# What is this antenna called, and what does the polarization and radiation pattern look like?

I was searching for helical antenna designs and stopped here to look around when I saw this antenna (below). I am guessing it has a somewhat omnidirectional characteristic that would be advantageous to put on a car/plane/'copter to communicate with a helical "command station" antenna which can be manually pointed back.

• What is this antenna design called?
• What does the radiation pattern look like in three dimensions? Is it somewhat similar to a vertical dipole with isotropy in the horizontal plane and nulls at the top and bottom, or is it substantially different?
• What about polarization - linear? circular? azimuthal? mixed?

I've tried a translation, but it does not seem to describe the antenna itself. These can also be seen at the extreme left of the second image.

• It is clearly intended to be circularly-polarized. That means it sacrifices radiation at all the specific angles in order to cover many. In other words, it would probably work equally well with horizontal as well as vertical receiving antennas. This is similar to how FM radio broadcasters do it. It is a compromize in order to cover the widest variety of receivers, at the expense of range. On FM that is no problem because they just pump a lot of power into them or add antenna bays. This one is set up vertically, but they often hang off the side of towers to cover specific directions. – SDsolar Jul 1 '17 at 8:59
• @SDsolar "clearly" because why? In what way is this clear? Clear to everybody? Is there some way one can tell by looking at an antenna that it is or isn't circularly polarized? Can you tell if the antenna in the question is right- or left-circularly polarized clearly as well? – uhoh Jul 1 '17 at 9:13
• Clearly - because of the shape and arrangement of the elements. They are generally curved instead of straight, and not all in one plane.. When you say right or left you are likely thinking about satellite antennas built like a helix where the whole thing is built to twist in one direction. But an antenna like this is both, as you can tell by the shape. Do some Googling about FM broadcast antennas and you will see that they are more like this example. The whole idea is to make it easier for the listener by removing their polarization considerations. – SDsolar Jul 1 '17 at 16:44
• @SDsolar Sorry, you are saying that this antenna is both right-hand and simultaneously left-hand polarized? I don't think any amount of googling can reconcile that. Can you show any existing evidence of a roughy omnidirectional antenna (within a horizontal plane) that transmits simultaneously equal amounts of power in both circular directions, that isn't actually just radiating linear polarization? I think it's not mathematically possible, and I don't think you will be able to find any. – uhoh Jul 1 '17 at 16:53
• @SDsolar thanks, that's the link in the accepted answer where the benefits of rejecting one CP sense is discussed, for example to reduce sensitivity to reflected relative to direct signals. In that case by about 10 and 12 dB at 1.3 and 2.4 GHz. I think FM broadcast is sometimes polarized in both linear directions (with a phase lag) to make a single circular polarization, so that FM receivers (with typically linearly polarized antennas) will receive a signal with fewer dropouts caused by reflections and rotations along the path. – uhoh Jul 2 '17 at 3:00

• Yep that's it! In order to make the answer more robust against linkrot, could you consider at least mentioning in the text that the polarization is circular, and the pattern has the same donutnessitude (I'm sure there is a better word) as a vertical dipole, but does not fall of near the axis until $\theta$ is much closer to 0 or 180°? Thanks for the speedy answer by the way! – uhoh Apr 29 '17 at 9:40