Radar Cross Section (RCS) - MATLAB Simulations for Radar Systems Design - page 497

when θ s = θ i and ϕ s =

θ s

ϕ i , defines the monostatic RCS. The RCS measured

by the radar at angles ≠ θ i and ϕ s ≠ ϕ i is called the bistatic RCS.

The total target scattered RCS is given by

2π
∫

π
∫

1
4π

------

σ t = σθ s ϕ s ( , ) sin θ s d θ d ϕ s

(11.5)

ϕ s = 0 θ s = 0

The amount of backscattered waves from a target is proportional to the ratio
of the target extent (size) to the wavelength, , of the incident waves. In fact, a
radar will not be able to detect targets much smaller than its operating wave-
length. For example, if weather radars use L-band frequency, rain drops
become nearly invisible to the radar since they are much smaller than the
wavelength. RCS measurements in the frequency region, where the target
extent and the wavelength are comparable, are referred to as the Rayleigh
region. Alternatively, the frequency region where the target extent is much
larger than the radar operating wavelength is referred to as the optical region.
In practice, the majority of radar applications fall within the optical region.

λ

The analysis presented in this topic mainly assumes far field monostatic
RCS measurements in the optical region. Near field RCS, bistatic RCS, and
RCS measurements in the Rayleigh region will not be considered since their
treatment falls beyond this topic Ós intended scope. Additionally, RCS treatment
in this chapter is mainly concerned with Narrow Band (NB) cases. In other
words, the extent of the target under consideration falls within a single range
bin of the radar. Wide Band (WB) RCS measurements will be briefly addressed
in a later section. Wide band radar range bins are small (typically 10 - 50 cm);
hence, the target under consideration may cover many range bins. The RCS
value in an individual range bin corresponds to the portion of the target falling
within that bin.

11.2. RCS Prediction Methods

Before presenting the different RCS calculation methods, it is important to
understand the significance of RCS prediction. Most radar systems use RCS as
a means of discrimination. Therefore, accurate prediction of target RCS is crit-
ical in order to design and develop robust discrimination algorithms. Addition-
ally, measuring and identifying the scattering centers (sources) for a given
target aid in developing RCS reduction techniques. Another reason of lesser
importance is that RCS calculations require broad and extensive technical
knowledge; thus, many scientists and scholars find the subject challenging and
intellectually motivating. Two categories of RCS prediction methods are avail-
able: exact and approximate.