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.

A vertically mounted Yagi is vertically polarized, and vertically
polarized radiation reacts differently with the ground than horizontally
polarized radiation. So rotating a moderately or very high yagi from
horizontal to vertical will result in loss of low angle radiation unless
your ground is very highly conductive.

These effects can be very easily be seen by modeling.

Roy Lewallen, W7EL

John Ferrell wrote:
Why do we always mount our HF Yagi's in the horizontal plane?
Antenna maintenance would be much easier for those of us with tilt
over towers if the antenna were in the horizontal plane when down for
maintenance!

John Ferrell W8CCW

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

Alan Peake wrote:

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


No, I'm not. The OP specified HF, so I'm talking about Yagis of up to 5
or 6 elements or so. Ones with a larger number of elements would
significantly narrow the pattern in both planes. I'm surprised that the
beamwidths approach about the same value, but I haven't done much
modeling or any measurement of Yagis with a large number of elements, so
I'll believe it.

Roy Lewallen, W7EL

Roy Lewallen wrote:
Alan Peake wrote:

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


No, I'm not. The OP specified HF, so I'm talking about Yagis of up to 5
or 6 elements or so. Ones with a larger number of elements would
significantly narrow the pattern in both planes. I'm surprised that the
beamwidths approach about the same value, but I haven't done much
modeling or any measurement of Yagis with a large number of elements, so
I'll believe it.


Here's a sort of intuitive approach to the conceptual analysis...


Consider the overall pattern to be like that of a phased array where you
multiply the pattern of an individual element by the pattern of the
array assuming that the elements were isotropic. Indeed, in a Yagi, not
all the elements are excited equally, but bear with me..

So, in a 3 element antenna with a gain of, say, 5dBi, you're getting
about 2 dBi of gain from just the dipoles, and 3dBi of gain from the
fact that you've got 3 elements in an array. The beamwidth is going to
be a combination of the array pattern (which is the same in vertical and
horizontal planes) and the element pattern (which is not)..


In a higher gain antenna (say 12dbi), you've got the same element gain
2dBi) but the array pattern gain is now 10dBi, so the shape of the
latter will dominate.

Alan Peake wrote:


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



I think he's talking about lower gain (e.g. a 3 element beam for 20m),
where the 3dB beamwidth might be about 50-60 degrees in the Eplane
(parallel to the elements) and 80 degrees in the H plane (perpendicular
to the elements). The 80 is about the same as the 3dB beamwidth of a
dipole.

For higher gain antennas (e.g. your VHF/UHF), the beamwidths will be
pretty close in E and H planes. (since a larger fraction of the overall
antenna gain comes from "array pattern" gain rather than the individual
"element patterns")


Of course, the polarization sensitivity of the ground reflection makes
the horizontal antenna usually a winner overall.

The EZNEC5 model that I did left me with the feeling that my model was
too vague.
John Ferrell W8CCW

On Sun, 13 Jul 2008 00:59:30 -0700, 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.

A vertically mounted Yagi is vertically polarized, and vertically
polarized radiation reacts differently with the ground than horizontally
polarized radiation. So rotating a moderately or very high yagi from
horizontal to vertical will result in loss of low angle radiation unless
your ground is very highly conductive.

These effects can be very easily be seen by modeling.

Roy Lewallen, W7EL

John Ferrell wrote:
Why do we always mount our HF Yagi's in the horizontal plane?
Antenna maintenance would be much easier for those of us with tilt
over towers if the antenna were in the horizontal plane when down for
maintenance!

John Ferrell W8CCW