[opendtv] Re: MIMO
- From: "Albert Manfredi" <bert22306@xxxxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Mon, 30 Apr 2007 20:39:23 -0400
John Shutt wrote:
How is it possible to have a circularly polarized omnidirectional signal?
You can have a dual horizontal and vertical polarized high power UHF
television transmission antenna, which is what passes for "CP" in the
broadcast world, (or if the power ratio is not 1:1 it is called
"elliptical"
as you correctly pointed out,)
I don't understand this, if you are talking about transmitting antennas.
A vertically polarized omni transmitting antenna is possible, no? And ditto
for a horizontally polarized transmitting antenna.
Now transmit the vertical waveform 90 degrees ahead of the horizontal and
you should see clockwise circular polarization. Make v a cosine, h a sine.
Instead if you transmit the horizontal as a -sine and the CP should be
counterclockwise. (Same if you transmit the vertical as a -cosine but leave
the horizontal unchanged.)
It's the vector sum. If you think of transmitting a pure +cosine wave, at 0
degrees the peak is vertical and the sine in the horizontal is 0. At 45
degrees, the vertical is down to +0.707 of peak and the horizontal has gone
up to +0.707, so the sum appears as a vector rotated 45 degrees to the
right. And at 90 degrees, the vertical is 0 and the horizontal is at its
peak. Isn't that a circularly polarized field emitted omnidirectionally?
Bert
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