Re: 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


.

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