an illustration you can do with the demo version of EZNEC. Open
the Dipole1.ez example file, which is a dipole in free space. In the
main window, click the Desc Options line. In the Desc Options dialog
box, select the Plot and Fields tabs if not already active, and select
"Vert, Horiz" (not "Vert, Horiz, Total") in the Fields To Plot frame.
Then click Ok to close the box. (Note: The "Vert, Horiz" option, without
the "Total", isn't available in EZNEC v. 3.0, including EZNEC-ARRL.)

The example file is set up to plot the pattern in the horizontal plane
of the antenna. If you click FF Plot, you'll see only a horizontally
polarized field. That's because the field is purely horizontally
polarized in the horizontal plane of the antenna, as I mentioned
earlier. The ends of the antenna are up and down on the plot, and
broadside is to the left and right.

Now in the main window, change the elevation angle to 45 degrees. Do
this by clicking on the Elevation Angle line, entering 45 in the dialog
box, then clicking Ok. This moves the observer above the horizontal
plane of the antenna. The observation point (assumed very far from the
antenna) follows a circle which is equidistant from the antenna and the
horizontal plane containing the antenna. That is, it maintains a
constant distance and an angle of 45 degrees above horizontal from the
antenna. Click FF Plot to see the result. Now you can see that when
you're directly broadside to the antenna (left and right on the plot),
the field is purely horizontally polarized -- the vertical polarization
component is zero. But directly in line with the ends of the antenna,
the polarization is purely vertical. The top and bottom directions of
the plot correspond to the position you were in when you saw the antenna
as a vertical line.

Vertically and horizontally polarized components reflect differently
from the ground. So in directions where both are present, one can be
reinforced while the other is attenuated, resulting in a different mix
after reflection. (But reflection won't change a horizontally polarized
component to vertically polarized or vice-versa.) For example, a
vertically polarized field reinforces when reflecting from a perfect
ground at a low angle, while a horizontally polarized signal cancels.
This ends up enhancing the vertically polarized component at low angles
when both are present. (Remember, though, this is perfect ground -- real
ground, except salt water, behaves quite differently.)

Finally, let me emphasize that there's really only one E field from the
antenna, with one polarization angle. Separating it into vertically and
horizontally polarized components is simply a convenience used for
calculations and as an aid in understanding, much like separating two
currents into common and differential (even and odd) mode components.
The principle of superposition allows us to conceptually split the field
into components, analyze each separately, then recombine the results,
getting the same answer we'd get if we had done the analysis on the
total field.

Are there multipath solutions using circular polarization
between double side band supressed carrier components?

(*) More precisely, the projection of the antenna on a vertical plane
passing through your position is a vertical line. Visually, you can't
tell if the antenna is a short vertical wire or a longer horizontal one
you're seeing end-on. The nature of the radiation in your direction is
also the same for the two situations.

Roy Lewallen, W7EL

lu6etj wrote:
Dear friends:

Could you give me me a link to some reference material (in the net)
about vertical polarized radiation of horizontal dipoles near ground?
(not feed line radiation)..
Thank yoy very much in advance.

Miguel Ghezzi (LU 6ETJ)

Vertical radiation from horizontal dipole?
 

Jim - NN7K wrote:
Think what he may mean is: if you use a Circular polarization , it will
receive both horizontal,
and vertical polarization signals, equally well
tho at a decrease of 3 dB in signal , vs. horizontal
to horizontal, or vertical to vertical
polarization. A good way to observe this
optically, for LINEAR polarizations, would
be to find an old pair of sunglasses, useing
polarized lenses. break them in two, and then look
throuh BOTH lens's . As you rotate one, keeping
the other stationary, note the loss of light thru
them. At 90 degrees, it should be almost black!
but at 45, degrees, the degree of darkness (this
is for the stationary lens) will be about the same
if the rotated lense is moved either + or - 45
degrees (the equivalent of circular polarization
in an optic field. Don't know if this explaination
helps, but migh give it a try-- Jim NN7K

Unfortunately, it's not demonstrating circular polarization at all.

Circular polarization isn't the equivalent of 45 degree tilted linear
polarization. The polarization of a circularly polarized wave (RF,
light, or any other electromagnetic wave) rotates, one revolution per
cycle. So over each period, the polarization rotates from vertical,
through intermediate angles to horizontal, back to vertical but oriented
the other direction, to reverse-oriented horizontal, back to vertical
again. A 1 MHz field does this a million times per second.

