Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

   Home   Help Search  
Pages: [1] 2 3 Next   Go Down
  Print  
Author Topic: Fractal antennas for Ham Radio  (Read 37775 times)
AC6IJ
Member

Posts: 56




Ignore
« on: December 16, 2010, 11:07:02 AM »

Does anyone know if there has been any design of fractal antennas for ham radio and is there plans for such?
 I have seen designs for Cell phones and am wondering about the design for ham radio. Tnx Bill
Logged
WB6BYU
Member

Posts: 13353




Ignore
« Reply #1 on: December 16, 2010, 11:41:17 AM »

Yes, they have.

Dr. Cohen had a design in QST showing a fractal 2-element quad for 2m.  But I don't think they
have gotten a lot of attention because there isn't much profit margin in ham antennas and the
fractal designs don't necessarily work any better than simpler options for many ham
applications.
Logged
N3OX
Member

Posts: 8847


WWW

Ignore
« Reply #2 on: December 16, 2010, 11:42:05 AM »

Chip Cohen, W1YW (ex-N1IR) who has a fractal antenna company (http://www.fractenna.com/) had some designs for a shrunken 10m quad on his website but I don't think those are available anymore.  

If I recall correctly, the elements were something like this:

http://n3ox.net/files/it3.jpg

I could be remembering wrong though.

I think self-similar antennas (log-periodics are a very old type) have their best applications in very wide-band applications.  Ham radio isn't really one of those, because we have several narrow bands to cover, though sometimes people just like to have a wide band antenna (like a log periodic)  I haven't seen a lot of experimentation.  I think commercial manufacturers would probably have to get licenses from Fractenna.  I don't know if there would be any particular advantages to fractal elements but some of them are easy enough to try at home.
« Last Edit: December 16, 2010, 11:44:16 AM by Dan » Logged

73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
N6AJR
Member

Posts: 9912




Ignore
« Reply #3 on: December 16, 2010, 02:37:17 PM »

THE FRACTAL ANTENNAS ARE VERY BROADBANDED. tHIS IS WHY THEY NOW USE THEM IN CELL PHONES, AS THEY CAN DO PHONE, INTERNET AND GPS ALL ON THE SAME ANTENNA. 
Logged
AA4HA
Member

Posts: 1495




Ignore
« Reply #4 on: December 16, 2010, 03:55:13 PM »

A spiral log periodic HF antenna would be very cool;

http://ascsignal.com/files/hf/omin_directional/3000.pdf

I can see where a fractal antenna could work for VHF+ frequencies but it would be the size of the state of Connecticut at HF.

Tisha
AA4HA
Logged

Ms. Tisha Hayes, AA4HA
Lookout Mountain, Alabama
N3OX
Member

Posts: 8847


WWW

Ignore
« Reply #5 on: December 16, 2010, 04:08:12 PM »

Yep there's no getting around size/efficiency/bandwidth tradeoffs, no matter how clever the antenna is.
Logged

73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
AC6IJ
Member

Posts: 56




Ignore
« Reply #6 on: December 16, 2010, 06:42:32 PM »

Hi Tisha,
        Thats strange that you would say that, I was under the impression that fractal antennas were so much smaller than full size antennas for certain frequencys. Bill
Logged
AC5UP
Member

Posts: 3908




Ignore
« Reply #7 on: December 16, 2010, 07:02:06 PM »

Over 10 years ago I followed the concept of fractal antennas and concluded they are far more practical at UHF and microwave than they will ever be for HF. The construction becomes orders of magnitude more difficult as iterations are added, and the iterations are what makes the fractal intriguing.

Each circuit element (leaf on the branch of a branch for lack of a better description) is an L/C tuned circuit and at microwave frequencies a fractal patch etched on a PC board can have hundreds of leaves on dozens of branches. Imagine each one tuned to a discrete slice of spectrum with some overlap from one to the next. Not only does that make the array exceptionally broadbanded, but at any given frequency there can be multiple elements in play and that may add gain. Conventional designs tend to offer bandwidth or gain but not both. A fractal patch also has an advantage in package density in that almost every part of a fractal radiates. Considering how small wireless devices need to be the efficient use of space is a very useful property.

In the late 1990's Chip Cohen tended to oversell the advantage of fractals and gave the impression they could scale to any frequency... IMHO he hurt the concept by hyping it as a potential wonder-tenna for HF, which it could be if it was possible to build them reliably, but it wasn't. He released a design for a 10 Meter version that I couldn't make heads or tails out of and I suspect I wasn't alone in that. He drew one corner of the antenna and we were to assume it was mirrored three times over. The element dimensions were given as multiples of a seed number and it wasn't clear how the seed was calculated. Let's just say that Chip was very guarded about the nuts & bolts of his designs and at times had trouble explaining why a fractal would be worth the effort to build...

