Art wrote:
"It is not physical size that is important with respect to a dish it is
the wavelength between two objects that counts. A simple helix antenna
can use a reflector in place of a ground plane not used as an optical
ray reflector."

Yes, but, size matters even when you are told it doesn`t. A dish usually
makes the path length equal between its frontal plane and focal point
for all rays by the parabolic curvature of its reflector. Everything
stays in phase by virtue of traveling the same distance through the same
medium. The bigger the dish, the higher the gain.

On the helix antenna invented by Kraus, Terman writes on page 909 of his
1955 opus:
"The directive gain is appreciable, a six-turn helix having a diameter
of 0.30 lambda sith a spacing of 0.30 lambda between turns developing a
gain of 45 when provided with a reflecting screen at the input and that
is normal to the helix axis. A helical antenna is relatively broadband
in its characteristics."

Best regards, Richard Harrison, KB5WZI