question. (Bigger sizes of this imaginary sphere would produce stronger reflections.) Thus, RCS is an abstraction: the radar cross-sectional area of an object does not necessarily bear a direct relationship with the physical cross-sectional area of that object but depends upon other factors. Somewhat less informally, the RCS of a radar target is an effective area that intercepts the transmitted radar power and then scatters that power isotropically back to the radar receiver. More precisely, the RCS of a radar target is the hypothetical area required to intercept the transmitted power density at the target such that if the total intercepted power were re-radiated isotropically, the power density actually observed at the receiver is produced. This statement can be understood by examining the monostatic (radar transmitter and receiver co-located) radar equation one term at a time: where = transmitter's input power (watts) = gain of the radar transmit antenna (dimensionless) = distance from the radar to the target (meters) = radar cross-section of the target (meters squared) = effective area of the radar receiving antenna (meters squared) = power received back from the target by the radar (watts) The term in the radar equation represents the power density (watts per meter squared) that the radar transmitter produces at the target. This power density is intercepted by the target with radar cross-section , which has units of area (meters squared). Thus, the product has the dimensions of power (watts), and represents a hypothetical total power intercepted by the radar target. The second term represents isotropic spreading of this intercepted power from the target back to the radar receiver. Thus, the product represents the reflected power density at the radar receiver (again watts per meter squared). The receiver antenna then collects this power density with effective area , yielding the power received by the radar (watts) as given by the radar equation above. The scattering of incident radar power by a radar target is never isotropic (even for a spherical target), and the RCS is a hypothetical area. In this light, RCS can be viewed simply as a correction factor that makes the radar equation "work out right" for the experimentally observed ratio of . However, RCS is an extremely valuable concept because it is a property of the target alone and may be measured or calculated. Thus, RCS allows the performance of a radar system with a given target to be