Jim Brown wrote:
>>> After studying the chapters in N6BT's book that described this technique, I
>>> spent time trying to model it, with only limited success. As I recall, I
>>> could get good coupling (both match and radiation efficiency) with two
>>> bands (one directly driven, one parasitically coupled), I didn't get a
>>> third band working. It seems intuitively obvious that while the technique
>>> is elegant and the performance of Tom's antennas prove that it works, the
>>> design is NOT trivial.
A detailed analysis of coupled-resonator dipoles may be found as the second
bullet on this page:
http://ac6la.com/aecollection4.html
Compared to a fan dipole (elements physically connected at a common feedpoint)
the advantages of a coupled-resonator dipole are 1) independent fine-tuning of
each element, little interaction between elements, and 2) with optimal spacing
it is possible to get an *exact* match to 50 ohms on the higher (parasitic)
frequencies. (The match on the primary frequency will depend mostly on height
above ground.)
The disadvantages are 1) narrower bandwidth than stand-alone dipoles and 2) the
mechanical complexity. You need to come up with a way to maintain a uniform
and relatively small separation between the elements. That's easy to do with
tubing, not so easy with wires.
Dan, AC6LA
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