= Monostatic radar equation
{title2=$P_R=P_TG^2\lambda^2\sigma_{\rm back}/[(4\pi)^3D^4]$}
For a far-field free-space link with one reciprocal <antenna> transmitting and receiving at range $D$, the outward intensity is $P_TG/(4\pi D^2)$. The backward scattered intensity at the receiver is this times $\sigma_{\rm back}/(4\pi D^2)$. Multiplying by the matched <antenna effective area> $G\lambda^2/(4\pi)$ gives the displayed received <power>. Attenuation, misalignment and polarization mismatch require additional factors. The threshold for a <root mean square> voltage $V_m$ across a real matched load $R$ is $V_m^2/R$.
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