SIGMA IV Details

[BOOTY MONSTER]

is it possible that since the cone is containing the radiation from the vertical within it and has an opposing current on the outside in phase with the remainder of the vertical that the cone makes the vertical act like it's only the wavelength of the vertical above it ??? for example on a 3/4wl version it sees the vertical length above the cone as a 1/2 wave ..... and on the taller versions the vertical above the cones ring acts like a 5/8 ? the cone does seem to behave in a few ways like coax ..... but i'm just guessing

 

[W5LZ]

Has an off center fed 3/4 wave vertical antenna (fed at 1/4 wave from the bottom) been modeled and the result compared to thi antenna?
- 'Doc

 

[Zman]

I dont even TRY to figure the antenna out i just put it up and talk off of it...

 

[Marconi]

Marconi,
I looked at the pdf. I get lost in all the rows of data, so I probably miss a lot.
What I notice in your post is that you refer to the cancellation of the cone against the vertical radiator, but make no mention of the in phase currents on the outside of the cone we have all discussed before.

If those currents are not revealed by the Eznec model, then it could be true that Eznec fails to model all the activity going on with the Sigma/Vector antennas. The animated model supplied by SW shows the canceling currents inside the cone, but also shows a radiating in phase current on the outside of the cone.

I see why you'd like to know whether there is any further data to go along with the graphical model he has provided, but again, I'm not so sure Sirio gave him more than the graphic we've been looking at.

There seems to be evidence in your model to support the in phase radiation of the cone and the vertical on the V4k. Your model shows an 8° cursor elevation, and no outstanding lobe at 43° as you pointed out. We all know that a 3/4ƛ antenna will have a predominant lobe at a very high degree of angle, so something is bringing the TOA down toward the horizon and reducing the typical high angle TOA of the 3/4ƛ antenna in your model. I think it is owed to the work of the in phase radiation of the outside of the cone at best, or of the ability of the cone to shield and cancel the the negative effect of the lowest 1/4ƛ of this antenna. Then there id=s the question of whether, and why, the antenna shows more gain on the horizon. Might this not be because of the booster effect the in phase radiating of the cone?

This kind of puts me in mind of how NASA used the gravitational force of both the Earth and the Moon to get the spacecraft to travel to the moon and back. Without the calculated use of these gravitational bodies there would have been no way to power the craft that distance. Maybe the lower radiation helps to slingshot the RF toward the horizon . . ? Oh, well, not likely. But it does seem to help pull it downward toward the horizon.

Perhaps more could be learned by modeling other wavelength antennas with an without a cone shaped set of radials, as well as producing a model of the 3/4ƛ antenna with a typical set of radials and a variety of angles upward and look closely at the data Eznec supplies.

Just thinking out loud . . .

To tell you the truth Homer, I did just as you suggested. I started with a standard 3/4 wavelength radiator, and 4 x 107" inch horizontal radials. As anticipated, I got the typical bad looking, bad acting, high angled antenna we might expect.

Then I started raising the radials up, first at about 40* degrees, and went on up in a couple of steps...untill I got close to the slant we see in the Sigma/Vector.

I've posted about this already, and that was just recently when Shockwave suggested that I may have gone up too high with the radials. I showed him a picture of the bottom of my Vector, which I had been working on...and told him that the model dimensions were based on those that Bob posted sometime back.

In fact, it was this experience with this 3/4 wave project that got my attention on the Vector. This is when I decided to try and get it to specs too, just like I did with my Sigma4.

Homer, the point I want to make about the current log is not in all the details. Each line of information pertains to only about 3" of space on this model, and we don't get much out of looking at all the details.

Step back a little and consider the individual wires and where they are on the antenna. For and antenna maker, that should not be difficult to do. This is where I added notes, hoping it would help a little by describing the parts.

Try just considering the sign of the phase for each wire in the antenna. This is what helps us determine cancellation and radiation. The number values are basically meaningless for this discussion. Do you understand any information from the numbers referred to in the visual graphic Shockwave provided? If not, then you get my point here. If you do understand those numbers and they tell you something of value, then you are well beyond all of this understanding, and you need to be describing what you see to me, instead of me to you. I would like to see all of the numbers that support that small range of numbers though.

Back to the point, I'm trying to make regarding what is likely radiating and what is not. When the signs are all - phase, it indicates wires are in phase and radiating. When the signs are all + phase, it means things are in phase and radiating. However, when two wires have different a phase...is when we see cancellation.

