RMax = ( ( Pt *G* S * Ae ) / ( ( 4 * PI)2 * PMin))
Where PMin = Minimum Detectable Signal of Receiver, S = Radar Cross Section Area, Ae = Antenna Aperture, G = Maximum Power Gain of Antenna, Pt = Transmitted Pulse Peak Power, RMax = Radar Range.
For example, when Pt = 2, G =3, Ae = 4, S = 5, PMin = 6, Then Radar Range is 0.126779669612181.