[time-nuts] Re: Realtime comparing PPS of 3 GPS

[Lux, Jim]

On 5/31/22 3:23 AM, Carsten Andrich via time-nuts wrote:
> On 31.05.22 01:10, glen english LIST via time-nuts wrote:
>> Be aware not to confuse the antenna ground plane  (the patch will 
>> always have its own plane because the top metalization must be fed 
>> against a plane or counterpoise -Â  and a ground plane behind the 
>> antenna.
>>
>> I can see the usefulness of the larger ground plane for any purchased 
>> patch antenna to reduce the likelihood of interference underneath (if 
>> the feed coax has a good RF contact with the plane), and if the plane 
>> is coupled well, it may improve the low angle response .
>>
>> The supplementary ground plane doesnt have to have a galvanic 
>> connection if the gap between the underside of the patch is low- IE 
>> use purely a capacitive coupling to tie the patch antenna ground to 
>> the large ground sheet-
>> [...]
>>
>> That means reducing the gap to about 0.05mm  OR increasing the area- 
>> probably means using a bigger patch.
>
> Hi Glen,
>
> thank you for the insight. I was referring to a ground plane behind 
> the antenna.
>
> Gaps below 1~2 mm between a magnetic "puck"-type patch antenna with 
> IP67 housing and an external ground plane seem practically challenging 
> to me. When it comes to stacked patch multi-band antennas like u-blox' 
> ANN-MB [1], the gap between the top patch and the external ground 
> plane is probably significantly higher. Yet, u-blox generally 
> recommends the use of a symmetric ground plane for the RTK 
> applications [1,2]. From my experience, the M8P and F9P RTK fix barely 
> works without a ground plane under the u-blox antennas.
> While it's just an empirically educated guess, I'd assume that what is 
> required for RTK will not hurt for timing.
>
> Could you share your expert opinion on this? My antenna expertise is 
> admittedly limited to reading data sheets and picking the right one 
> for the particular RF measurement requirements.
>
> Thanks and best regards,
> Carsten

I would think that the large grounded sheet below the antenna helps more 
for making the pattern uniform, and, to a certain extent, suppressing 
some multipath coming from "below" the plane of the sheet.  - not as 
good as a choke ring(s), but not bad.

That is, the sheet is not intended to couple to the antenna's ground 
plane, but is there as a predictable surface (and, probably, to provide 
a magnetic material for a puck to stick to).

As such, the distance from the antenna's ground plane is not 
particularly critical.