See pg 8-7 through 8-23 of Phys. Des. of Yagi Antennas. Note that this is
the formula for the characteristic impedance, not the input impedance, of
the element. This is used to get the reactance variation around resonance.
For a tapered element, you can substitute into the formula
Zo = 60 * (ln (2*h/a) -1) an equivalent radius ae such that
ln(ae) = SUM OF Ln ln(an/h), where Ln is the length of each section of
radius an. This is most easily done by setting up a spreadsheet, with
columns for each section of the element and rows for section radius,
section length, and Ln ln(an/h), which when summed across gives ln(ae).
Then Zo = 60 * (ln (2*h/ae) -1)
Dave, W6NL (ex-QHS)
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