John Passaneau wrote in
:

....
Hi:
We just had a member that works in the satellite uplink/downlink
business at Penn State University give a talk on the subject. The
satellites use polarization as part of the frequency sharing system in
geostationary satellites. When they buy time on a satellite they are
given a frequency and a polarization to use. As there is a limited
band of frequencies they use polarization to help share frequencies
with some working horizontal and some vertical. The feeds on the
dishes they use for uplinks and downlinks have motorized polarization
feeds and they adjust them to the requested polarization.

Yes John, I talked about that and I incorrectly used the term
"diversity", but it is frequency reuse as I noted using polarisation.

This can be done with circular (LH and RH) polarisation without a need to
rotate the feed unit, which for many installations will mean another
rotary waveguide joint which is to be avoided.

Launching circular polarisation in a feed horn is not difficult, and
developing autotrack error signals is relatively easy. An interesting
feed for amateur applications is the septum feed which gives access to
both circular polarisations from a fairly simple feed unit.

Owen