But since you are looking at the signal from the other side (the back) of the helix, the circular polarisation appears reversed. Reflecting it changes this so that it is in phase.
Think of a clock, built from invisible materials except for the hands. If you stand in front of it, the hands rotate clockwise. Stand behind it and they appear to be turn anticlockwise. Look at the rear that is reflected in a mirror and they moving clockwise again.
Now, imagine that radio wave coming towards you....
So, positioned correctly, a reflector behind a helix will add to it's gain and reduce the beamwidth, won't it?
Sil ZL2CIA
Robert Bruninga wrote:
Helix antennas being circulary polorized have rejection to the opposite rotation generaly caused by reflections provided that both...
Wow, interesting. I just realized then, that the "reflector screen" at the back of a Helix is not adding any gain then. Because it is true, that any reflected energy will be the opposite circularity! Thus it cannot add in phase to the direct wave.
I guess all the ground plane is doing is providing a counterpoise for the feed system. Oh, and possibly a degree of attenuation to ground noise... Both well worth the metal, I guess. Comments?
Bob, WB4APR
Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb