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

Bob Camp kb8tq at n1k.org
Sat May 2 13:25:16 EDT 2015


Hi

Obviously this becomes a “that depends” sort of question. For timing, you probably can 
do a fine job with an antenna that nukes everything below 20 degrees to the horizon. That
*assumes* that you have a good enough view that it does not pull to many sat’s out of your population 
*and* that you already know your location. 

Phase / delay stability over temperature would be an interesting thing to look at. Probably not a big deal on 
a simple antenna. It might be an issue as the antenna interacts with the preamp and filter.

Bob

> On May 2, 2015, at 12:36 PM, Magnus Danielson <magnus at rubidium.dyndns.org> wrote:
> 
> Attila,
> 
> 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.
> 
>> But I had to discover that I actually do not know what to optimze for.
>> There are many paramters I can think of (RHCP/LHCP, symmetry of
>> gain, feedpoint impedance vs frequency, stability of phase centre,....)
>> which all seem to be to some extend important, but which ones do actually
>> matter for the timing reference performance?
>> 
>> 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
> 
> Do read up on the Novatel pinwheels, as they illustrate the various concerns and how they do that in a new fashion.
> 
> Cheers,
> Magnus
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