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Fractal Antennas more efficient?
Mike Hicks writes "Scientific American has a short article talking about fractal antennas. They can be 25% more efficient when used in place of the stubby antennas on cellular phones. An antenna that's fun to look at -- who'd a thunk it? "
If a fractal antenna works more efficently.. wouldn't a Pyrimid who's 4 sides consisted of the fractal designed antenna work even more efficently in all directions? The way the atenna is now.. it would function like that in a directional finder.. where when the side of the atenna is pointing to the transmitter or receiver.. the signal would be weak.. and when the broadside is facing.. it would be strong. By making it more of either a 3 or 4 sided pyrimid.. you'd have more surface area receiving the signal at one time.. allowing for a better reception at all sides and therefor a longer distance of receiving a clear(er) signal.
Ron Rossman
rjr162@psu.edu
UGrad Student in the College of Engineering
Penn State University
I talked to a friend/collegue here at work, and here is what he said:
.. far too big and battery hungry for a handset using todays technology. Mobiles in any case require 360 degree coverage .. you can have a handset lying down standing up, in any orientation you like relative to the RBS (base station)
...(or your head) ... not smart and you would loose MANY dB ... most of the power. which removes
... IF we were using very very high frequencies. But a practical
" As is common in the US, companies sometimes make a big noise about stuff that has been known for (almost) forever. As even mentioned in the article, random and regular layouts are both tradidtional for phased array antennas,
but other layouts are also used and their characteristics are known.
However there are a number of HUGE problems before you can bury such an antenna in a handset as they suggest tand the (prototype) phone shows.
1) array antennas only effectively transmit at 90 degree to the surface. If you add it some electrical tilt this can be extended to approx a 45 to (extreme) 60 degree eitehr side of that but the circuitry to do that dynamically is VERY complex
2) That energy would need to go through your hand
the point
3) actually you can't build a phased array that small in any case, the article is just "science fiction" in the sense that it is theoretically possible
problem is that you can't have the elements of the array signigicantly closer together than a wavelength, otherwise they just couple togetherand dont act independently (and the array therefore stops functioning as an array, it just works as one antenna). a 900 MHzsignal has approx a 30cm wavelenth.
So that's that!
An antenna radiates some (or most) of its energy, and sends the rest back toward the radio. This ratio is what we call SWR. Of the returned energy, some might be lost in the feedline. The rest reaches the radio and bouces back to the antenna for "another try".
If we have feedlines that are relatively long for the frequency, we get concerned about the SWR so that our energy is not wasted heating up the coax between the radio and the antenna. If our feedline is short, then the SWR is a factor if it raises the voltage high enough that the reflected energy bothers the radio. That can be really exciting if you are looking at hundreds of watts, but should not be a factor with the low power levels we are contemplating here.
So if our feedline is short enough, as is common with handheld radios (and cellular phones are radios, of course), our antenna is going to be radiating nearly 100% of the power. It is like the "efficiency" of an electric heater - an electric heater is ALWAYS 100% efficient.
Perhaps the authors really mean that their antennas can direct the radio energy in a more useful direction, such as horizontally. Often this is exactly what we want, and we already have antennas made just for this (such as a vertical dipole). If this is what they are getting at, I did not see this in their report.
A dingo ate my sig...