For a center fed half wave dipole operated at resonance, the voltage and current at the feed point are in phase in time and there is zero reactance present in the impedance seen at the feed point.

For the points in between the center feed point and the ends of the antenna, are the voltage and current also in phase in time ? which would mean that everywhere on the antenna at resonance V and I are in phase and there is no reactance present anywhere ?

This is a different question to :

What is the impedance of an off-center fed resonant dipole?

Which asks how the feed point impedance changes as the feed point is moved away from the center.

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    $\begingroup$ How do you define "voltage at a point"? Voltage at the feedpoint is pretty obvious: it's the difference in electric potential between the two feedpoint terminals. But for a single point somewhere on the antenna, voltage is....? $\endgroup$ – Phil Frost - W8II Jun 25 '20 at 19:51

The short answer is yes, a theoretical, ideal, resonant dipole has no reactance. This statement break down at the ends of the dipole because there cannot be any current at and beyond the wire end.

In practice, a dipole has distributed resistance, capacitance and inductance due to material properties, physical dimensions and the environment (e.g. height above ground).

The link you provided actually does have the answer to your question if you study the graph carefully. I.e. reactance is close to zero up to approx 1/8 of a WL from the center. This can be used to T-match a dipole to a 300Ω or 450Ω balanced feed line.

Note that if you asymmetrically feed a 0.5 WL antenna (i.e. not in the center) then you no longer have a resonant dipole and on the longer section a phase reversal will occur.

More information: dipole feed matching and with a bit more theory: Practical Dipole/Monopole Geometries. Matching Techniques for Dipole/Monopole Feeds

  • $\begingroup$ Hello Manfred, and welcome to this site! Thanks for a great first answer. We look forward to seeing more of you here! $\endgroup$ – Mike Waters Jun 26 '20 at 1:35

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