[time-nuts] Improving performance of a GPS antenna...?

[Peter Schmelcher]

>I saw a rather expensive GPS antenna made by one of the
>big-name GPS survey equipment mfgrs that was mounted
>on top of a 12 or 15 inch diameter disc about 3/4 inch thick.
>
>Turns out that the disc is made of some sort of RF absorbent
>foam covered by a weather-proofing coating of some sort.
>
>If one were to try to home-brew something like this, where
>would a small piece of the RF absorbent material be obtained
>without having to spend too much $$ for this experiment?

You might have been looking at a Stealth ground plane antenna.
http://facility.unavco.org/science_tech/dev_test/testing/zephyrperformance.pdf

I recall seeing a long time ago a CAD image of a ground plane disc (non 
metallic?) with lots and lots of holes. The hole to material ratio 
increased with radius I guess to match the free space impedance at the disc 
edge and eliminate diffraction.

These guys had a different idea
http://webone.novatel.ca/assets/Documents/Papers/gps_pinwheel_ant.pdf

page 19 and 20 show a gps antenna on a robotic arm getting calibrated
http://www.oregon.gov/ODOT/HWY/GEOMETRONICS/docs/presentations/1-11-12_OGUG-Improvements_NSRS.pdf?ga=t
Then of course you can also correct for the phase center variation of the 
transmitting antenna.
http://www.iapg.bv.tum.de/46790-bD1lbg-~iapg~forschung~gnss~antenna.html