antenna-theory.com

[Externet]

What is radiation resistance of an antenna and how is it calculated ?

[helix]

Radiation resistance is concept used when representing an antenna as an equivalent circuit. It accounts for the power that the antenna transmits to free space. As far as the circuit is concerned, the radiated power is gone from the circuit, so a resistor is appropriate (a resistor dissipates, or removes, power from a circuit). You can find general formulas for radiation resistance in any intro antenna text, e.g. Stutzman and Thiele.

[Externet]

Thanks, helix.

Is the formula
Rr = 1580 * ( He / wavelength)^2
valid ?

Rr = radiation resistance,
He = effective height, expressed in fractions of a wavelength, of the distributed common-mode current

[helix]

That formula is probably only valid for electrically short dipoles/monopoles. I'd suggest following the derivation of the formula (wherever you got it from) to ensure that the assumptions going into the derivation are valid for your particular case.