Cecil Moo
So the coil-loaded, short radiator is not really "electrically" ~90
degrees long -- it just has the reactance of an antenna that is
~90 degrees long. (R. Fry quote)

But Richard, that is what is meant by "electrical" length, that it has
the same phase shift as a ~90 degree antenna.
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So the definition of electrical length you use excludes radiation
resistance? That resistance is the only parameter giving any antenna the
ability produce useful EM radiation in a practical antenna system. And that
resistance is a function of the physical properties and configuration of the
radiator with respect to the operating frequency.

Model a short vertical radiator in NEC, and check its impedance. If short
enough, it could be something like 0.1 -j2500 ohms. Now add an inductive
reactance to the system to reach resonance. NEC then will show 0.1 +/-0
ohms. Note that the radiation resistance term did not change.

That short system is resonant, but it certainly won't have the practical
radiation efficiency of a full, 1/4-wave, linear radiator, even though they
both have the same "electrical length" by your definition.

RF