(1) Is there a data file for this antenna that you can share I can load into a modeling/simulation software?
(2) Peak gain seems to be around 710-720 MHz. What would you do to shift that to around 610-630 Mz?
(3) What effect would using copper plates for the three elements and 1/4" copper pipe for feed do?
(4) Are there corrosion concerns around where the M6 bolt assembly meets the plates, are they of different material?
(5) Would it possible to see a picture of antenna of the antenna where the feed assembly between the antenna and the reflector is more clearly visible?
1) I have *.aedt files (Ansys Electronics Desktop, up to version 15.0 it was called Ansys HFSS and file was *.hfss). I can upload all *.aedt for any antenna I've ever posted description.
HFSS supports geometry export to these files:
2) If you look on antenna directivity in terms of its aperture
it has maximum aperture at ~500 MHz and it slowly decreases up to 710-720 MHz
It's more efficient ~500 MHz and absorbs more energy (for given EMI flux).
But when you translate aperture in terms of beam directivity, beam angle should become narrower faster, since it's releated as square of wave-length to aperture.
I don't understand what you want to achieve. At 600 MHz this antenna has aperture efficiency 125%, and 175% at 500 MHz which is very high (top-perfomance for dozen types of antennas I've ever seen). If you want more gain/aperture at lower freq, you need to increase sizes, since 175% is already astonishing efficiency.
If you are satisfied with aperture 125% @ 600 MHz and just want some rejection filters >710 MHz - maybe it's possible with TR-line network filters (or it's LC-network equivalent)
3) no effects, any non-ferromagnetic material (no iron/nickel in skin layer) will perform identically. 4x0.5 @ h=8 mm line has Zo=156 Ohms. 1/4" round wire has Zo=156 Ohm if spaced 18.3 mm from ground
4) no concern, since no currents there and if no salts solution (no sea water) it's not corrosive. Original industrial version has plastic radome. If you have sea around and no radome - treat joints with varnish.
5) this antenna has 2 versions: original industrial version (and it's DIY clones).
Detailed CAD screenshots and photos of this version on 1st post:
What I personally don't like:
1) Wide band 487-818 MHz (SWR<2) for russian market
2) Excessive SWR <487 MHz and ~600 MHz
3) Gain drop @ 513 MHz (TR-line become 0.25 lambda and resonate with patch and distorts radiation pattern)
4) complicated TR-Line
So I optimized and simplified design:
1) 470-700 MHz band, rejection 720+ MHz
2) moved TR-line close to reflector so it never resonates with patch
3) extremely simple TR line - straight strip
The end of TR-line can be connected many ways:
1) soldered on top of pin of F-connector (female), as in industrial design. Coax cable goes to backplate
2) soldered to F-connector "end face to end face", or supporting PCB plate, coax cable goes from the inner side of reflector
3) mount LNA and TR-Line goes to LNA