BTW: He used to be active on QRZ.com and some of the threads saw some very "energetic" discussion about antenna performance claims.  Wink
Logged

Never change a password on a Friday                
N3OX
Member

Posts: 8847


WWW

Ignore
« Reply #8 on: December 16, 2010, 07:50:31 PM »

Hi Tisha,
        Thats strange that you would say that, I was under the impression that fractal antennas were so much smaller than full size antennas for certain frequencys. Bill

Some designs are, Bill, but fractals don't solve all the problems of small antennas. 

Here's a relevant quote from the Fractal Antenna Systems FAQ:

Q: If a FEA shrinks an antenna, how can it still work well?
A: It is well known that physical limitations impose severe field strength restrictions on electrically small antennas. And, when FEA are chosen to be very small (compared to a wavelength) they perform poorly—like all such small antennas. However, at the top side of the electrically small regime (say shrunk 2-4 times) FEA perform extremely efficiently and practically exceed other methods of antenna loading, including top loading.

There is a lot of interesting research going on.  Keep an eye on metamaterial-based antennas.  But don't buy anything from someone who's selling yet Grin
Logged

73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
WA8MEA
Member

Posts: 264


WWW

Ignore
« Reply #9 on: December 17, 2010, 01:27:16 PM »

This past week, I was surfing the channels and came across PBS NOVA.  This weeks episode was about fractal geometry.

I IMMEDIATELY put the remote down to watch this program since I recall a young ham by the name of Chip being knocked around and beat up on Usenet back in the 1990's because of his fractal antenna theories/designs.  Some of these lids were unmerciful to the poor guy.  However, Chip always carried himself VERY professionally in responding to these Usenet attack dogs.

So I'm watching the program, enjoying the mathematical, geometrical, computerization and artistic concepts of fractals....when lo and behold....they mentioned Chip on the program!  Then suddenly he appears in an interview and I immediately thought; "They laughed at Galileo, too!"

I see some folks still won't give up on the scientific principals of fractals.  Hang it up, boys!  Chip was right....whether it's HF, VHF or UHF!  Fractals are being used in ALL phases of communications!

I always like a story where the one being bullied wins in the end......

BTW, little did I realize that my 160 meter "dipole" is more fractal than dipole.  I have it in bent into the shape of a star....allowing it to fit on my lot, with very minimal SWR.

73, Bill

http://www.pbs.org/wgbh/nova/fractals/

http://www.qrz.com/db/w1yw

http://www.fractenna.com/whats/whats.html
« Last Edit: December 17, 2010, 01:30:26 PM by Bill Lauterbach » Logged
G0GQK
Member

Posts: 634




Ignore
« Reply #10 on: December 17, 2010, 02:14:19 PM »

Simple question. Who these days needs a monoband antenna on HF ? If somebody did develop such an antenna it would be expensive. Would you buy an expensive HF  monobander ?  Would anybody else buy an expensive HF monobander ? That's why the fractal antenna stays just a nice idea.

G0GQK
Logged
N3OX
Member

Posts: 8847


WWW

Ignore
« Reply #11 on: December 17, 2010, 03:11:38 PM »

I IMMEDIATELY put the remote down to watch this program since I recall a young ham by the name of Chip being knocked around and beat up on Usenet back in the 1990's because of his fractal antenna theories/designs.  Some of these lids were unmerciful to the poor guy.  However, Chip always carried himself VERY professionally in responding to these Usenet attack dogs.

I would encourage others to seek out the Usenet conversations in question and form their own opinions on who was being bullied, because I don't think it was so simple as "unmerciful lids" picking on Chip.   There WAS a lot of uncritical doubt that the concepts would work, but the whole "political" situation was pretty complicated.  

Quote
some folks still won't give up on the scientific principals of fractals.  Hang it up, boys!  Chip was right....whether it's HF, VHF or UHF!

I'm still not convinced that there are big practical advantages for HF.  If you watch "FIRST VIDEO – OUR AMAZING FRACTAL TECHNOLOGY" on the third link you posted, it seems quite encouraging.  Pop on a sleeve, and the antenna gets better!  Cool!  But think about the thing you'd have to build to make it work at HF.  Let's imagine applying the technology to a popular ham antenna: the 43 foot monopole.  It could sure use some help to achieve a low-loss wideband match and elevation pattern control (what the metamaterial cloak does).

