In message K3B1e.8558$NW5.7100@attbi_s02, "
writes
As gain increases with a yagi design the forward
lobe narrows . With high gain yagi's the lobe
becomes so narrow it is deemed to be a hinderence
instead of an advantage. To overcome this perceived
problem one has to know what causes it.
So to the gurus of this group, what actualy creates
the narrowing of the forward lobes ?
End effects perhaps!

My tuppence worth

It is a fundamental energy conservation effect.

There is an invariant A * Omega , where A is the capture area of the
antenna, proportional to gain and Omega is the solid angle of the lobe.

So as A goes up, Omega must come down.

One way to reduce the effect is to use a number of vertically stacked
low gain yagis. The lobe becomes narrow in the vertical plane , but
remains broad in the horizontal plane. This is fairly common technique
for VHF/UHF contesters, where a narrow horizontal beam can cause missed
contacts

Brian

--
Brian Howie