The heart of any antenna is the active element at the feed point. For a dish antenna and circular polarization, a helix makes a good element.
Here are some pictures of how I built my own to go along with the Drake downconverter (blue box visible in some of these pictures).
The reflector is a piece of sheet aluminum, crudely cut into a circle then spun on my drill press to make it pretty.
The helix is #12 copper wire, wound around a 36mm socket.
To reduce feed line losses at 2.4 GHz, the downconverter is connected directly to the feed point.
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