Going back to software filtering brings us full circle. ;-)
Searching the interwebs, I found this:
http://www.ll.mit.edu/mission/aviation/publications/publication-files/atc-reports/Dinius_1995_ATC-238_WW-15318.pdf
They more or less state the obvious, but do provide some test results.
Now the obvious is you want good cross polarization, i.e. the ability to
reject the wrong polarization. Basically the intended signal is RHP, but
the direct bounce is LHP, so you want the antenna to have good RHP gain
and poor LHP gain, or more accurately, the ratio between the two.
The next source of interference is the bounce from the ground, which
could be multiple hops and thus potentially RHP. That is where a ground
plane or choke ring came in handy.
Page 37 has the conclusions.
I have a similar Trimble patch somewhere (Trimble 16248-50). It has
never seen action (at least by me) since the voltage requirement is
quite odd. I don't have it in front of me, but I think 4.5v. That
particular antenna also has a SAW filter in it. It is a Navy item.
On 4/2/2012 10:15 PM, Hal Murray wrote:
c...@omen.com said:
Presumably a timing antenna would block low elevation signals to reduce
multipath.
Maybe, but there is a software aspect to the filter. You get to select the
elevation angle.
I don't remember seeing any specs about the filtering angles of various
antennas. Has anybody seen something like that?
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