Digital Signal Processing Techniques and Applications in Radar Image Processing

4

FUNDAMENTALS OF RADAR

This chapter reviews basic theories of radar signal processing. Section 4.1 describes the principles of radar operation. Section 4.2 covers the basic configuration of a radar system. Section 4.3 and 4.4 discuss radar range equations, radar cross section, and clutter. Section 4.5 explains the Doppler frequency shifts from the wave propagation viewpoint. Radar resolution and ambiguity function are covered in Section 4.6.

4.1 PRINCIPLES OF RADAR OPERATION

By transmitting and receiving electromagnetic waves at regular time intervals, the radar is capable of identifying the distance from the target to the radar and/or the moving speed of the target. The detection and ranging functions can be accomplished either by timing the delay between transmission of a radio pulse and its subsequent return, or by calculating the difference in frequency between the transmitted signal and the echo signal. The pulse-based timing delay normally employs the amplitude modulation (AM) technique. Conversely, the frequency-difference-based ranging and detection method usually employs the linear frequency modulation scheme.

Consider the simple case of a radar system where a sequence of an AM pulse is transmitted. In this case, the information signal is a single pulse repeated at regular time intervals. The commonly used radar carrier-modulated pulse train is shown in Fig. 4.1.

In Fig. 4.1, the pulse repetition interval (PRI) is represented as T, which is the time interval between the ...