In my dipole/vertical modeling and analyzer measurements, as frequency
is increased past quarter-wave resonance, I've noticed with interest
that both reactance and resistance peak at different times, as they
increase with frequency toward the half-wave point.

Resistance peaks at approximately the half-wave point as expected, but
inductive reactance always peaks a little earlier (lower frequency).
This is also indicated in the ARRL Antenna Book in Figures 3 through 5
on pages 2-3 and 2-4 (it's the bulging on the right side of each of
the curves).

For a given antenna of particular length, adding inductive or
capacitive reactance changes the magnitude of the reactance peak, but
not the frequency at which it occurs.

Changing the thickness of the radiating elements changes (lowers) the
frequency at which the reactance peak occurs, but it also changes
(lowers) the frequency at which resistance peaks, and the difference
in these two freqencies stays approximately the same.

Why does the reactance peak occur slightly earlier than
half-wavelength? Can it be mathmatically predicted/explained? Any help
would be appreciated.

Al, WA4GKQ