"Bob Haberkost" wrote
One of the issues with most FM arrays with gain is that, for many,
the spacing which results in the array having gain also results
in a fairly pronounced hot-spot directly above the antenna,
where few people would be expected to be, as well as
directly below...
_________________

This is true only when each element in the array has high relative field at
+/-90 degree elevation, and the elements are vertically spaced about one
wavelength apart. Shorter vertical spacings reduce such radiation from
these arrays. Using 1/2 wave spacing reduces it to a theoretical zero at
+/-90 degrees elevation (the zenith and nadir).

BUT, the great majority of FM broadcast transmit elements used today have
elevation patterns with very low relative field at +/90 degrees. An array
of such elements also has low relative field at +/-90 degrees -- even with
elements spaced at one wavelength intervals. IOW, no hot-spots above and
below the array.

Patterns of four element types in common use today, and an elevation pattern
for a 6-element, 1-wave-spaced array of one type are included in the PDF
slide show listed as Paper 10 at http://rfry.org.

RF