Читать книгу Inverse Synthetic Aperture Radar Imaging With MATLAB Algorithms - Caner Ozdemir - Страница 73

As calculated in Eq. 2.58. the range resolution is proportional to the pulse duration as Δr = c·τ/2. Therefore, the smaller the pulse duration, the finer the range resolution we can get. On the other hand, maximum range is determined by time delay between the transmitted and received pulses. Since the pulses are repeated for every T_PR seconds, any received pulse that is reflected back from a target at R distant on the range should arrive before the next pulse is transmitted to avoid the ambiguity in the range, that is,

(2.63)

Figure 2.21 Pulsed radar systems use a sequence of modulated pulses.

If T_PR is fixed, then the range should be less than the following quantity:

(2.64)

Therefore, the maximum range that can be unambiguously detected by the pulsed radar is calculated by the period between the pulses, that is, T_PR, as given below:

(2.65)

This is also called unambiguous range since any target within this range is accurately detected by the radar at its true location. However, any target beyond this range will be dislocated in the range as the radar can only display the R_max modulus of the target's location along the range axis. To resolve the range ambiguity problem, some radars use multiple PRFs while transmitting the pulses (Mahafza 2005).