At 04:36 PM 3/21/2018, Greg D wrote: p.s. All this said in the thread, I am a still bit confused. I thought circular polarization was like nuts & bolts. You can thread the nut on a bolt with either piece in either direction; the thread on them doesn't change just because you picked it up "backwards."
Beautiful visual, but the electromagnetic waves don't work quite like that.
If the waves went IN to the antenna from the back, and came OUT the front, like your bolt, then your picture would be perfect.
The EM waves come OUT both front and back of the transmit antenna, so its a mirror image situation.
If you visualize the electric vector rotating around in the plane of the antenna, just like the second hand of the clock, and then you visualize the wave coming out either side of the antenna, starting at the tip of the second hand and moving away from the antenna at the speed of light, you will see that on one side you get a helix that screws one way, and on the other side you get a helix that screws the other way.
Three dimensional stuff is always difficult to visualize correctly. Its one of the reasons I never took up flying.
I can see the possibility of a reverse polarization in the side lobes, but out the back of the antenna shouldn't it be the same as the main lobe?
Side lobes, back lobes, all names for lobes other than the main forward lobe of an antenna. In general, when there are multiple lobes from a circularly polarized antenna, some of them will have one polarization, and some the other. They alternate, ie the 1st order lobes will be flipped from the main lobe, 2nd order lobes will be flipped from the 1st order lobes, etc.
The simple clock example I gave is most like a simple crossed dipole, which has only front and back lobe. If you have a more complex antenna, which squishes its main beam smaller, it will typically have more lobes, some of which we call side lobes, and yes, those first order side lobes will have polarity reversed from the main beam.
Or am I nuts (pun intended)?
Perhaps its simply a polarizing discussion.