On 5/8/15 11:37 PM, Poul-Henning Kamp wrote:
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In message <fc02a5e8-5396-4474-a307-546e10909...@n1k.org>, Bob Camp writes:
The “put the antenna up and rotate it to see what happens” experiment
has indeed been done. The objective was not correcting the antenna’s
issues, but validating that their model of the antenna’s phase
center was correct. They were trying to see if anechoic chamber
data really gave correct answers in free space.
So this could be a realistic way for us to calibrate the phase-center
of an antenna ?
Yes.. actually, the best way in the long run would be to collect many
hours of GPS satellite data (carrier phase) with the antenna in one
position. Then rotate the antenna to a new position, collect a bunch
more data, repeat, etc.
Then, you post process using the known position of the satellite, which
gives you a direction of arrival relative to the antenna.
You probably don't need so have a real precise position for the antenna:
the apparent motion of the phase center as a function of az/el is
probably fairly slow.
Isn't that how they collected phase center data for all those antennas
on the UNAVCO site:
http://facility.unavco.org/kb/questions/458/UNAVCO+Resources%3A+GNSS+Antennas
one of the reports has this interesting statement:
Antenna rotation tests work well to identify inconsistencies in mean
phase center offsets. By occupying a short baseline (less than 10
meters) and rotating the antenna orientation 180 degrees it is possible
to see changes in the baseline length caused by the antenna phase
center. For antennas of the same type, the rotation tests will highlight
variations of an individual antenna relative to the pool of antennas.
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