As a discussion point, consider 1/2-wave parasitic radiators sometimes
positioned within a foot or two of FM broadcast transmit elements, to
"shape" their patterns. This is the common technique used in "sidemount"
antennas that must meet FCC requirements for directional FM broadcast
assignments.

A parasitic itself is suspended mechanically in space by a non-metallic
support. It has no direct connection to the transmitter, and no conductive
physical path to any part of the antenna, its feedline, mounts, or
supporting structure.

Such parasitics do affect the net radiation pattern(s) of the array.

Isn't a "non-radiating" feedline with a balun just an arbitrary length of
conductor, but now with a metallically conductive path to the driven
element(s), as well?

The feedline (and other metallic structures) adjacent to an FM broadcast
transmit antenna will affect the radiation patterns of the antenna even
though the measured match between the feedline and antenna input is
extremely good (even 1:1 SWR) -- in which case the line should have no
differential current to produce such an effect. What is the explanation for
that, please?

RF
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"Roy Lewallen" wrote in message
...
The radiated field in which a feedline is immersed produces a common
mode, not differential, current on the feedline(*). ETC