The physical arrangement of the elements is different, of course, but otherwise the only difference is the addition of the equivalent gain of the target RCS factor. RCS area is not the same as physical area. While it's understood that RCS is the antenna aperture area equivalent to an isotropically radiated target return signal, the target gain factor represents a gain, as shown in the equivalent circuit of Figure 1. The radar illustrated in Figure 1 is monostatic so the two path losses are the same and the values of the two 's are the same. Because the factors are given in dB form, they are more convenient to use and allow calculation without a calculator when the factors are read from a chart or nomograph.
Most radars are monostatic.
That is, the radar transmitting and receiving antennas are literally the same antenna. Figure 2 is the visualization of the path losses occurring with the two-way radar equation. Losses due to antenna polarization and atmospheric absorption also need to be included. The Radar Range Equation is simply the Radar Equation rewritten to solve for maximum Range. It occurs when the received echo signal just equals S min .