The impedance looking into the feedpoint of an infinite dipole is
TWICE Zo.

Zo + Zo = 2*Zo.

The formula for Zo doesn't seem right. When the circumference of the
antenna rod is one wavelength, Zo = 0.

And when the circumference is greater than one wavelength, Zo becomes
negative.

For an 18 gauge wire, at a frequency of 183 GHz, something funny
happens.
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Reg.