Читать книгу Inverse Synthetic Aperture Radar Imaging With MATLAB Algorithms - Caner Ozdemir - Страница 56

Radar cross section (RCS) can be regarded as the measure of the EM energy intercepted and reradiated by an object (or target). The unit of RCS is square‐meters (m²). RCS is generally used to categorize the object's EM reflectivity or ability to scatter the EM energy for a particular direction and at a particular frequency.

RCS is the main parameter in detection of airplanes, ships, tanks, or, more commonly, military targets. The low observable (or stealth) aircrafts/ships are designed to give very low RCS values so that they cannot be detected by the opponent's radar. These special design features for low‐observable platforms include planar body surfaces that reflect the incoming wave to another direction and/or using special radar‐absorbing material (RAM)‐based coating or paint. Passenger airplanes, on the other hand, usually provide relatively much higher RCS values due to bare metallic surfaces that reflect almost all of the incoming energy, rounded shape design that scatters the EM wave almost in all directions, and canonical shapes and cavities (such as engine ducts) that scatter most of the incident EM wave in the backward direction. Furthermore, they are also big in size compared to fighters. Therefore, their RCS values are much higher than specially designed stealth aircrafts.

The concept of RCS plays an important role in radar imaging. In fact, monostatic ISAR images of a target are constructed by backscattered field measurements (or RCS measurements). If the backscattered RCS measurements from the target for different frequencies and different look angles are transformed back to where the scattering phenomena originate, what we basically obtained is nothing but the “ISAR image” of that target.