6-4] 



CORRELATION AND STORAGE RADAR TECHNIQUES 



309 



w 



TR M — Transmitter — ► Delay 



Receiver 



Multiplier 



Coherent 



Video 





Fig. 6-11 Pulsed-Doppler System. 



Storage Radar. We have noted that one of the first and perhaps 

 simplest of all storage mechanisms consisted of a visual observer using an 

 A scope. Next, in the PPI, screen persistence performs the storage, and 

 scan-to-scan integration is attained. Finally, the last form of postdetection 

 integration to become significant was of the video type. Here the storage 

 element could vary from a video delay line to some form of electrostatic 

 storage. A simple delay-line video integrator is illustrated in Fig. 6-12. 



Fig. 6-12 Simplified Delay-Line Video Integrator. 



The number of pulses which can be effectively integrated to improve the 

 signal-to-noise ratio depends upon the delay line loss, feedback circuit stabil- 

 ity, distortion, and the length of time the target remains essentially at a fixed 

 range. Video integration of pulses embedded in additive Gaussian noise 

 at the radar input improves the signal-to-noise power ratio by the 

 number of pulses added; the total improvement possible after detection, 

 then, is limited by the observation or integration time permissible. 

 From Fig. 6-9 it is seen that there is a detector loss for any detector 

 input below threshold (S /N= 1) and that the ultimate radar sensitivity 

 is obtained by predetection rather than video integration. 



