Howard wrote:
On 6 Feb 2005 18:10:11 -0800, wrote:
snip
It was an unusual use of the YO
program, in that we used two reflectors
and NO directors, to get the shape we
wanted. We actually couldn't use the
optimizer, because it would actually
try to narrow the beam too much.
Remember that you must keep the
pattern about 180 degrees, and the F/B
ratio should be no more than about 11 dB.
Slick
Slick,
Could you explain the use of two reflectors? I've heard that if you
are building a two element yagi it's best to use a radiator and
reflector but haven't really learned anything about using more than
one reflector. Have seen antennas that use 3 reflectors, but they
were mounted perpendicular to the plane of the elements and there
were
several director elements - if memory serves me it was Cushcraft that
did that. Haven't seen them added behind the first reflector and am
curious as to what characteristic of the antenna's performance it is
meant to enhance.
For this particular design, it was
required in that we needed something with a
180 degree pattern, and not to much F/B
ratio. I can't tell you much more other
than we had to manually tweak the variables
to get a decent result...we couldn't use the
program's optimizer, it would have made the
forward lobe too small.
So what ends up happening in the program,
is that you end up using two directors, but
in the H-plane the lobe goes to the rear (see
link). So in essence, you flip the whole
deal around, and your two directors are
actually reflectors. Interesting, eh?
Slick