[TowerTalk] Holy SteppIR!

[Jim Lux]

At 09:07 PM 12/26/2005, StellarCAT wrote:
>adjusting the vertical tilt of an antenna does nothing to raise
>(or even change) the radiation angle... or at least this was the
>conclusion W2PV came to in his book.
>
>g.


To a first order (and in such a complex system, this might not be valid), 
the overall pattern would be the multiplication of the antenna's pattern 
with the pattern of an isotrope at the same height above ground.  Given the 
very strong effects of the ground reflection on antennas moderately close 
to the ground (<1 wavelength),  with a low gain antenna (<10dBi) the ground 
reflection will dominate.

However, as the antenna gain goes up, the ground reflection becomes less of 
an issue, because the power radiated at the ground (and available to 
reflect) becomes less.  This will apply with both horizontal and vertical 
stacking (both of which reduce the vertical beamwidth of the antenna).

At 20dBi, a wag of the vertical beamwidth would be about 15-20 
degrees.  That's a lot narrower than the 360 degree vertical beamwidth of a 
dipole.  A lot less power directed at the ground, so if you steer that beam 
up at, say, 30 degrees, you'll get almost the full gain.

Jim, W6RMK