This is the only point I was trying to make, and this is where I see evidence that the bottom of the Vector does not appear to radiate effectively. I posted this currents log for no other reason than to provide such info...about the phase of the wires in the Vector.

I think you indicate that you see phasing information in the Sirio graphic. I also sense you are trying to assume that there are two kinds of current on some wires, and that there is a difference between one side of an element vs. the other side. This idea has been proposed I think, but just saying the words doesn't support or prove anything but opinions, and to be sure...that is all I'm doing here too.

There may be the difference you see in this 1000 x the blink of and eye event we imagine with RF, because we are dealing with alternating currents. But man's ideas trying to visualize this is very limited, and I just don't see this image telling the real truth regarding the phase of these currents. The graphic is impressive however, and it does suggest what the author is saying I suppose, but we are trying to apply real time to an event that happens millions of times a second, and that is hard to visualize in real time. I guess my problem is trusting the words I hear from guys that like what they see and suggest they fully understand what is going on, without question. I know that is not happening, even if the text is read and understood. On the other hand the real data goes a long way in explaining what is going on. But folks have to make an effort to try and understand what folks say, or all is for naught. I'm not giving up on anybodies ideas...just because it is a hard subject to understand. Again, this is why I ask Shockwave for his help in explaining what he presents by showing us the current and phase data.

In a very general sort of way, the guys who invented the method of moments algorithms found mathematical ways of stopping and measuring currents, and their determining the results at a specific point in time. Our computers just handle the calculations for us very rapidly. This process produces a lot of data. The guys that designed this simulated feature in the software that Sirio uses is trying to manipulate the data in an interactive way so we can better visualize the events at a speed we can better understand, but information is limited at AC speeds, and we are left with the understanding of others as to what it really means and for sure what it looks like. And then the viewer applies his own twist to what he sees, and therein lies the issue I raise.

I just can't understand the red indicator being on one side of the antenna at the top and on the other side at the bottom, but I'm like you, I see it telling me I'm seeing phasing going on. When I see phasing going on in Eznec, the red current indicators are typically represented as being on the same side, and when out of phase is going on...the opposite is occurring.

This is different from what the Sirio software is suggesting. So, I have to ask, why?

IMO, either one of the software designer's probably could have designed these currents to show up either way, but they didn't. I have proof of what Eznec it showing, now I want to see what CST software current data and phase detail shows us.

Look at this pattern. Can anyone tell me what antenna this looks like is being intimated? Then tell me if this is the way you thought this particular antenna worked?

That said, my Eznec provides the tabular current list that you find so difficult to visualize and we are lucky to have both ideas to consider with Eznec. I'm just asking Shockwave if he can do the same with his software scheme. You could look at a phone book and say the same thing, all the while there is information there to be gleaned. So don't be afraid to step back form the information a little, it is really just the signs of the phase for each wire in this antenna that we are talking about here. All of those magnitudes in amps and the values of the phase in degrees is not what is important here.

In the boot, I noticed how much better that the 107" radials seemed to work on the 3/4 wave element, and I soon noticed the same improvement over my Sigma4 model when using the New Vector 4000 design. This is also when I was really able to see the radials working out of phase with the radiator, something I did not see in my Sigma4 model. I guess one could say here, this opens up an all new can of worms, right?

You might ask, which do I think is best between these two antennas? That is for another post maybe, but I do have an opinion and it might surprise you, because I have thought about that too.

 

[BOOTY MONSTER]

I dont even TRY to figure the antenna out i just put it up and talk off of it...

nothing wrong with that but we enjoy trying to figure them out . sometimes we agree , sometimes we disagree and sometimes we poke each other a bit ..... no harm no foul

 

[Marconi]

is it possible that since the cone is containing the radiation from the vertical within it and has an opposing current on the outside in phase with the remainder of the vertical that the cone makes the vertical act like it's only the wavelength of the vertical above it ??? for example on a 3/4wl version it sees the vertical length above the cone as a 1/2 wave ..... and on the taller versions the vertical above the cones ring acts like a 5/8 ? the cone does seem to behave in a few ways like coax ..... but i'm just guessing

OK, BM. Think about what you said, and then ask does the coax radiate? Remember how the Gain Master works using CMC.

Considering what we understand about coax having the potential for radiating common mode currents, then your idea has to be considered. Is that what we are seeing, CMC flowing over from the top of the hoop down the radials and radiating like real coax could?

