this is the solution to add a couple of db to the gain of our Helicals.
The antenna in the picture is a 5705 Mhz 16 turrn helical with 19dbi gain...
The truncated reflector adds another 2dbi as opposed to a flat plate reflector.
To build the reflector, the bottom side of the truncated cone has to have a diameter of 0.75 λ , and the top side of the cone has a diameter of 2.5 λ -- depth is 1/2 λ
It can be useful for 5.8 and 2.4 antennas for VERY long range, with trackers.
This antenna in the picture is a record contender...as we know 19.6km has been done with a 12turn helix and flat plate reflector on 5.8ghz.
Will report back as soon as I am ready to fly it.