308 



GENERIC TYPES OF RADAR SYSTEMS AND TECHNIQUES 



Receiver 



+ n(t) 



Transmitter 

 u{t) 



Storage Device 



and 

 Variable Delay 



f^{f-T) = u{t-T) 



Multiplier 



Integrator 



2l j\(t) f2(t-r)dt 



■4>,Jr,T) 



Fig. 6-10 Simplified Cross-Correlation Detector. 



incomplete cross-correlation function. The problem of signal detectability 

 has been very exhaustively studied"* and reported in 1954 at the MIT 

 Symposium on Information Theory^. One conclusion is that for the case 

 of a known signal operating through white Gaussian noise, the cross- 

 correlation receiver is optimum. This result is based upon the likelihood 

 ratio criterion. 



Cross correlation has become very useful in extracting the doppler 

 frequency shift or range-rate information for moving targets, thus adding 

 a new method to aid in target detectability as well as in more accurate 

 tracking and multiple target resolution. In order to extract the doppler, 

 the incoming echoes must be processed so as to permit coherent integration®. 

 This is predetection integration, which in the case of a pulse-doppler system 

 means coherent video or IF integration. The cross-correlation principle is 

 embodied in all of the systems proposed for using range-rate information. 

 First, a coherent or stored noise-free reference must be available; then some 

 storage medium is required to permit integration; and finally some form of 

 very narrow-band doppler filtering must be employed. Fig. 6-11 shows a 

 block diagram of a straightforward or brute-force pulse-doppler system. 

 Here there are n range gates with m doppler filters per gate. It is readily 

 seen that a tremendous duplication of equipment is called for unless some 

 storage device can be placed in the system. 



*J. Neyman and E. S. Pearson, "On the Problems of the Most Efficient Tests of Statistical 

 Hypotheses," Phil. Trans. Roy. Soc. London A231, 289 (1933). 



1. L. Davis, "On Determining the Presence of Signals in Noise," Proc. Inst. Elec. Engrs. 

 London 99 (III), 45-51 (1952). 



E. Reich and P. Swerling, "The Detection of a Sine Wave in Gaussian Noise," J. Appl. Phys. 

 24, 289 (1953). 



R. C. Davis, "On the Detection of Sure Signals in Noise," J. Appl. Phys. 25, 76-82 (1954) 



W. W. Peterson and T. G. Birdsall, The Theory of Signal Detectability^ Electronic Defense 

 Group, University of Michigan, Technical Report No. 13, July 1953. 



^Transactions of the IRE, PGIT-4, September 1954. 



^Bernard D. Steinberg, Coherent Integration oj Doppler Echoes in Pulse Radar, Report 

 #182-112-1, General Atronics Corp, Aprif 1957. 



