Lil'Yeshua, I think that the Sirio CST image of the New Vector 4K may be accurate, but I don't believe the interpretation that Donald and other's suggest (common mode currents on the outside of the cone) is correct either.
Such thinking is convenient for their idea, but IMO it does not fit the fact that there are only two out of phase currents flowing in the radials and the base of the monopole inside of the cone.
I do not believe the cone is coaxial (forming a tapered transmission line as suggested) and I don't believe the cone produces Common Mode Currents on the outside of the radials. As soon as the physical construction of the coax center conductor and the shield is altered in any way...these two wires will begin to radiate, and the longer the wires are the more radiation will occur. This cone is not coaxial. CMC's may be present on the feed line attached below this antenna, but the taper of the cone does not simulate coax above the feed point. Just do an Internet search for coaxial pig tails and you will see what happens if the proper construction ratio for coax is altered.
My Eznec model for my Sigma 4 shows only two out of phase currents flowing in the elements in the area of the cone, and these two currents are very close to having identical magnitudes. When two elements are close together and either in series or parallel and showing an out of phase current condition we will see far field cancellation. This is what we see between the radial elements and the center monopole of the S4.
We also see this cancellation in 5/8 wave ground plane antennas with horizontal radials. We see this cancellation in the S4 style radials on the S4. The only far field radiation will be the small difference that remains between these out of phase elements, and the benefit can be either destructive or constructive...depending on the phase with the strongest total magnitude of current. So, if the 1st segment in each radial shows (-) .33 amps per element for a combined total of (-) .99, and the 1st segment of the monopole shows (+) 1.05 amps...then the results will be (+) .06 amps difference. If the top 1/2 wave element is (-) phase then this (+) .06 amps will be destructive and thus substracted from the max current in the radiator above. Either way the difference is not much.
I see very little far field radiation from the cone on my Sigma 4 model. Depending on how I place the source (feed point) on the radiator, this difference can result in either destructive or constructive addition to the top 1/2 wave element. Either way this result will still be very small.
If you model this antenna with NEC type software you must add a radial hub at the base of the radiator, the segment count for both radials and monopole must be similar in size and count, and you cannot use the taper scheduled noted in the Manual for the elements...you must average the element diameters as close as possible for CB band if you are using the dimensions in the Manual.
If you do this correctly, your model should show a complex impedance that shows resonance with a very low reactance at 27.205 mhz...the middle of the CB band.
Below is my S4 model with the pattern expanded to better show the currents on the elements. You will see the phase difference in the base section at the bottom of the monopole vs. the top 1/2 wave radiator. The currents on the radials are in phase with the top 1/2 wave radiator. The current in the 1st segment of the monopole is a fraction greater, as noted above compared to the sum of the three radials.
Also note that the magnitude of currents note in red on the radials are greater at the base than at the top...and this is the way the current distribution for a 1/4 wave element will look. If these currents on the radials were CMC emanating from the top of the radial elements...these current patterns would be the exact opposite of what we see here.
