6-7] 



HIGH RESOLUTION RADAR SYSTEMS 



337 



First of all, the number of spectral lines contained in the transmitted 

 bandwidth determines the number of individual unambiguous pieces of 

 range information that the radar can collect from an angular volume 

 determined by the antenna beamwidth. Thus, as previously noted. 



A^. ^ ^ = -1. 



' fr Irr 



(6-52) 



Since each piece of range information represents a range interval of fr/l, 

 the total unambiguous range interval is simply 



Rn 



-'^'i-k 



(6-53) 



= Spectrum Broadening 

 Introduced by Scanning 

 and Target IVlodulation 



At this point it is worthwhile to recall the development of the matched 

 filter principle presented in Paragraph 5-10 and used as the basis for the 

 storage and correlation radar principles outlined in Paragraph 6-4. This 

 principle stated that the optimum 

 S IN ratio is obtained when the 

 detection filter transfer function is 

 the complex conjugate of the re- 

 ceived signal spectrum. Thus for 

 the pulse spectrum shown in Fig. 6- 



31, the optimum filter would have 

 the comblike appearance of Fig. 6- 



32, where the width of each tooth of 

 the comb is sufficient to pass the 

 modulations produced by targets 

 and scanning. The total effective 

 detection bandwidth of such a filter 

 may then be expressed 



r 



uu 



Fig. 6-32 



Optimum 

 Radar Spectrum 



—^Frequency 

 Filter for Pulse 



Be 



NrBi = B 



(6-54) 



Thus, obtainment of high range resolution with a narrow band receiving 

 system is theoretically possible; in fact, for a nonscanning radar operating 

 against nonfluctuating targets, the total required received bandpass 

 approaches zero. The application of the matched filter concept requires a 

 coherent system. 



These principles make it possible to conceive a wide variety of high- 

 resolution systems which circumvent the peak power and S jN ratio 

 limitations of noncoherent pulsed radar systems. In general, these systems 

 have the following common characteristics: 



1. A wide transmitted bandwidth {Bt = c jlRr,^ 

 minimum resolution element). 



where i?r.min = 



