Roy Lewallen wrote:
One of the advantages of a Yagi is its directivity. When mounted
horizontally, its horizontal pattern is quite directional, but the
pattern in the vertical plane is relatively broad -- the vertical
pattern of a typical HF Yagi in the forward direction, in fact, isn't
much different from a single dipole. If you mount the Yagi vertically,
the two patterns swap so the horizontal pattern ends up very much
broader than when mounted vertically.

Roy, are you talking about high gain yagis? I just looked at the
beamwidths of an 11 element DL6WU Yagi on 2m and got 35 degrees
horizontal and 39 degrees vertical in EZNEC. Not much difference there.
Alan