 

[Marconi]

Has an off center fed 3/4 wave vertical antenna (fed at 1/4 wave from the bottom) been modeled and the result compared to thi antenna?
- 'Doc

I think I did that idea using NB's 1/2 wave phaser idea recently...when I extended the radiator to 5/8, and 3/4 wavelengths, but I don't remember the results. Maybe I saved the model. I'll check.

 

[Marconi]

nothing wrong with that but we enjoy trying to figure them out . sometimes we agree , sometimes we disagree and sometimes we poke each other a bit ..... no harm no foul

Hey BM, I use to have a pet doodlebug in an old mayonise jar. He use to do the same thing all the time too, just duddle around in the jar.

I let him go though. He told me life was boring doing the same thing all the time.

 

[BOOTY MONSTER]

OK, BM. Think about what you said, and then ask does the coax radiate? Remember how the Gain Master works using CMC.

Considering what we understand about coax having the potential for radiating common mode currents, then your idea has to be considered. Is that what we are seeing, CMC flowing over from the top of the hoop down the radials and radiating like real coax could?

i was thinking (could be a problem right there) along the lines of coax having 3 different currents . one on the center conductor , one inside the shield and one outside the shield . i forget their names and don't feel like hunting them down (i got a lil sick bug) . i have a coax choke on mine to minimize any CMC's that maybe on the coax . FWIU these type of antennas are more prone to CMC's than other GP's . i've wondered if the basket doesn't provide enough ground plane , if it could be modified to reduce it's CMC's without reducing it tx and rx . or what else could be causing CMC's ...... mine got into a cheap set of computer speakers and a clock radio .... could have just been proximity though .

 

[bob85]

that cst animation looks like a 5/8wave eddie, lower 1/8 out of phase with the upper 1/2wave

i agree the sleeve radiates like any transmissionline that has imbalance of voltage or current on its conductors,
to understand the sigma you need to understand how transmissionlines work and what causes them to radiate / not radiate, been parallel alone won't stop it radiating & the sigma is not parallel.

 

[HomerBB]

I was going to supply the transmission line radiation terminology, but Bob beat me to it.
I agree with the notion that the cone is radiating due to a coaxial effect.

Common Mode Currents:

"Common mode currents can flow in all sorts of systems, not just antenna feed lines. . . . In an ideal world, RF flows down the outer surface of the center conductor of the coax cable cable, and returns on the inner surface of the coax shield. When there is an imbalance in the antenna (for what ever reason), current will flow on the outside of the coax shield. This may not seem possible, but it is important to remember, unlike DC, RF current doesn't flow through the conductors, it flows on the surface of the conductors. The current which flows on the outer surface of the shield is called common mode current. In other words, it is the unbalanced current not returned within the coaxial cable.
This leads to a very important question. If the current isn't returned in the cable, where does it go? The answer is, it radiates! In fact, the amount of radiation from the coax cable is proportional to the common-mode current on that cable. This leads to another question. What causes common mode currents? Well, hopefully this article will answer that question sufficiently."

I think this applies to the Sigma/Vector antenna system. We all know among other functions, the purpose of a GP radials system is to decouple the vertical, add an element of balance to the antenna, and serve to restrict common mode currents. I do not think these radials/cone are actually ground planes functionally, but due to how they are turned up to form a sleeve, are exactly what has been said of them - a coaxial sleeve that utilizes CMC to assist in radiating while capturing the opposing phase currents on the antennas lowest 1/4ƛ within itself.

Marconi, I realize that you are looking to EZnec to supply some proof of sufficient radiation to assist in the remarkable performance some claim for this antenna. Why it seems lacking to you may be owed to EZnec not correctly supplying enough information on this antenna type. I do not know the program, so I can not say.

One thing does occur, however, the antenna behaves in the manner that supports the theory behind it.

I just can't understand the red indicator being on one side of the antenna at the top and on the other side at the bottom, but I'm like you, I see it telling me I'm seeing phasing going on. When I see phasing going on in Eznec, the red current indicators are typically represented as being on the same side, and when out of phase is going on...the opposite is occurring.

This is different from what the Sirio software is suggesting. So, I have to ask, why?

As for your question of why EZnec doesn't show the same currents that are shown by the red and blue being on the opposite sides of the vertical above and below the cone ring, it does. At least that's what I see when I look at the red current line in the EZnec models bowing out in the upper part of the antenna, crossing over the vertical near the ring, and bowing away from the vertical within the cone on the opposite side. Seems remarkably similar to me . . .

