I understand from books I have read, that a ground mounted vertical
antenna needs many radials. IIRC, the point of diminishing returns on
adding radials falls somewhere between 64-128 radials. I imagine the
best radial-based ground I could have for 20 meters would be a solid
copper disk with about 16 feet radius, give or take. However, I
recall in the ARRL Antenna handbook, not the latest version, but one
prior to this one, there is no noticeable difference between a raised
ground plane antenna with 4 elements as opposed to 128. (From here,
or another antenna forum, I heard for the first time that it holds
true for two radials.)
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Instead of an approx 16 ft radius disc ,you might consider an area
covered with chicken wire mesh with the antenna in its centre.If that's
laid on a lawn the grass will quickly grow over it . In a few weeks time
the wire mesh will no longer be visible and the lawnmower can just run
over .
A Butternut (vertical)antenna with a mesh ground plane compared with
none gave an improvement of 1 to 2 S points on 20 ,15 and 10 m.


Frank GM0CSZ / KN6WH