George, I remembered your comment above while I was writing my response to your later comments about my analyzer and SWR results to 007.
I never did respond, because I had only seen pictures of the SGM, but now I've seen it and done some of my testing results, and I see very similar factors that Sirio presented in their manual albeit the modeling was done in free space.
You mention current maxima. Surprisingly I see two dips in my bandwidth curve using my analyzer and thus the same shows up on my bandwidth curve graph. In your comments above you suggest that a 5/8 wave dipole, current maxima would not be in the center. Where would you imagine the current maxima to be then? If I show you mine will you show me your's? Can you draw us an image like Bob does using EzBob or like below.
View attachment IMG.pdf
When I modeled a vertical 1/2 wave radiator in free space I saw the typical one current maximum in the middle of the radiator, just like we always see. However, when I added the length necessary for the radiator to be 5/8 wavelength, the current distribution on that antenna had a dip in the middle that suggested a current maximum on both sides or two current maximums. Again, this confirms for me what Sirio published in their manual. If you look at their suggested RF pattern from their modeling software you will also see the dip in the center of the pattern with two current maximums to both sides of the center.
All of these image representations are created by man, trying to describe what is likely to be in nature and physics. I can't tell you what is correct or not, but I do try to get my mind around these ideas...using such symbols.
Personally I believe if there is any advantage with the SGM over other 5/8 wave vertical antennas it has more to do with the improved symmetry in design and the effective feed line decoupling idea that is suggested than any other factor. I doubt there is a compromise or optimized idea for most any effort, that by itself will ever defeat a design with superior symmetry.
I've said it before, but not very often. I am amazed to see some of the results I'm seeing while using my new Gain Master. I can't claim my on-air results are 100%, but testing over the years at this location seldom shows me real significant differences...even when the installations are not real close to equal.
I wasn't impressed on first installing my SGM, but that has all changed now that I have it up with some height.