Peter,
On 04/18/2013 09:15 PM, Peter Monta wrote:
Hi Magnus,
Would not an antenna with a deep zero focus on the earth center help to
reduce earth-noise (ground temperature noise as well as man-made noise)?
It might, although you'd need a large antenna to generate the angular
resolution needed to reject Earth noise while listening to a GPS bird near
the Earth's limb. If you make the tradeoff of using GPS satellites further
from the limb (say at their max separation of ~5 degrees looking from lunar
distance), hoping for less Earth noise, then you're working with a fainter
sidelobe. I'm sure the proper tradeoff is known. The whole problem sounds
much easier if you're merely at GEO.
GEOs have it simpler. Recall that the side-lobe near the earth is
actually quite strong, since the GPS birds antenna makes a first degree
compensation of distance-difference path-loss compensation, so it has
stronger output to the sides than straight down. So, if you look at
signals near the earth, you can see quite good signal.
As for GPS antenna with null, you can mount antennas on a linear boom
and then sum them together with suitable delay, optimize for around 1,4
GHz as it is in the middle between L1 and L2.
I wonder if there's any advantage in combining far-away GPS with X-ray
pulsar navigation (XNAV), which is said to be good to a few kilometers,
though long integration times are needed. For example, the rough system
time from XNAV could enable very long (arbitrarily long?) coherent
integration for very faint GPS signals obtained with a gain antenna pointed
at the Earth.
Multiple sources if feasable to include all the detectors.
Cheers,
Magnus
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