Here are a collection of antenna gain patterns with the antenna power source located at various heights at 500 MHz. The heights are indicated in the name of the images and were located at 3cm, 6cm, 12cm, and 24cm from the base. One thing to note is that the power source becomes longer as a function of height (since it's connected to the ridges, which slope back). 

The 3D gain plots attached show the gain becoming more uniform until we get to the last one, where it seems to reinvert and be much stronger in the upward direction than below. I'll update this post with some polar slices for a more complete comparison between them.

EDIT: 07/17/23

I've made a few adjustments and added plots of them.

• First, I separated the ridges. Previously, the ridges touched at their inner corners. This electrically connected them and may be why we saw very high peaks in the first set of impedance plots. You can see the plots named Separated_Impedance_<x>_cm.png.
  • This appears to have lowered the peaks considerably and also shifted them to lower frequencies. The peaks are still high when the source is placed high.
  • We seem to be developing another peak at higher frequencies, although this also existed in the previous tests for the high sources.
• After this, I added a waveguide and positioned the source between the extensions of the ridges into the waveguide. I've also added a picture that shows the waveguide in the geometry. 
  • The sources here are positioned from 1 cm below the ridges to 8 cm below the ridges. The naming convention is the same as above, except it includes "Waveguide" in the name.
  • The peaks are considerably lower here and seem consistent as we place sources further down. They are all below 500 Ohms, compared to as much as 4000 Ohms in the previous tests.

EDIT: 08/10/23

I've been trying more tweaks to the design to get rid of the peaks we see in the plots below. I'm having trouble actually getting the impedance to match close to the 50 Ohm value we expect from the cable. The best case situations seem to come from when the ridges are still touching, which we don't want. Here are the properties I've been changing:

• Ridge positions (gene in GA)
  • We don't want the ridges to touch, but I can't get them to be very far from each other anyway. The minimum wavelength in our bandwidth would be 20 cm, but that's close to the size of the bottom of the antenna for when we make it large, so the separation is still small.
  • When the ridges do touch is actually when I get the best matching,
• Bottom size (gene in GA)
  • I've been changing the size of the bottom of the antenna. This is something that can change substantially between individuals in the GA, so even if I find a good value for this, the impedance it gives wouldn't be the same for all individuals we see in an evolution.
  • This does seem to move the location of the impedance peak (in frequency) but I can't seem to get it fully out of band.
• Waveguide length
  • I've been changing the length of the waveguide between 3 cm and 10 cm. We said that somewhere in the middle should be the most reasonable (the example antenna we saw looked to have a waveguide of ~5 cm long). It seems like the source position is more important.
• Source position
  • I've been moving the position of the power source inside the waveguide. This seems to move around the peak and can lower its height, but I haven't been able to get peaks lower than ~400 Ohms, except in cases where the ridges are in contact.

I've added a picture of the best impedance I managed to get, but this involved an antenna with a small base and ridges touching. My next step is to just try a grid search by making many antennas automatically and simulating them all to look for any that have a nice impedance in our band.