I think when you can not see something to show you what is happening, then the obvious course is to reason why/what would produce that kind of phenomenon within the known rules of that science, in this case, antenna science. What would cause it, why it happens, and how is it done. In the case of the Sigma/Vector we already have the working antennas, so reverse engineering through analysis should provide answers to a reasoning mind. We have spent lots of time doing this and so far unless the mind is closed we keep looping back to the same conclusions.

 

[kt4ye]

i . i have a coax choke on mine to minimize any CMC's that maybe on the coax . FWIU these type of antennas are more prone to CMC's than other GP's .

Coax chokes are OK if you have "a little" CMC. I have a MFJ multi-band vertical and that's what they use. But I prefer the clamp-on ferrite beads to make sure that it's the antenna that does the radiating; not the coax.

Besides, my bride doesn't want to hear sideband on the clock radio!

 

[BOOTY MONSTER]

Common-mode chokes

 

[Shockwave]

BM, what we are looking at may be right on the mark accurate, I don't know for sure. This is why I asked Shockwave if he could provide the real current and phase data that supports this graphic.

My new model of the New Vector 4000, does not indicate that the currents in the bottom radial cage are in-phase between the radiator and the radials, as others have suggested, or as I have suggested, saying earlier that everything on this antenna is in phase and thus is radiating. According to my Vector model, I was wrong.

As a result I have change my mind and I see cancellation in the area of the bottom of this antenna. I missed this in my Sigma4 model I made earlier, because the Vector, with its longer radials, shows to be far more effective in its work, and if asked I can demonstrate that too.

The radials are all noted to be in a + phase condition with each other, and their magnitudes are about equal, so they radiate as antenna currents. However, the portion of the radiator inside the radials shows a - phase condition, with an equal magnitude to the combined magnitude for the radials...so we see cancellation due to the phase difference.

The data follows and indicates how I made the comparisons: I summed the magnitudes of currents for the 1st segment in each radial. They are in a + phased condition, and when their currents are combined they = 1.0217 Amps.

The I did the same with the 1st segment of the currents in the radiator, which is in a - phase condition = 1.1326 Amps.

These five parallel elements show us magnitudes that are all about equal...which fits one aspect for the rule on radiating currents. However, when we consider the phase, we find there is a difference, and this fits the rule for cancellation. Thus there is little to no effective RF generated.

If they were parallel to the vertical radiator and this were a balanced antenna with equal currents, the cancellation rule would apply. Neither condition has been met.

That said, there may be a little RF generated however, due to the very small difference in magnitudes, and we would refer to that as common mode currents.

All I have as evidence is my model. It is available for display, and is more descriptive for what I see than the graphic model that Shockwave produced.

I will post the tabular currents log and make some notes explaining things as I see them...depicting further what is going on in my model and in the bottom of the Vector.

Again, I have requested Shockwave to consider to show me a similar data set from the software he used to produce his graphic.

Stop thinking I'm holding out on you Marconi. The only tabulated logs I have for this design are what was required by the FCC and Industry Canada and they are for the total relative field, not individual element currents. Have you considered searching online for information regarding CST to help you interpret the information it provides? I think you'll find the old analogy "a picture is worth a thousand words" fits well here. The very questions you are asking about the currents and phase on individual elements is all there. Homer is able to see blue and yellow radiation emitting from the outside of the cone. Just compare that to the chart on the right for phase and magnitude as related to color.

Now, since Shockwave has already declared that Eznec cannot model the Sigma4 design, without indicating an off-the-wall maximum high angle pattern, then all I have to counter that is...does my model display what SW suggested will happen when we try to use Eznec to model the Vector.

I'm not sure where you're getting this from Marconi. I've said many times that it is the cone on this design that PREVENTS the high angle lobe from becoming dominant on this 3/4 wave. I've also urged you to model a standard 3/4 wave with anything other then radials that sweep upwards so you can clearly see all other 3/4 wave ground planes have this lobe and sweeping the radials upwards puts more energy on the horizon.

IMO, this model does not indicate what Shockwave claims, that Eznec will show a very high angle for the maximum signal at about 43* degrees which is undesirable for CB work. He further claims that this is due to the fact that Eznec cannot model the radials at sharp angles to the radiator, because Eznec does not recognize the radials in that position, while other's claim that Eznec limitations will not allow for radials that are close together. Don't you see the radials are close together on this model, and don't you see the model is working? If an Eznec model does not work due to its critical limitations the program will stop and produce a warning pop-up message, and you cannot proceed until the issue is resolved. I have a work around for this close radial condition in the Vector model, and I will share the info.