If you view circularly polarized light through polarized sunglasses, the
intensity will be the same regardless of how you rotate the glasses. If
you pass circularly polarized light through one polarized lens, the
light is linearly polarized on the other side. So rotating the second
lens behind it illustrates only cross polarization of linearly polarized
waves.

If you have a purely linearly polarized field, say, horizontal, and
rotate a dipole in a vertical plane in that field (with the plane
oriented so the field is broadside to the dipole), the signal received
by the dipole will be maximum when the dipole is horizontal, zero when
it's vertical ("cross polarization"), and intermediate values in
between. This is the equivalent of the polarized sunglass experiment.
But if the impinging field is circularly polarized, the received signal
will be the same for any of the dipole orientations. This is because the
field is always aligned with the dipole for two instants every cycle
(when the antenna response will be maximum), cross-polarized for two
instants every cycle (when the antenna response is zero), and at some
intermediate relative polarization for the rest of the cycle (when the
antenna response will be greater than zero but less than the maximum).
And the proportion of each is the same regardless of which position the
dipole is rotated to. The 3 dB attenuation relative to a linearly
polarized, optimally oriented field is due to the fact that the
circularly polarized wave is cross-polarized to various degrees during
the cycle and is optimally polarized only for those two instants each
cycle. A dual situation exists with a circularly polarized antenna and
linearly polarized field: a linearly polarized wave of any orientation
is received equally with a right or left handed circularly polarized
antenna. Any plane wave can be divided into either vertical and
horizontal (or any two orthogonal) linear components, or into right and
left handed circular components. Any linearly polarized wave has equal
magnitude right and left handed circular components. Any circularly
polarized wave has equal magnitude horizontal and vertical linear
components. Hence the antenna responses discussed above.

Like a circularly polarized wave, a 45 degree linearly polarized wave
also has equal magnitude horizontal and vertical components. But this
doesn't make it the same as a circularly polarized wave. The horizontal
and vertical components of a 45 degree linearly polarized wave are in
time phase or 180 degrees out of phase; those of a circularly polarized
wave are 90 degrees relative to each other. This essential difference
causes the orientation of the linearly polarized field to stay fixed but
the orientation of the circularly polarized field to rotate. Put two
crossed dipoles close to each other and feed them in phase or 180
degrees out of phase, and you'll get a 45 degree linearly polarized
field broadside to the antenna. Feed them in quadrature (90 degree
relative phasing) and you'll get a circularly polarized field broadside
to the antenna.

Linear and circular polarization are limiting special cases of the more
general elliptical polarization. The polarization of an elliptically
polarized field rotates each cycle, but the amplitude can also vary
during the cycle. The ratio of the minimum amplitude to the maximum (or
vice-versa, depending on the reference) is called the axial ratio.
Circular polarization is the special case of elliptical polarization
having an axial ratio of one. Linear polarization is the special case
where the axial ratio is zero (or infinite, depending on the definition
used for axial ratio). A general elliptically polarized wave can have
different horizontal and vertical linear polarization components, and
different right and left hand circular polarization components.

Roy Lewallen, W7EL

Vertical radiation from horizontal dipole?
 

Roy Lewallen wrote:

Green Egghead wrote:
. . .

Are there multipath solutions using circular polarization
between double side band supressed carrier components?

Sorry, I don't understand the question. What do you mean by solutions
between components? Solutions to what? Or is the question about
polarization between components? If so, what does that mean?

The original question and my answer involved only linearly polarized
fields, not circular or elliptical.

Roy Lewallen, W7EL

By "solution" I mean to the problem of recovering as much
of the transmitted signal strength as possible.
More specifically under typical receiving conditions
where polarization of that transmitted signal
is affected by reflections, atmospheric conditions or
some other cause (what would be other causes?).

I am still confused by the relationship between the absolute
and relative terms, between the spatially and temporally changing
components, and between the analytical versus physical descriptions
of polarization.

Your very helpful follow-up to NN7K both refines and complicates
my understanding.

You wrote there about phasing linearly polarized orthogonal
transmission antennas:

This essential difference causes the orientation of the linearly polarized
field to stay fixed but the orientation of the circularly polarized field
to rotate. Put two crossed dipoles close to each other and feed them
in phase or 180 degrees out of phase, and you'll get a 45 degree linearly polarized
field broadside to the antenna. Feed them in quadrature (90 degree
relative phasing) and you'll get a circularly polarized field broadside
to the antenna.

