Target based RCS
The RCS of a complex target, such as a ship or aircraft, depends on the look angle of the radar. As the geometry of the target’s scattering points changes aspect with motion, the target’s RCS varies, or scintillates. The same phenomenon takes place when the radar frequency changes because the relative position of the target scatterers, measured at different wavelengths, changes. Lastly, σ is polarization dependent. Given that we have no a prior knowledge of the shape and polarization properties of the target, the possession of a full polarization capability of a system ensures that maximum information of the scene containing targets and clutter is attained, σ is therefore time, frequency, polarization, and look-angle dependent.
Moving targets can be discriminated from some clutter because the returns from clutter have zero Doppler shift, and the RCS of a target scintillates whereas that of clutter remains constant.
For the purposes of calculating the range of a target, some designers assume that σ is the time-average RCS of the target at one polarization. Measurements of σ of complex targets at different polarizations and frequencies, as well as approaches to minimize it, form an established field of research.
As might be expected, the RCSs of combat aircraft as a function of look angle, polarization, and frequency are not available in the open literature. In the recent past, designers have accepted the figures of 1, 10, and 100 m2 for the RCSSs corresponding to cruise-type missiles, fighter planes, and bombers, respectively.