Well, I used a Yagi optimizer at one point. With that system, the antenna was parameterized. I specified certain fixed values, like overall boom length and no

Well, I used a Yagi optimizer at one point. With that system, the antenna was parameterized. I specified certain fixed values, like overall boom length and nominal element diameter, and total number of elements. The element lengths and spacings were free for optimization. Fitness function was a scoring of front-to-back ratio, front-to-side ratio, and max allowable SWR over a frequency range of interest, with a goal of maximum forward gain. The optimizer tuned the free variables. For different applications the various scoring measurements would be adjusted differently. (Sometimes you care greatly about minimizing back and side lobes, other times not so much, for instance.)