[time-nuts] Important parameters for a GPS/GNSS antenna

[Attila Kinali]

On Sat, 02 May 2015 18:36:30 +0200
Magnus Danielson <magnus at rubidium.dyndns.org> wrote:

> On 04/29/2015 10:43 PM, Attila Kinali wrote:
> > Moin,
> >
> > I recently discovered openEMS[1], which is, very simply put, a fancy
> > antenna simulator. I played a little with it and thought about
> > trying to optimize an GPS patch antenna design for timing use.
> 
> Will take it for a test-drive to see how it align up to NEC2 and variants.

I'm pretty sure that OpenEMS will be more accurate in most cases.
OpenEMS uses a more general approach to solving Maxwells equations
that works for patterned conductors as well. While NEC2 is known
to work well only for wires and cylinders (even tappered antennas
cause large inaccuracies).
 
> > My google skills failed to locate any relevant documents on this topic.
> >
> > Could someone be so kind and give me some pointers, what to search
> > for, documents or the like?
>
> The thing that we care about is:
> 
> 1) LHCP surpression
> 2) Directivity/ surpression of signals below say 5 degrees above horizon
> 3) Phase stability with regard to azimuth/elevation
> 4) Relatively flat gain above 5 degrees

Yes. In the meantime I found [1]. I only skimmed over an electronic
version so far, but the gist of it seems that multipath supression comes
first, before anything else. Ie RHCP/LHCP ratio and supression of everything
below 5°-10°. After that, it's phase center stability.
Other factors do not seem to matter as much (not sure, it could be
that I just didnt read enough of the book)

> Do read up on the Novatel pinwheels, as they illustrate the various 
> concerns and how they do that in a new fashion.

I read most of the papers and the patents I found. While enlightening
on some aspects, they do not tell much about the tradeoffs.
Also I had some facepalm-moments on what is patentable....
But then, the first pinwheel patent is to expire in 4 years, so that
problem solves itself.

			Attila Kinali

[1] "GPS/GNSS Antennas", by Rama Rao, Kunysz, Fante, McDonald,
2012, ISBN: 978-1596931503

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