NEC-LIST:Yagi bandwidths

Yagis can be designed for narrow or wide bandwidths. The OWA design has
been noted. Wider bandwidths for both the source impedance and standard
operating parameters (gain, front-back, etc.) are obtainable from DL6WU
designs, for which there is a great deal of information, including an
article at my website. In my own wide-band designs, I have obtained up to
23% bandwidths in the 230-300+ MHz range with usable gain and F-B.
(Bandwidth % here means the upper minus the lower operating limit divided by
the center frequency times 100.)

Wide bandwidths depend on setting the first director at a distance from the
fed driver so that it acts as a secondary driver that dominates in terms of
relative current magnitude at the element center for the upper half (or so)
of the operating passband. Typically, the required spacing does not offer
complete control of the pattern over the entire bandwidth. The OWA uses
techniques that result in a very good bandwidth but less than the widest
(about 10% is the widest I have achieved), but with further refinement of
the second and third directors to allow good pattern control (relatively
equal gain and a very good front-back ratio) over the range. There will be
a discussion of wide-band and OWA techniques in the forthcoming issue of
QEX.

Yagis have a number of allied issues, including the strength of forward and
rearward sidelobes, the number of elements for a given boom length, etc.
Hence, bandwidth is only one of many properties that must be balanced in
determining a Yagi design that will meet a set of operating specifications.

L. B. Cebik

L. B. Cebik, W4RNL /\ * / / / tel: 865-938-6335
1434 High Mesa Drive /\ / \/\ ----)(--- http://www.cebik.com
Knoxville, TN 37938-4443 / / / \ / / || / e-mail: cebik_at_cebik.com
USA / / / \ || W4RNL_at_ARRL.org

-- 
The NEC-List mailing list <nec-list_at_gweep.ca>
http://www.gweep.ca/mailman/listinfo.cgi/nec-list