PRF is pulse repetition frequency. PRF determination depends on maximum range at which target is expected to be detected. Echo signals received after PRF period is referred as multiple time around echoes. Figure depicts B and C signals in this category. These echoes cause erroneous calculation of radar range for the target referred as ambiguous range.
As shown in the figure, target A is within the maximum unambiguous radar range Runamb. Target B and C falls outside this. Range measured for target A is only correct while range measured for target B and C is ambiguous.
Unambiguous radar range is expressed as below:
Runamb = c/(2*PRF)
Where, c is the velocity of light 3 x 108 m/s
PRF is the pulse repetition frequency in Hz
Operating radar with varying PRF will help distinguish multiple timearound echoes from unambiguous echoes. This way, echo from unambiguous target (Here A) will appear at the same place while echoes from multiple time around echoes spread across the finite range as shown in the figure (Signal B and C).
Radar range resolution
Radar range resolution is the capability of the radar to distinguish or resolve nearby adjacent targets in the range. Search radars usually will have poor resolution and will distinguish two targets at about 100 meters apart.
The radar range resolution mainly depends upon following parameters/factors:
• transmitted pulse width
• type of target
• size of target
• radar receiver efficiency
• resolution of the radar display unit
Range resolution as a distance can be calculated as follows:
Rres = c * τ /2 Where, τ is the transmitted pulse width and c is the velocity of light in the free space.
Narrower beamwidth is very useful to distinguish two adjacent targets.