Ian wrote:
"Are there any calculations or charts for centre impedance of a dipole
in free space, starting from zero length, and going out to infinity?"

It gets repetitive after a while.

Arnold B. Bailey has "Graph of the resistance of a center-fed antenna
near first resonance and below" on page 343 in "TV and Other Receiving
Antennas". Then on page 348 Bailey has: "Various orders of resonance of
thin center-fed antennas, showing the current loops and approximate
radiation and antenna resistance in each case.".

Best regards, Richard Harrison, KB5WZI