Form for quadrifilar helix antenna

thingiverse

With cgiacomo's L2/L5 antenna form (https://www.thingiverse.com/thing:4684888), I struggled because I couldn't repair his submitted file, and finally gave up and wrote my own SCAD script. It's just as well because as soon as I did, I thought of things to add. Anyway, the first few I made were with PETG, and I found that the dielectric effects were enough to de-tune it (downward) by about 7%. I suppose that might have been good enough, but my ultimate mission was to create four antennas: one GPS L1 antenna for RHCP, one for LHCP, and then a GPS L2/L5 antenna for RHCP, and one for LHCP, and I was looking for lower losses. So I wrote the attached OpenSCAD script. I also got some PVA filament, and was able to print a remarkably sturdy form which could stand up to the rough treatment you would expect when bending AWG 14 (1.6 mm) solid copper wire and drawing it through the holes in the form. I was able to dissolve the PVA in water at a low boil for about 45 minutes, which brought it to a state similar to al dente pasta, and it took some patience to gradually free it from the antenna. But the result was an antenna with perfect geometry. The script allows you to choose other dimensions, but the two sets of dimensions that I have in this script are for the L1 and L2 antennas. I was able to measure the cross-pol performance and azimuthal pattern of the RH variant of the L1 and L2 antennas, which is shown in the pictures. It's not perfect, but it's definitely much better than I would have been able to achieve by wrestling with wire and being frustrated by not being able to bend a perfect helix section. The script here assumes that 0.141" semi-rigid or hand-formable coax with solid PTFE dielectric is being used, but you can tweak CoaxDia variable as necessary.