Richard Fry wrote:
"The RADIATION performance of a transmit antenna should be considered
before anything else."

Yes. John D. Kraus, the inventor of the helical antenna, did just that.
In his 1950 edition of "Antennas" on page 176 Kraus wrote:
"The term "transmission mode" is used to describe the manner in which an
electromagnetic wave is propagated along an infinite helix as though the
helix constituted an infinite transmission line or wave guide. A variety
of different transmission modes is possible,

The term "radiation mode" is used to describe the general form of the
far-field pattern of a finite helix. Although an infinite variety of
patterns is possible, two kinds are of particular interest. One is the
axial or beam mode of radiation (R1 mode), and the other is the normal
mode of radiation (Ro mode).

Best regards, Richard Harrison, KB5WZI