The sleeve they slip on would probably be ten feet in diameter and, of course, more than 43 feet tall.  I don't know if the foam part is necessary for the metamaterial to work.  If it is, a cylinder of the proportions shown in the video and the density of styrofoam would clock in at about two and a half tons if it was big enough to cloak a 43 footer.  If you don't need the styrofoam (in other words, it can be close to the dielectric constant of air) and you don't need the dielectric substrate, you need to figure out how to support a fairly precisely dimensioned fractal pattern in free space.  This was what the 10m fractal quad was... bent wire.  That works fine, but to get it arranged on a ten foot diameter cylinder surrounding your 43 foot monopole?  Difficult.  For VHF/UHF you can do printed-circuit stuff.  That's not possible at HF.

The question I still have about these things is: "is it worth it?" for HF.  Certainly a military installation could build one.  Maybe it would be worth it to them, replacing a discone with something that had higher gain and a better match and could operate on any frequency.  

A more focused question in this thread is whether there's much use for fractals for ham applications at HF?  If I want to perform an efficient match to my 43 foot monopole and make the radiation pattern better.  Should I even think about building a fractal metamaterial cloak?  Or should I just slice the sucker up and put some high quality traps in it?  I think either way, it's me who has to do the design work and construction.  Just thinking about the mechanical construction realities tips the balance toward the trap vertical.  I don't need something that covers 3-30MHz continuously.   Just our little slices, plus a little extra either side for weather-induced changes.

I also want to steer clear of testing whether or not the U.S. courts would uphold a noncommercial research exemption for patented technologies.   I don't have to worry about that with a trap antenna.  I can go ahead and build the thing and publish build details on my website so that other people can duplicate it without design work.  Can I do that with a fractal metamaterial cloak?  I don't really know, but I can tell you that I'd probably hire a lawyer to help me figure it out in this particular case.  

So on one hand, it would be really cool to put up some ropes around your 43 footer, dangle some bent wires around it, and all of a sudden have several dB more gain and a flat match to 50 ohm cable from 3-30MHz.   That's the killer app for a lot of hams. On the other hand, if it requires 1mm construction tolerances on free-space bent wires all over a ten foot diameter cylinder, two and a half tons of styrofoam, or anything like that, what good does it do hams (or any HF users who actually have ceilings on their budgets)?
« Last Edit: December 17, 2010, 03:18:59 PM by Dan » Logged

73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
N6AJR
Member

Posts: 9912




Ignore
« Reply #12 on: December 18, 2010, 01:53:20 PM »

That show was actually filmed in 1998 I belive.  Chip used to get on here quite often and was eventually harassed enough to no post any more. The Man is running a successful company doing fractal antenna design and so on, he has a degree and is quite capable.

Fractal antennas ( fractal, of any use) are most always a repeating design and the sam regardless of size.  Look at a tree, a big trunk with several branches, starting about a third of the way up.  then each branch is a smaller trunk with smaller branches  starting about a third of the way up the branch, which hodls smaller branches and smaller branches etx, but still similar and not size dependent. a tree is an example of a fractal.

so a small design like a star shap repeating smaller and smaller is a very large line when srteached out flat.
Logged
G3RZP
Member

Posts: 4742




Ignore
« Reply #13 on: December 19, 2010, 12:29:22 AM »

Chu's theory about antenna size and Q hasn't been disproved yet. In 62 years of antenna work.  A small antenna means a high Q (neglecting the resistive losses), and if you figure the definition of Q as energy stored over energy lost, the 'lost' energy is radiation. So it comes down to volume, which is why the fractal antennas don't get too small.
Logged
STAYVERTICAL
Member

Posts: 875




Ignore
« Reply #14 on: December 19, 2010, 01:13:51 AM »

The whole concept of broadband antenna's should be a moot point these days.
We are still thinking in terms of 1970's technology when we had to wrangle the antenna to get close to the impedance of the transceiver.
The military, who need reasonable efficiency in broadband applications use simple whips or verticals with an automatic antenna tuner at its base.
I have been using a vertical (or even a balanced non-resonant dipole) with a remote ATU for years with great results.
Why play around with trying to resonate the self inductance and capacitance to ground of an elevated wire, when a simple remote ATU and a press of the button will give total HF coverage, and probably 6m as well?
If you want a really proven broadband antenna, think Log Periodic or Terminated Rhombic, otherwise a remote atu with whatever wire you can hoist will work better than any other "magical" or trick antenna.

For goodness sake it's 2010, just press the ATU button on your transceiver and forget it.
Logged
Pages: [1] 2 3 Next   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!