Leave length at 1 meter to get L' and C' in per meter units.

You can enter all radii as diameters instead, since ratios are taken.

Tube diameter can be smaller that array diameter, Ra and Rb are switched
in this case.

The first term in the equation for L' is exactly the impedance of coax
with Ra and Rb. So, you can think of the second term as the addition
inductance due to replacing one conductor with rods.

Sources:

Ron Boller who gives his
original source as "Russel".