498 AUTOMATIC TRACKING CIRCUITS 



antennas and in different systems. No specific design or design method can 

 be given concisely, but the basic design principles discussed in this chapter 

 must be considered when determining the angle track characteristics for 

 any system. 



9-10 INTRODUCTION TO RANGE AND VELOCITY 

 TRACKING 



The subject of radar range tracking is first mentioned in this book in 

 Paragraph 1-4 preceding the radar range equation, Equation 1-2. The 

 concepts of indirect determination of range rate by differentiation of radar 

 range information and of direct measurement by doppler frequency shift, 

 Equations 1-19 and 1-20, are introduced in subsequent paragraphs. Dop- 

 pler frequency is again discussed in Paragraph 4-4, in connection with sea 

 return in Paragraph 4-11, and in connection with cross-correlation radar 

 in Paragraph 6-4. Paragraph 6-6 is entirely devoted to concepts related to 

 pulsed doppler radar systems. This last paragraph discussed a method of 

 range tracking wherein the entire interpulse period was covered by contigu- 

 ous fixed-range gates. Each range gate interval was divided into contiguous 

 velocity (doppler frequency) intervals (see Fig. 6-11). In such systems range 

 and velocity tracking is provided by a radar data processing system (or com- 

 puter) which records the channel location of each signal return. The AEW 

 system discussed in Chapter 2 is an example of a system that might employ 

 such tracking areas. 



In single target systems such as the x'\I radar of Chapter 2 or a missile 

 target seeker, the range and velocity tracking problem is somewhat 

 different. Generally these systems have only a single channel for the flow 

 of target information. Range and velocity tracking is accomplished by 

 time and frequency gates which are controlled to bracket the received pulse 

 and doppler frequency of the target return (See Paragraph G-5 for an 

 example of a moving velocity gate). 



The following paragraphs will discuss the basic principles of range and 

 velocity tracking as they are commonly applied to single target systems. 

 The principal emphasis will be given to the dynamic problems of automatic 

 systems designed for such purposes, since the electronic problems of gating 

 circuits and time and frequency discriminators have been adequately 

 covered in the general literature. 



9-11 AUTOMATIC RANGE TRACKING 



The principal functions of the range tracking unit may be listed as 

 follows : 



1. To provide means for automatic measurement of target range 