That said, how do we answer this question without further information, which I'm willing to produce for us to consider. Plus I add the question, why don't we see my model showing a very high angle of radiation in the 43* degree area of the pattern...instead of what we see with this model?

Model what I said and you will see what I said. You can already see the strong secondary lobe around 40 degrees in your model while the lower 8 degree lobe is dominant. Sweep those radials away from the vertical radiator and watch the power shift to the upper lobe.

Booty Monster, here we are dealing with the rules that apply to radiating elements, or conversely with the rule for non-radiating elements that are due to cancellation. I am referencing antenna mode, transmissionline mode, and common mode currents to be sure.

Since the question I've asked, regarding what Shockwave's image is showing us, appears to be too difficult for anyone to speculate on, maybe we could have a discussion on what the definition for the rules on radiating elements as noted above.

Thus we see magnitudes that are about equal, but phase is different. Thus we see cancellation. If Shockwave can show me his current data, and it shows to be to the contrary to the Eznec currents, then I will concede that the Sirio antenna software shows the correct data, and without doubt the Sigma4/Vector works just as he and others state.

I've shared everything I have access to in CST Marconi. I didn't spend the $2,500 that CST costs, that was provided to me by Sirio and it contains the info regarding phase and current. When people said the one still photo wasn't enough, I asked Sirio for the entire file containing the currents through one complete cycle of drive. I'm somewhat tired of having to always come up with more evidence. My problem with EZNEC+ is unfortunately it supports the 1/2 wave J-Pole theory by missing the fact that effective radiation is taking place on the cone. I can prove 100% beyond any doubt that EZNEC is miscalculating the radiation wavelength of this antenna by 1/4 wavelength or 90 degrees too short. I've explained to Roy Lewallen himself how I've spotted this 90 degree miscalculation and he is requesting more information from me regarding my claims on these phase angles.

I intend to build him a model that is modified in such a way that it will depend on his program reporting the correct radiation wavelength for it to line up with a real working prototype. I have a feeling I will have to send him the modified prototype before he believes me over the program. I'm prepared to do that because adding just 4 wires to the EZNEC model and 4 wires to a working prototype are going to demonstrate a clear physical deference in length of more then 8 feet on this band. That's a problem when the model is off a 1/4 wave and I'd love for Roy to fix it so I can use the less expensive program and not have to buy CST. I already wasted enough money having to refile inaccurate patent documents on improvements for the design that were calculated off the EZNEC+ model rather then the working prototype that couldn't be tested until last spring. That was a disappointment.

I will post the model and the currents log soon.

View attachment 8199

Bill, also note that this model shows very little currents on the mast in the tabular currents list and the red indicator on the antenna view as well. Shouldn't have any common mode currents problems with this model at 36' high to the hub and feed point.

Detune the antenna, especially that cone away from an electrical 1/4 wavelength and watch the common mode current problems creep up in the field.

 

[Shockwave]

To tell you the truth Homer, I did just as you suggested. I started with a standard 3/4 wavelength radiator, and 4 x 107" inch horizontal radials. As anticipated, I got the typical bad looking, bad acting, high angled antenna we might expect.

Then I started raising the radials up, first at about 40* degrees, and went on up in a couple of steps...untill I got close to the slant we see in the Sigma/Vector.

I've posted about this already, and that was just recently when Shockwave suggested that I may have gone up too high with the radials. I showed him a picture of the bottom of my Vector, which I had been working on...and told him that the model dimensions were based on those that Bob posted sometime back.

In fact, it was this experience with this 3/4 wave project that got my attention on the Vector. This is when I decided to try and get it to specs too, just like I did with my Sigma4.

Homer, the point I want to make about the current log is not in all the details. Each line of information pertains to only about 3" of space on this model, and we don't get much out of looking at all the details.

Step back a little and consider the individual wires and where they are on the antenna. For and antenna maker, that should not be difficult to do. This is where I added notes, hoping it would help a little by describing the parts.

Try just considering the sign of the phase for each wire in the antenna. This is what helps us determine cancellation and radiation. The number values are basically meaningless for this discussion. Do you understand any information from the numbers referred to in the visual graphic Shockwave provided? If not, then you get my point here. If you do understand those numbers and they tell you something of value, then you are well beyond all of this understanding, and you need to be describing what you see to me, instead of me to you. I would like to see all of the numbers that support that small range of numbers though.

Back to the point, I'm trying to make regarding what is likely radiating and what is not. When the signs are all - phase, it indicates wires are in phase and radiating. When the signs are all + phase, it means things are in phase and radiating. However, when two wires have different a phase...is when we see cancellation.

