[Antennas] dipole question

[Terry Conboy]

At 07:54 AM 2007-09-29, Robert Preston KC0YDZ wrote:
>what would be the effect of placing a director length wire on both the
>"front" and "back" of a dipole antenna. I assume that it would just
>tighten the two lobes?
>
>thanks
>n0nst via kc0ydz

I ran a sample horizontally polarized model in free space and it 
showed about 1 dB bidirectional gain over a dipole due to a slight 
"flattening" of the normally circular dipole elevation pattern.  The 
signal at the zenith is down about 1 dB compared to a dipole.  There 
is also a very slight narrowing of the azimuth pattern compared to a dipole.

The presence of the two directors also modifies the feed impedance of 
the dipole, depending on the spacing and tuning of the parasitic elements.

The SteppIR yagis have a bidirectional mode.  Perhaps they use this approach.

73, Terry N6RY