QRZ.Com currently has a very interesting item on fractal antennas. While the idea of applying fractals to the design and construction of antennas has been around for quite some time, very few hams have actually built them, and there are currently no companies building commercial fractal antennas for the ham radio market. The question, of course, is why?
Those that are hyping fractal antennas—most notably W1YW, CEO of Fractal Antenna Systems—claim several advantages. These advantages purportedly include wider bandwidth smaller size when compared to traditional antennas, such as verticals and dipoles. Those that are trying to debunk these claims contend that this is all just hogwash, and that there’s no real scientific basis for these claims.
One thing that’s confounding this debate is that there have been very few articles published on the topic. For commercial reasons, W1YW has made his articles unavailable. He says that he will be publishing something real soon now, but it’s uncertain to me when exactly this is going to happen.
There is at least one article out there that describes the construction of a fractal antenna for amateur radio use. “FYI:FYQ: Another look at the Fractal Quad Yagi” was published in the October 1999 issue of 73 magazine. It describes the construction of a two-element, 10m antenna. Like most 73 articles, it’s not incredibly technical, though, and doesn’t really contribute to this debate, except to demonstrate physically small antennas can be made using fractal design.
Below is a photo of a 10m antenna that W1YW says that he made, just to give you an idea of what they look like.
Even this photo caused quite a bit of controversy, some noting that they thought the photo was doctored or that they didn’t think that the antenna, as pictured, could really work as claimed.
What’s interesting is not so much the antennas themselves, but the personalities on both sides of the fence. The discussion quickly devolved into a flame war, with neither side scoring a knockout.
Personally, I think the brouhaha is much ado about nothing. It seems to me that it’s been demonstrated that you can build antennas using fractal design techniques. They are physically smaller than traditional antenna designs, but you really don’t get something for nothing. Overall, they don’t have as much gain as yagis or quads, and they’re more complex to build.
If W1YW can build antennas that radiate a signal and can sell those antennas to someone, then more power to him. In the end, his company will live and die by how well, his antennas work and how much they cost when compared to antennas from other companies.
Fractal antennas are discussed in “Small Antennas” (Volakis, et al, (C) 2010 McGraw-Hill) as a special case of the more general “meander line” antenna. Work to date suggests they are not a magic bullet. The effect is basically just a means to add more distributed capacitance and inductance in a somewhat unconventional manner. They still suffer the same effects of low radiation resistance and high Q (narrow bandwidth) as other electrically small antennas, and their longer wire lengths lead to increased conductor loss.
Much more promising are approaches based on slow wave, volumetric and meta material techniques. Working prototypes as small as 1/50 lambda have been demonstrated at cm wavelengths with efficiencies and bandwidths comparable to a full size dipole. Unfortunately, all require patches or detailed geometry that would be difficult and unwieldy to duplicate at HF wavelengths.
Fractal antennas are not new. The definition of what type of antenna geometry is fractal remains somewhat fuzzy. It is now “in” to say that n antenna is fractal, but that can’t make all antennas fractal. If you look at the turnstile antennas that had been used by commercial VHF TV broadcasting stations since 1940s, you will see that the vanes of those antennas are wavy;in order to be broadbanded for a 6 MHz bandwidth, the vanes are what I consider to be first order fractal.
Fractal geometry means using a clover leaf or snow drop pattern rather than a loop or a square. Fractal geometry may also involve successive branching of antenna elements according to some fixed ratio.
Everything that looks fractal is not an antenna.
Every antenna is not fractal.
While printed fractal antennas may be highly advantageous for low powered microwave cell phones, they may not be advantageous for 6 Watt 2-Meter ham HTs. While fractal antennas may prove to be superior to HF antennas that use lumped constant loading coils or capacitors, they can not be expected to be as efficient as full size dipoles. Forward antenna gain must in any case be the result of antenna main lobe patterns. There are many compromises to be made. Small aperture antennas can be a compromise only when space is limited.
See also the many posts on this subject at QRZ.com
73, Bob w2ilp
Since you hot-linked the photo from another site, I can’t see it. The proper way to do this is to ask for permission to post a copy of the photo. I am very interested to see what it looks like. I don’t believe the hype – I’m working on TV antennas, and fractal is the latest fad, but I don’t think the numbers really work out. People talk a lot about theory but I don’t see anybody posting the hard data, so their talk is pretty meaningless. I would love to build a couple fractal designs and test them.
But yes, in my research I have found that most of the “information” about fractal antennas seems to come from one source and I think that source might be a little biased. He almost suggests I would be violating the law if I built a fractal antenna myself. I don’t like that!
Interesting. He must have taken down the picture. I doubt that he would have given me permission to publish it here.