6-2] BASIC PRINCIPLES 299 



angles, and velocity. For such a system the information rate may be 

 expressed (from Equations 6-1, 6-2, 6-9, and 6-12): 



iV = TV, X A^c X TVa X A^. = ^ X/s X N,. (6-15) 



The minimum detection bandwidth/^ that could be employed with such a 

 system is of the order of the bandwidth induced by scanning /^ as previously 

 mentioned. Thus the number of parallel channels needed to process all the 

 radar data in minimum time is 



N//d = N/fs ^ ^ X N, = Nr X N,, number of channels. (6-16) 



This development shows that such a radar would require a separate 

 channel for each range resolution element for a total of Nr range channels; 

 each range channel would possess, in turn, 7V„ velocity channels. A repre- 

 sentation of such a system is shown in Fig. 6-11. 



The only means for reducing the number of channels required is to 

 increase the detection bandwidth or to increase the total scanning time and 

 employ time-sharing of the receiving channels. A noncoherent pulse radar 

 is a good example of the first approach: in this case the predetection 

 bandwidth is made equal to (or greater than) Aft and only one channel 

 is needed. 



A CW radar with a sweeping velocity gate is a good example of the 

 second approach; in this case, the various velocity intervals are examined 

 sequentially. This permits single-channel operation at the cost of increasing 

 the total interrogation time by a factor equal to the number of velocity 

 intervals, as will be explained in Paragraph 6-5. 



A number of means — other than the brute force approach indicated — 

 exist for creating parallel information channels. Principal among these are 

 the storage techniques described in Paragraph 6-6 and the delay-line 

 filtering techniques described in Chapter 5. 



The filtering techniques commonly employed in radar receivers may be 

 listed as follows: (1) mixing, (2) bandpass filtering, (3) gating, (4) demodu- 

 lation, (5) clamping, (6) cross-correlation error detection, (7) comb filtering, 

 and (8) video integration. Chapter 5 developed the basic mathematical 

 theory of these techniques with illustrations taken from the example of a 

 pulse radar system employing conical scan angle tracking. The basic 

 principles developed for each of these operations do not change; thus the 

 material developed in Chapter 5 provides a means for tracing and analyzing 

 the flow of signal plus noise through any radar receiver. The generic 

 systems discussed in subsequent paragraphs will provide examples of the 

 various filtering and receiver sampling techniques as they are used in other 

 types of systems. 



