"Dave" wrote in Art's Yagi thread:
... believe me, many phd's have made their life studies of reducing
that last little bit of radiation off the side or back, and the conclusion
is??? you can't do it.
_________________

Just to note that an inline array of radiators spaced 1/2 wavelength apart
and fed with equal phase, but binomial power distribution produces a
radiation pattern with zero sidelobes, and an infinite front-back ratio.
These designs are shown in chapter 5 of Kraus' "Antennas for All
Applications," 3rd edition.

Such antenna arrays have been marketed by FM broadcast antenna OEMs to
reduce the power density (radhaz levels) on the ground around towers with
high power FM systems on them.

RF

Read the chaper again... That is an inline array of point sources... A
different kettle of fish from an inline array of real, physical
antennas... Now, you may approximate this stellar performance by going
to very short radiators with capacity hats on the ends, etc. so that
the current distribution across the radiator approximates linear, but
the price you pay in matching the source and feed line to these near
point radiators ought to keep you busy until you meet the requirements
for social security... These are not what I would consider efficient
antenna arrays...

Such antenna arrays have been marketed by FM broadcast antenna OEMs to
reduce the power density (radhaz levels) on the ground around towers with
high power FM systems on them.

Gosh, I don't see CushCraft offering any such arrays for 80 meters - I
sure could use one!!!

denny / k8do

"Denny" wrote in message
Read the chaper again... That is an inline array of point sources...
A different kettle of fish from an inline array of real, physical
antennas...
___________

The example in Kraus showed isotropic radiators, but the same zero sidelobe,
infinite F/B descriptors for the array pattern apply for any pattern shape
generated by the individual radiators, as long as they are the same.

The FM broadcast antennas I referred to use standard FM c-pol elements fed
as I described, and have these characteristics -- except for re-radiation by
the tower.

Set up a simple NEC model using dipoles, and check for yourself.

Or you can look at mine in paper 10 at http://rfry.org

RF

"Richard Fry"
The example in Kraus showed isotropic radiators, but the same zero
sidelobe, infinite F/B descriptors for the array pattern apply for any
pattern shape generated by the individual radiators, as long as
they are the same.
_______________

I need to correct myself. As applying to binomially-fed FM broadcast
arrays I should have written infinite max-min ratio, not infinite F/B ratio.

RF

Infinite F/B ratio? I get the impression that we're talking about a
multi-bay FM antenna that should be omnidirectional in azimuth... Do
you mean infinite horizontal to zenith ratio? Or Front-to-Side ratio
if it were installed horizontally? Maybe I'm missing something. I
guess I'm missing Kraus's book! We're not talking a unidirectional
beam here, right?

A 5x5 planar dipole array with a 2:1:1:0.1:0.1 ratio spaced on a 1/2
wavelength grid gives a nice clean bidirectional beam with "no"
sidelobes.

A pair of these arrays spaced 90 degrees and fed 90 degrees makes a
nice unidirectional clean beam with good F/B and low rear lobes, and no
front sidelobes.

Not envious of someone who tries to build a distribution harness for
this thing, though.

http://www.n3ox.net/projects/eznec/dipole_array_144.ez

73,
Dan

Sorry Richard, I started composing the message, then I started modeling
the antenna, then I finished the message and found your correction ;-)

73,
Dan

Yeah, there is a lot to be said of the pony express days where you had
weeks to think between replies... I put my keyboard in my mouth quite
often...

denny / k8do

wrote:
Sorry Richard, I started composing the message, then I started modeling
the antenna, then I finished the message and found your correction ;-)

73,
Dan