"John Doe" wrote in message
...
I am looking for the construction article "FRACTAL Antenna for 10m" that
appeared sometime ago in I think either QST, Ham Radio, or 73 magazines.

I have a lot of spare time on my hands - so I thought I would like to
construct one and use it portable as I live in a Antenna Restricted
Community.

73's

As others have mentioned, several articles appeared in various magazines
about the design of fractal antennas. The basic idea is to fold a standard
length of wire using a fractal pattern so that it fits into a smaller space.
One solution I saw was to wind a wire back and forth across and along a
plank of wood using pins or slots cut in the wood to support the turns.
Taking a four inch wide piece of wood around eight feet long and winding
equispaced turns you could easily fit 24 feet of wire along the plank.
__ __ __
|__| |__| |__| | Using a pattern like this.

Other more complex or even three dimensional designs can fit more wire into
a given space.

Older interpretations of antenna theory predicted that the interaction
between the closely spaced wires would effectively short out the turns and
you would end up with the equivalent of an 8 foot length radiating element
rather than the 24 feet of wire wound along the plank of wood. While there
is interaction, the apparent reduction in radiator element length is not as
bad as was predicted. So fractally wound elements can be worth the effort
where space is at a premium.

It is significant that the majority of development work into these antennas
has taken place for frequencies above 1Ghz. Main applications include mobile
phones, RF ID tags, security and remote sensing tags. At Ghz frequencies,
exotic patterns can be easily etched onto circuit boards at minimal cost.
Koch snowflake like fractal patterns combined with circular whorls seem very
popular with commercial manufacturers. A google search will reveal quite a
few pictures of what is being produced.

It is not necessary to try and duplicate the complexity of professional
designs. The main criteria seems to be to keep the wires as evenly spaced as
possible, hence the width of the winding should be approximately equal to
the linear step along the plank of wood or whatever support frame you are
using, i.e. 4 inches up, 4 inches along, 4 inches down, four inches along, 4
inches up, etc. etc.

As you will doubtless appreciate, this is similar to a three dimensional
coil being wound on a former. Because the fractal winding is flat, there are
fewer inductance effects.

Obviously fractal antennae are designed for a specific frequency or band,
but the type of winding pattern and spacing have an effect on the bandwidth.
Obviously you will need two mirror image windings to create a dipole
antenna, ideally as closely matched in dimensions as possible. Efficiencies
can approach 50% of a full sized radiating element.

Hope this helps

Mike G0ULI