Circular polarization transmission/reception
Circular polarization transmission/reception
(OP)
I have really been struggling with this one: I have read that in a data link for instance, where there is a transmit antenna at one end of the link and a receive antenna at the other end, if CP is used, you want to employ antennae of the same polarization sense. I came up with a simple conceptual model of a CP antenna - two pyramidal horns oriented at 90 degrees - one transmitting H polarization and the other V polarization. The power is divided between the apertures and a 90 deg phase shifter is placed in the H arm of the Tx antenna. The construction is the same for the RX antenna. So, with same sense antennas facing one another in the link, the H polarizaton will experience two 90 degree lags (for a total of 180), and the V polarization will experience zero lag relative to H, so the fields will cancel upon combining at the Rx. Correct? This is not what my text says; however, they offer no mathematical explanation. There has to be another 180 deg phase shift - where does it come from? John





RE: Circular polarization transmission/reception
TTFN
RE: Circular polarization transmission/reception
Suppose your transmit horizontal antenna connector is in LA and it points northward. Your identical receiving antenna in New York pointing back at LA will have the horizontal connector pointing south. There's your other 180 shift north to south.
kchiggins
www.toyon.com
RE: Circular polarization transmission/reception
Thanks,
John
RE: Circular polarization transmission/reception
And if your antennas are circularly polarized, say a basic spiral antenna, for every physical degree it's rotated, your analyzer will show a degree of phase change. That's true is a spiral antenna transmits to a linear antenna on the other end too.
That's a phase shifter technique used by some as a phase adjuster.
kchiggins
www.toyon.com
RE: Circular polarization transmission/reception
You can make CP using two linear antennas arranged at the obvious 90-degree orientation (for example: cross dipoles), and with a 90-degree electrical phase shift in the feed harness. Or alternatively, with one dipole one-quarter lambda further along the boom.
So, provided that you add the required phase shift, then you can make CP from the sum of two linear. And vice versa backwards the other way too of course.
RE: Circular polarization transmission/reception