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 - 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-
[...]
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