Pre detection integrator the resultant or integrated

pre detection integrator, the resultant, or integrated, signal-to-noise (power)
ratio would be exactly n times that of a single pulse. If the same n pulses
were integrated by an ideal post detection device, the resultant signal-to-
noise ratio would be less than n times that of a single pulse. This loss in
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Radar Systems Lecture Notes J.Sridevi Assoc.Prof. Unit 1:Basics of Radar and Range Equation
integration efficiency is caused by the nonlinear action of the second
detector, which converts some of the signal energy to noise energy in the
rectification process.
The integration efficiency may be defined as follows:
6. Write short notes on radar cross section of targets.
Radar Cross Section of Targets:
The radar cross section of a target is the (fictional) area intercepting that
amount of power which when scattered equally in all directions, produces an
echo at the radar equal to that from the target; or in other terms,
This equation is equivalent to the radar range equation. For most common
types of radar targets such as aircraft, ships, and terrain, the radar cross
section does not
necessarily bear a simple relationship to the physical area, except that the
larger the target size, the larger the cross section is likely to be.
Scattering and diffraction are variations of the same
physical process. When an object scatters an electromagnetic wave, the
scattered field is defined as the difference between the total field in the
presence of the object and the field that would exist if the object were absent
(but with the sources unchanged). On the other hand, the diffracted field is
the total field in the presence of the object. With radar backscatter, the two
fields are the same, and one may talk about scattering and diffraction
interchangeably.
The radar cross section of a simple sphere is shown in Fig. as a
function of its circumference measured in wavelengths (2Πa /λ, where a is the
radius of the sphere and λ is the wavelength). The region where the size of
the sphere is small compared with the wavelength (2Πa/λ << 1) is called the
Rayleigh region.
The Rayleigh scattering region is of interest to the radar
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Radar Systems Lecture Notes J.Sridevi Assoc.Prof. Unit 1:Basics of Radar and Range Equation
engineer because the cross sections of raindrops and other meteorological
particles fall within this region at the usual radar frequencies. Since the cross
section of objects within the Rayleigh region varies as λ
-4
, rain and clouds are
essentially invisible to radars which operate at relatively long wavelengths
(low frequencies). The usual radar targets are much larger than raindrops or
cloud particles, and lowering the radar frequency to the point where rain or
cloud echoes are negligibly small will not seriously reduce the cross section
of the larger desired targets.
Fig. Radar cross section of the sphere. a = radius; λ = wavelength
At the other extreme from the Rayleigh region is the optical region , where
the
dimensions of the sphere are large compared with the wavelength (2Πa/λ