Please correct me where I am wrong here.
From what you wrote:

One antenna is transmitting a "horizontally" polarized
(electric) field with a time varying electric amplitude A(t):

B_h = A(t)*cos(0) = A(t)
B_v = A(t)*sin(0) = 0

where "horizontal" is represented by an angle of zero degrees
in the transmitter's coordinates, and B_h and B_v are it's
respective horizontal and vertical e-field strengths.

Similarly the other transmitting antenna is vertically polarized:

C_h = A(t)*cos(90) = 0
C_v = A(t)*sin(90) = A(t)

again where "vertical" is represented by an angle of 90 degrees
in the transmitter's coordinates.

Superposing these two fields yields a 45 degree linear field
polarization (45 degrees relative to the transmitter's coordinates)
As far as the transmitter is concerned this polarization will
be the same for every point in free space. This is ignoring the
observer's relative perspective on the transmitter.


To get a circularly polarized field (again, relative to the
transmitter's coordinates irrespective of any receiver)
feeding the two linearly polarized antennas in quadrature
would be equivalent to:

B_h = A(t)*cos(0) = A(t)
B_v = A(t)*sin(0) = 0
and
C_h = A(t+90)*cos(90) = 0
C_v = A(t+90)*sin(90) = A(t+90)

Where A(t+90) represents the signal A(t) shifted
90 degrees relative to the carrier frequency.

Signal A(t) is not equal to A(t+90) at the every point in
free space and so they will interfere. This would create
a spatially and temporally changing carrier amplitude?

Circular polarization is not due to the superposition of
two orthogonal linearly polarized fields at a receiving dipole
where one of the field's linear polarization is rotated
90 degrees with respect to the other. As you pointed out,
that's just a 45 degree linear polarization and it does
not change from one point in free space to the next.

So I don't understand how two same frequency carriers
where one is 90 out of phase with the other creates a
circularly polarized wave since their resultant is not
in the polarization plane but along the direction of
the field's propagation.

Wouldn't the phase between the electric and magnetic
fields have to be different (other than 90 degrees)
to create a circularly polarized wave? If so can
circular polarization be described as changing more
or less than once per cycle?

Any single linearly polarized field can be parametrized
into two circularly polarized fields (represented
as the superposition of two circularly polarized fields).
Therefore, any receiver with a horizontal dipole,
can be described as receiving two circularly polarized waves.
But this would be an analytical description of the receiver,
rather than a physical description of the field that was
actually sent.

What amount of radio signal attenuation is typically
attributed to polarization mismatches?

Thanks for your help, I realize that polarization
can be complicated to describe in full detail.
I do not know much about how it is delt with
in terms of radio reception.

KC2PRE

Vertical radiation from horizontal dipole?
 

Jim - NN7K wrote:

Think what he may mean is: if you use a Circular
polarization , it will receive both horizontal,
and vertical polarization signals, equally well
tho at a decrease of 3 dB in signal , vs. horizontal
to horizontal, or vertical to vertical
polarization. A good way to observe this
optically, for LINEAR polarizations, would
be to find an old pair of sunglasses, useing
polarized lenses. break them in two, and then look
throuh BOTH lens's . As you rotate one, keeping
the other stationary, note the loss of light thru
them. At 90 degrees, it should be almost black!
but at 45, degrees, the degree of darkness (this
is for the stationary lens) will be about the same
if the rotated lense is moved either + or - 45
degrees (the equivalent of circular polarization
in an optic field. Don't know if this explaination
helps, but migh give it a try-- Jim NN7K

I was thinking about something I read a while back
in Paul Nahin's book "Science of Radio" about
synchronized transmitters and receivers,
and about something in Richard Feynman's QED.

Roy Lewallen said several things that for a moment
made me wonder whether quantum entanglement
could be demonstrated in radio waves as it can be
for light. I'll have to re-read Nahin's book.

Karo brand corn syrup has an interesting property.
It will rotate the linear polarization of light passing through it
by different amounts depending on the frequency.
This can easily be seen by placing a small jar of
Karo syrup between to linear polarizers and rotating
them. Different angles between the linear polarizers
will result in a different color being seen in the Karo jar.
Note the color seen also depends on the thickness of
the jar, so if you use a round jar you will see several
different colors but they will still change when you rotate
the polarizers. I was wondering if a radio receiver could be
frequency tuned based on polarization in such a manner.


Green Egghead wrote:
Roy Lewallen wrote:
I don't have any link handy, but it's easy to explain.

Ground isn't necessary. Consider a horizontal dipole in free space.
Position yourself directly in line with the antenna, some distance away,
so all you see of the antenna is a dot. Now, move directly upward or
downward. The antenna now looks like a vertical line(*). The radiation
from the antenna at the point where you are is purely vertically
polarized, for the same reason it's purely horizontally polarized when
you're directly broadside to the antenna.

