The energy intercepted by the target will be:

                                                                                                                                (1)

where s is the back scattering cross section of the target. NOTE: s is not necessarily equal to the geometrical cross section.

The amount of energy which gets back to the antenna is:

                                                                                                                            (2)

The amount of power that is collected by the antenna is:

 								(3)

where [P_r] = watts

A_e = effective area of the antenna

What are typical values of these quantities?

P_t ~ 10⁵ W

r ~ 100 km

G ~ 40 dB

s ~ 1 m²

Inserting these numbers into the above equation gives

The gain can be express in terms of the effective area of the antenna and the wavelength of the radar by:

  or							(4)

so substituting (4) into (3) gives:

   This is the radar equation for a point target.