Many signal processing techniques used by modern radars take advantage of the differences in the Doppler frequency characteristics of targets, clutter, and noise to minimize the interference competing with the target signals, and thus to improve the probability of detection and the measurement accuracy. Consequently, it is useful to study the Doppler frequency characteristics of typical radar signals. The chapter begins by showing how the Doppler shift predicted by special relativity reduces to the very good standard approximation commonly used in radar, including in this book. The dependence on radial velocity is described. The principal focus of this chapter is on the Doppler spectrum of pulsed radar signals. The spectrum of the received signal for idealized stationary and moving point targets viewed with a finite pulse train waveform is developed step by step with key Fourier transform relationships introduced as required. These results are used to illustrate the concept of Doppler resolution. Attention then shifts to practical measurement of Doppler shift using finite pulse trains and Fourier analysis of the pulse-to-pulse phase shift. In doing so, the idea of coherent detection, first introduced in Chapter 1, is revisited. Finally, the contributions of noise, clutter, and moving targets are described to build an understanding of the range-Doppler or range-velocity distribution as viewed by stationary or moving (airborne or spaceborne) radars. The clutter foldover (ambiguity) effects on this distribution of range and velocity ambiguities are described and illustrated.

Chapter Contents:

• 8.1 Introduction
• 8.2 Doppler Shift
• 8.3 The Fourier Transform
• 8.4 Spectrum of a Pulsed Radar Signal
• 8.5 Why Multiple Pulses?
• 8.6 Pulsed Radar Data Acquisition
• 8.7 Doppler Signal Model
• 8.8 Range-Doppler Spectrum for a Stationary Radar
• 8.9 Range-Doppler Spectrum for a Moving Radar
• 8.10 Further Reading
• 8.11 References
• 8.12 Problems

Inspec keywords: Doppler shift; Fourier transforms; radar clutter; probability; airborne radar; interference suppression; Fourier analysis; radar signal processing; radar interference; data acquisition

Other keywords: radial velocity dependence; range-velocity distribution; pulsed radar signals; interference minimization; pulse-to-pulse phase shift; Doppler frequency characteristics; moving point targets; spaceborne radars; velocity ambiguity distribution; probability of detection; radar signal processing techniques; data acquisition; airborne radars; Doppler resolution; Doppler spectrum; Fourier analysis; finite pulse train waveform; Fourier transform; clutter foldover effects; radar clutter; Doppler shift measurement; target signals; Doppler phenomenology

Subjects: Electromagnetic compatibility and interference; Radar equipment, systems and applications; Other topics in statistics; Signal processing and detection; Integral transforms