Radar System Engineering

SEC. 3.11] EXTENDED SC’RFACE 1’ARGETS 87
We can generalize this formula t o the case of an extended surface target,
if we replace a by an expression whose fmm will be deduced though
statistical arguments similar to those used in Sec. 3.10. As long as the
relative positions of the objects in the target layer are random,l we add
the power received from each object in the area to find the average
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L
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FIG.3.15.—Theareacontributingto the instantaneouspowerreceivedfrom an extended
surfacetargetis hmitedin rangeandazinluthhy theresolutionof theradarsystem.
level of the probability distribution. The average signal S will thus be
proportional to the area A, but it can also be expected to depend on
the aspect angle 8, in a way which need not be specified here beyond
l Specifically,we requirethat the wave trainsreceivedfrom the individual scattererswithinthe
targetareashouldcombine in randomphase,which will be the case
if the rangesI?i to the scatteringobjects are distributedwith a randomnessor deviation
much greaterthan one wavelength,over a rangeintervalAR itselfmuch greater
than one wavelength.