Post below from May 20, 2004

Wouldn't a "non-radiating" feedline in the field of a radiator also distort
the patterns of that radiator? Any conductor can do that, even if it is not
a feedline. NEC-2 models of FM broadcast transmit elements (and test range
patterns) show this clearly.

Paper 6 at http://rfry.org shows the free space patterns that the element
arms of a rototiller FM broadcast transmit antenna develop if they could be
driven from internal power sources -- and then the effects of adding the
element stem, mounts, feedline, and some nearby tower structure. The
patterns can get very skewed, even though the only radiators getting power
via a metallic path from the tx are the element arms themselves.

RF
____________

"Roy Lewallen" wrote
With a typical ground plane antenna, the feedline can radiate
significantly, distorting the pattern. This effect could easily be
different for the different antennas. Modeling indicates that two baluns
are often needed to suppress the current on the outside of the feedline.
A model which includes the feedline might give some insights as to why
the antennas behave so differently.