Martin Brown wrote:
On 06/04/2015 10:07, Brian Gaff wrote:

Well its not a black art, all aerials still obey the same rules, its just
the compromises made in the design. I recall these were used in
millimetric
radar systems and the main reason was that they needed to be able to
steer
them electronically. Not tried the scaled up versions, I have to say.
Brian


Although they obey the same rules the complex shape of a finite depth
fractal does produce interesting resonance characteristics that may
sometimes be useful - but there is a lot trendy snake oil being sold.

Some old TV aerials were (unrecognised at the time) fractal array
designs. The Wiki article isn't bad for the OP as an intro.

http://en.wikipedia.org/wiki/Fractal_antenna

Some of the deeper theory of serious fractal antenna designs has only
been relatively recently understood (around 2000). Some very odd novel
metamaterials are based on this sort of approach too.

My money would be on log periodic though for practicality.


I'm not convinced that fractals are understood. Log periodic is a form
of fractal. The problem as I see it is that there doesn't seem to be a
calculating procedure for fractals which can optimise a design. You seem
to have to pick a geometry, then calculate a possible set of results.
Testing can be quite close to the calculation, but gain figures are
never posted. Fractals seem to suffer from lots of notches in the
response curves as a result of repeating one fixed shape. I was hoping
someone here had some hands on experience of performance.