Having worked with the Sigma design in the FM broadcast field for many years, I've had several engineers familiar with NEC claim the antenna modeled in the program performed terribly. With a maximum gain occurring at 45 degrees above the horizon. Knowing the information NEC was producing was totally inaccurate, I had little interest in the program.
Henry HPSD has completely changed my mind about EZNEC+. Apparently the new versions of the program are much better at modeling the antenna. Henry HPSD has modeled the Sigma in the program and gave me the file he made. The results looked so impressive I immediately purchased the new version of the program and scaled his model to fit my FM broadcast version. The sidelobe gain was within 0.1db of what was actually measured in the field!
The program also produced a wealth of other important information like a radiation angle of 8 degrees with a beamwidth of 22.9 degrees. Not to mention a beautifully detailed radiation pattern. No 5/8 wave is ever going to produce these results. Typically they have a radiation angle of about 16 degrees.
I also think the longer radials in close proximity to the radiator make them look shorter then they are. However, the longer radials still seem to drop the resonant frequency to some degree. This is easily compensated by adjusting the gamma tap point or radiator length. This could be one reason the new Vector is shorter then 31 feet.
While Sirio doesn't claim more gain, I was taught that the only way to increase gain in an omni directional system is to lower the angle of radiation. By lowering the angle of radiation, you simultaneously compress the beamwidth and produce more usable gain on the horizon. Am I not understanding this correctly?
While the hoop would be 9 feet on CB if you flared the radials out at 30 degrees, it's interesting to note the antenna does not need a hoop to perform. With the hoop removed and the radials lengthened to compensate, the antenna has nearly the same gain with reduced bandwidth. The most notable change was that the gain was not uniform in all 360 degrees. It produced peaks in the directions where the radials were, and nulls where the radials were not.
