Range ambiguity Pulse repetition frequency

a real target in 100 km or second-sweep echo in distance of 400 km?

a radar system determines range through time delay between pulse transmission , reception relation:

range

=



c
τ

2




{\displaystyle {\text{range}}={\frac {c\tau }{2}}}

for accurate range determination pulse must transmitted , reflected before next pulse transmitted. gives rise maximum unambiguous range limit:

max range

=



c

τ

prt



2


=


c

2


prf







{




τ

prt


=


1
prf










{\displaystyle {\text{max range}}={\frac {c\tau _{\text{prt}}}{2}}={\frac {c}{2\,{\text{prf}}}}\qquad {\begin{cases}\tau _{\text{prt}}={\frac {1}{\text{prf}}}\end{cases}}}

the maximum range defines range ambiguity detected targets. because of periodic nature of pulsed radar systems, impossible radar system determine difference between targets separated integer multiples of maximum range using single prf. more sophisticated radar systems avoid problem through use of multiple prfs either simultaneously on different frequencies or on single frequency changing prt.

the range ambiguity resolution process used identify true range when prf above limit.