[opendtv] Re: MIMO

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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