This is the only point I was trying to make, and this is where I see evidence that the bottom of the Vector does not appear to radiate effectively. I posted this currents log for no other reason than to provide such info...about the phase of the wires in the Vector.

I think you indicate that you see phasing information in the Sirio graphic. I also sense you are trying to assume that there are two kinds of current on some wires, and that there is a difference between one side of an element vs. the other side. This idea has been proposed I think, but just saying the words doesn't support or prove anything but opinions, and to be sure...that is all I'm doing here too.

There may be the difference you see in this 1000 x the blink of and eye event we imagine with RF, because we are dealing with alternating currents. But man's ideas trying to visualize this is very limited, and I just don't see this image telling the real truth regarding the phase of these currents. The graphic is impressive however, and it does suggest what the author is saying I suppose, but we are trying to apply real time to an event that happens millions of times a second, and that is hard to visualize in real time. I guess my problem is trusting the words I hear from guys that like what they see and suggest they fully understand what is going on, without question. I know that is not happening, even if the text is read and understood. On the other hand the real data goes a long way in explaining what is going on. But folks have to make an effort to try and understand what folks say, or all is for naught. I'm not giving up on anybodies ideas...just because it is a hard subject to understand. Again, this is why I ask Shockwave for his help in explaining what he presents by showing us the current and phase data.

In a very general sort of way, the guys who invented the method of moments algorithms found mathematical ways of stopping and measuring currents, and their determining the results at a specific point in time. Our computers just handle the calculations for us very rapidly. This process produces a lot of data. The guys that designed this simulated feature in the software that Sirio uses is trying to manipulate the data in an interactive way so we can better visualize the events at a speed we can better understand, but information is limited at AC speeds, and we are left with the understanding of others as to what it really means and for sure what it looks like. And then the viewer applies his own twist to what he sees, and therein lies the issue I raise.

I just can't understand the red indicator being on one side of the antenna at the top and on the other side at the bottom, but I'm like you, I see it telling me I'm seeing phasing going on. When I see phasing going on in Eznec, the red current indicators are typically represented as being on the same side, and when out of phase is going on...the opposite is occurring.
This is different from what the Sirio software is suggesting. So, I have to ask, why?

IMO, either one of the software designer's probably could have designed these currents to show up either way, but they didn't. I have proof of what Eznec it showing, now I want to see what CST software current data and phase detail shows us.

Look at this pattern. Can anyone tell me what antenna this looks like is being intimated? Then tell me if this is the way you thought this particular antenna worked?

That said, my Eznec provides the tabular current list that you find so difficult to visualize and we are lucky to have both ideas to consider with Eznec. I'm just asking Shockwave if he can do the same with his software scheme. You could look at a phone book and say the same thing, all the while there is information there to be gleaned. So don't be afraid to step back form the information a little, it is really just the signs of the phase for each wire in this antenna that we are talking about here. All of those magnitudes in amps and the values of the phase in degrees is not what is important here.

In the boot, I noticed how much better that the 107" radials seemed to work on the 3/4 wave element, and I soon noticed the same improvement over my Sigma4 model when using the New Vector 4000 design. This is also when I was really able to see the radials working out of phase with the radiator, something I did not see in my Sigma4 model. I guess one could say here, this opens up an all new can of worms, right?

You might ask, which do I think is best between these two antennas? That is for another post maybe, but I do have an opinion and it might surprise you, because I have thought about that too.

Don't be confused into thinking that "one side" of the antenna is in an opposite phase as the other in CST. The difference in color between sides is so you can contrast the phase change along the length. There is no change from side to side. This is a difference in the visual interface much like EZNEC only shows current on one side of the antenna with it's single line. That doesn't mean there is only current on one side of the antenna. It's just one way of displaying the change in phase along the length of the radiator.

The visual model was not created or altered to display some desired goal either. CST inputs information much the same way as EZNEC does. You build the model to match the antenna, it provides many different areas of information. The posted model is just one thing it does. Showing not just the currents on the individual radiators, but more importantly how they propagate away from the near field and in the case of the Sigma, they combine.

With the 5/8 wave ground plane you posted in CST, it's exactly the phase angle I would expect. Anytime you have an end fed single inline radiator longer then 1/2 wave or 180 degrees of the signwave, expect phase inversion to occur at the base. The length of this inversion will continue in the base to whatever length you add to the top of the half wave all the way until you reach full wavelength where it begins to come back into a constructive phase.