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

[Carsten Andrich]

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

[1] 
https://content.u-blox.com/sites/default/files/ZED-F9P_IntegrationManual_UBX-18010802.pdf#page=114
[2] 
https://content.u-blox.com/sites/default/files/ZED-F9P-MovingBase_AppNote_(UBX-19009093).pdf#page=8