= Radiation resistance
{title2=$P_{\rm rad}=I_{\rm rms}^2R_{\rm rad}$}
{wiki}
<Radiation resistance> represents emitted electromagnetic <power> as a real input resistance of an <antenna>. It does not describe conversion to heat inside the conductor. If peak current amplitude is used, $P_{\rm rad}=|I_0|^2R_{\rm rad}/2$. Real ohmic loss adds a separate resistance and lowers radiation efficiency. For an ideal short uniform-current element of length $d$, the <Hertzian dipole> gives $R_{\rm rad}=80\pi^2(d/\lambda)^2$ in ohms, using the usual vacuum impedance approximation $120\pi\,\Omega$.
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