The only directions in which the dipole will radiate a purely
horizontally polarized signal are in the horizontal plane of the
antenna, or exactly at right angles (broadside) to the antenna. In the
vertical plane containing the antenna, it's purely vertically polarized.
In all other directions, it's a combination of the two. (In other words,
the polarization angle of the total field is neither vertical nor
horizontal.)

Here's an illustration you can do with the demo version of EZNEC. Open
the Dipole1.ez example file, which is a dipole in free space. In the
main window, click the Desc Options line. In the Desc Options dialog
box, select the Plot and Fields tabs if not already active, and select
"Vert, Horiz" (not "Vert, Horiz, Total") in the Fields To Plot frame.
Then click Ok to close the box. (Note: The "Vert, Horiz" option, without
the "Total", isn't available in EZNEC v. 3.0, including EZNEC-ARRL.)

The example file is set up to plot the pattern in the horizontal plane
of the antenna. If you click FF Plot, you'll see only a horizontally
polarized field. That's because the field is purely horizontally
polarized in the horizontal plane of the antenna, as I mentioned
earlier. The ends of the antenna are up and down on the plot, and
broadside is to the left and right.

Now in the main window, change the elevation angle to 45 degrees. Do
this by clicking on the Elevation Angle line, entering 45 in the dialog
box, then clicking Ok. This moves the observer above the horizontal
plane of the antenna. The observation point (assumed very far from the
antenna) follows a circle which is equidistant from the antenna and the
horizontal plane containing the antenna. That is, it maintains a
constant distance and an angle of 45 degrees above horizontal from the
antenna. Click FF Plot to see the result. Now you can see that when
you're directly broadside to the antenna (left and right on the plot),
the field is purely horizontally polarized -- the vertical polarization
component is zero. But directly in line with the ends of the antenna,
the polarization is purely vertical. The top and bottom directions of
the plot correspond to the position you were in when you saw the antenna
as a vertical line.

Vertically and horizontally polarized components reflect differently
from the ground. So in directions where both are present, one can be
reinforced while the other is attenuated, resulting in a different mix
after reflection. (But reflection won't change a horizontally polarized
component to vertically polarized or vice-versa.) For example, a
vertically polarized field reinforces when reflecting from a perfect
ground at a low angle, while a horizontally polarized signal cancels.
This ends up enhancing the vertically polarized component at low angles
when both are present. (Remember, though, this is perfect ground -- real
ground, except salt water, behaves quite differently.)

Finally, let me emphasize that there's really only one E field from the
antenna, with one polarization angle. Separating it into vertically and
horizontally polarized components is simply a convenience used for
calculations and as an aid in understanding, much like separating two
currents into common and differential (even and odd) mode components.
The principle of superposition allows us to conceptually split the field
into components, analyze each separately, then recombine the results,
getting the same answer we'd get if we had done the analysis on the
total field.

Are there multipath solutions using circular polarization
between double side band supressed carrier components?

(*) More precisely, the projection of the antenna on a vertical plane
passing through your position is a vertical line. Visually, you can't
tell if the antenna is a short vertical wire or a longer horizontal one
you're seeing end-on. The nature of the radiation in your direction is
also the same for the two situations.

Roy Lewallen, W7EL

lu6etj wrote:
Dear friends:

Could you give me me a link to some reference material (in the net)
about vertical polarized radiation of horizontal dipoles near ground?
(not feed line radiation)..
Thank yoy very much in advance.

Miguel Ghezzi (LU 6ETJ)

Vertical radiation from horizontal dipole?
 

Green Egghead wrote:
Roy Lewallen wrote:
Green Egghead wrote:
. . .
Are there multipath solutions using circular polarization
between double side band supressed carrier components?
Sorry, I don't understand the question. What do you mean by solutions
between components? Solutions to what? Or is the question about
polarization between components? If so, what does that mean?

The original question and my answer involved only linearly polarized
fields, not circular or elliptical.

Roy Lewallen, W7EL

By "solution" I mean to the problem of recovering as much
of the transmitted signal strength as possible.
More specifically under typical receiving conditions
where polarization of that transmitted signal
is affected by reflections, atmospheric conditions or
some other cause (what would be other causes?).

