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 - 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.
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