Yuri Blanarovich wrote:

Likewise,
a purely circularly polarized field can be split into non-zero vertical
and horizontal linear components.

Roy Lewallen, W7EL


Sooo,
we can say that "slanted" 45 deg (circular) polarization as produced with full
wave square shaped quad loop fed in a corner has vertical and horizontal
components that are (typically) 3 dB down from the maximum in 45 deg plane?

You're confusing 45 degree linear polarization with circular
polarization. Even though both have equal horizontal and vertical
components, they're not the same. The difference is that in a linearly
polarized wave, Eh and Ev are in phase. In a circularly polarized wave,
they're in phase quadrature (90 degrees out of phase with each other).
That makes a large difference. Other relative phase angles result in
elliptical polarization with differing axial ratios. In a purely
linearly polarized wave, the amplitude of the field goes from zero to
maximum, back to zero and maximum again, and back to zero each cycle,
and its physical direction of polarization stays constant. In a
circularly polarized wave, the magnitude of the field stays constant,
but its physical direction of polarization rotates through a full circle
each cycle.

According to modeling software, which shows vertical and horizontal components
of slanted polarization, the radiation pattern is a composite of both, with
antenna responding to either V or H polarized waves (with 3 dB down from
slanted) and according to pattern "belonging" to each (V or H) polarization. Is
anything wrong with this statement?

No.

Can we then say that "slanted" polarization antenna has practically "dual" (V
and H) polarization properties with 3 dB down from slanted orientation?

Yes.

Advantage being fuller radiation pattern (minimized nulls) and polarization
"diversity" at a cost of 3 dB from the "ideal" slanted orientation.

The "fuller" radiation pattern doesn't necessarily follow. And it still
suffers the disadvantage that a linearly polarized antenna whose
polarization is slanted the opposite way (at right angles to the wave
polarization slant) will encounter much more than 3 dB attenuation.
That's why circular, rather than slanted linear, polarization is often
used for FM broadcasting.

One "Guru" on his web page claims that there is no such thing as dual
polarization.

Please re-read what I said in my original posting. We're describing a
single wave by mathematically dividing the field into two orthogonal
components, which we can call "polarizations". We can choose horizontal
and vertical linear, left and right circular, or an infinite number of
other combinations, including right-slant, left-slant. A wave has only
one E field; our description of polarizations is one of convenience. If
I choose left-slant and right-slant, I can declare with complete
accuracy that your wave has a single polarization component. If I choose
instead vertical and horizontal, I find that it has two equal
components. If I choose some other combination, I find it has two
unequal components. All are equally valid descriptions of the single field.

The "problem" seems to be in semantics. I see nothing wrong calling it "dual"
polarization, because it produces combination patterns "belonging" to either V
or H polarized antennas, (with 3 dB down from ideal slanted) and fuller pattern
than either of V or H alone.

Suit yourself. Arguing about it would surely be good for at least a
couple of hundred postings, providing an extended diversion for the
entertainment challenged.

It ain't so, am I wrong?

No, you're right. It's dual polarization. And you're also wrong, since
it's also single polarization (left-slant or right-slant linear).

People with a deep interest in this topic might benefit from the new
EZNEC+ program type, which can display the field strength from any
antenna in terms of left and right circular as well as vertical and
horizontal linear components.

Roy Lewallen, W7EL