Inverse Synthetic Aperture Radar Imaging With MATLAB Algorithms. Caner Ozdemir

Inverse Synthetic Aperture Radar Imaging With MATLAB Algorithms - Caner Ozdemir


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It is clearly seen from this figure that chirp signal provides much wider bandwidth when compared to constant‐frequency pulse.

      In radar applications, LFM pulse waveforms are mainly utilized in finding range profiles, and also for synthetic aperture radar (SAR) and ISAR processing as will be discussed in Chapters 3 and 6, respectively.

      2.7.1 Pulse Repetition Frequency

      2.7.2 Maximum Range and Range Ambiguity

      (2.63)equation

Schematic illustration of radar systems use a sequence of modulated pulses.

      (2.64)equation

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

      (2.65)equation

      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 Rmax 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).

      2.7.3 Doppler Frequency

      In radar theory, the concept of Doppler frequency describes the shift in the center frequency of an incident EM wave due to movement of radar with respect to target. The basic concept of Doppler shift in frequency has been conceptually demonstrated through Figure 2.10 and is defined as

      (2.66)equation

      (2.67)equation

      Looking at the situation in Figure 2.22b, it is obvious that the pulse distance before the reflection is equal to the distance traveled by the leading (or trailing) edge of the pulse plus the distance traveled by the target as

      (2.68)equation

      Similarly, the pulse distance after the reflection is equal to the distance traveled by the leading (or trailing) edge of the pulse minus the distance traveled by the target as

      (2.69)equation

      Dividing


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