At HF considerable fading, including selective frequency fading, is
caused by polarization shift. But it's not easy to create a receiving
antenna that's circularly polarized when a ground reflection is involved
(because ground reflection characteristics are functions of both
reflection angle and polarization), and even more difficult to do it in
more than one direction. If you can build the antenna, it should reduce
polarization shift fading. You still have the problem of fading due to
multipath interference.

. . .

Please correct me where I am wrong here.
From what you wrote:

One antenna is transmitting a "horizontally" polarized
(electric) field with a time varying electric amplitude A(t):

B_h = A(t)*cos(0) = A(t)
B_v = A(t)*sin(0) = 0

where "horizontal" is represented by an angle of zero degrees
in the transmitter's coordinates, and B_h and B_v are it's
respective horizontal and vertical e-field strengths.

Similarly the other transmitting antenna is vertically polarized:

C_h = A(t)*cos(90) = 0
C_v = A(t)*sin(90) = A(t)

again where "vertical" is represented by an angle of 90 degrees
in the transmitter's coordinates.

Ok so far.


Superposing these two fields yields a 45 degree linear field
polarization (45 degrees relative to the transmitter's coordinates)
As far as the transmitter is concerned this polarization will
be the same for every point in free space. This is ignoring the
observer's relative perspective on the transmitter.


To get a circularly polarized field (again, relative to the
transmitter's coordinates irrespective of any receiver)
feeding the two linearly polarized antennas in quadrature
would be equivalent to:

B_h = A(t)*cos(0) = A(t)
B_v = A(t)*sin(0) = 0
and
C_h = A(t+90)*cos(90) = 0
C_v = A(t+90)*sin(90) = A(t+90)

Where A(t+90) represents the signal A(t) shifted
90 degrees relative to the carrier frequency.

Signal A(t) is not equal to A(t+90) at the every point in
free space and so they will interfere. This would create
a spatially and temporally changing carrier amplitude?

Yes, that's correct.

Circular polarization is not due to the superposition of
two orthogonal linearly polarized fields at a receiving dipole
where one of the field's linear polarization is rotated
90 degrees with respect to the other. As you pointed out,
that's just a 45 degree linear polarization and it does
not change from one point in free space to the next.

That's right.

So I don't understand how two same frequency carriers
where one is 90 out of phase with the other creates a
circularly polarized wave since their resultant is not
in the polarization plane but along the direction of
the field's propagation.

Here's your error. In free space in the far field, there is no tilt in
the E field in the direction of propagation; the field is what we call a
plane wave. At any instant, the E field is oriented normal to the
direction of travel. If you look at a circularly polarized wave at a
fixed location, you'll see it rotate in the plane normal to the
direction of propagation. If you freeze the wave in time, you'll see
that the field orientation is a rotating vector, again rotating in a
plane normal to the direction of propagation. Think of the path of an
airplane propeller as the plane flies.


Wouldn't the phase between the electric and magnetic
fields have to be different (other than 90 degrees)
to create a circularly polarized wave?

No. Traditionally, polarization refers only to the orientation of the
electric field. Once the phase of the E field is known, both the
magnitude and phase of the H field can be found. The ratio between the
two is called the impedance of the medium, and is dictated solely by the
nature of the medium through which it travels. In free space, the ratio
of E to H is a purely real number (about 377 ohms), so E and H are
always in phase. You can't alter that except in the field close to an
antenna (the near field).

If so can
circular polarization be described as changing more
or less than once per cycle?

No. The field rotates exactly one revolution per cycle, never any more
or less.

Any single linearly polarized field can be parametrized
into two circularly polarized fields (represented
as the superposition of two circularly polarized fields).
Therefore, any receiver with a horizontal dipole,
can be described as receiving two circularly polarized waves.
But this would be an analytical description of the receiver,
rather than a physical description of the field that was
actually sent.

The splitting of a single field into two orthogonal components such as
horizontal and vertical linear or left and right circular is a way of
describing the field itself. It's useful for such purposes as
determining what the response of a particular kind of antenna would be.

What amount of radio signal attenuation is typically
attributed to polarization mismatches?

I commonly see fades of 20 - 30 dB on 40 meters which I can reverse by
switching between horizontal and vertical antennas -- that is, at the
bottom of the fade I can switch to the other antenna and restore the
signal. So it's mainly due to polarization shift. On line of sight
paths, I believe the attenuation can be quite severe. I don't know what
proportion of the frequency selective fading you hear on distant AM
signals is due to polarization shift and how much to multipath interference.

. . .

There should be some good explanations (and undoubtedly also some bad
ones) on the web, and the topic is covered to some extent in most
electromagnetics texts.

Roy Lewallen, W7EL