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

[glenlist]

Carsten, around the edges of the patch are all fringing fields, so the 
required coupling to the plane may be quite low, depending on the design.

The compromised ground plane may also be permitting some rear size 
pickup - multipath !

I'll do some EM modelling later to try and put some numbers on the 
requirements. Those numbers to date were for the ideal scenario.

If there are rear side pickup issues, a screen / plane at least a few 
wavelengths (19cm) square would stop the patch seeing the reflections / 
rear sensitivity without being tightly coupled or connected to the patch 
ground.

Maybe that is what you are seeing when you mention that you've 
experienced poor performance without an additional plane. I don't know 
for sure.

I've only built patches that were high performance, no compromises- It's 
likely the mfrs are intentionally throwing away low angle sensitivity 
and axial ratio equality , and rear pickup rejection to get the size 
down as it still suits the majority of users.

What you can try is turn the patch upside down...and  under the patch at 
least 10cm away, use a sea of steel wool (maybe 50x50cm ) to act as an 
effective absorber (so the sky wont reflect back underneath) .

-glen

On 31/05/2022 20:23, 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-
>> [...]