310 GENERIC TYPES OF RADAR SYSTEMS AND TECHNIQUES 



In order to effect an improvement in signal-to-noise ratio by predetection 

 integration, some technique must be used either to obtain signal coherence 

 at IF or video, or to ensure transmitted signal recognition for cross- 

 correlation purposes. The earliest methods employed coherent sources for 

 transmission or coherent local oscillators in reception. As the transmitted 

 signals became more complex and sophisticated, it was considered necessary 

 to use storage to retain an exact replica for cross-correlation purposes. 

 Both electrostatic storage and magnetic-tape storage have been developed 

 and used successfully. The limited dynamic range of electrostatic storage 

 combined with relatively short storage times, and the relatively slow 

 accessibility of the data on magnetic tape have created an interest in 

 magnetic-drum storage. As advanced technical progress provides increased 

 dynamic range and higher frequency operation, the tremendous data 

 handling capacity combined with high-speed record and readout and long- 

 duration storage make magnetic-drum storage appear very desirable for 

 radar use. 



Fig. 6-13 shows a system using transmitted-waveform storage to provide 

 a reference for the cross correlation and magnetic-drum storage to reduce 



TR 



Transmitter 



Storage & 

 Range Gate 





Receiver 



Multiplier 



Magnetic Drum Doppler 



Storage Output 



Fig. 6-13 Storage Radar. 



the equipment multiplication required in Fig. 6-11. The transmitted- 

 waveform storage unit could be envisioned to consist of multiple delays 

 corresponding to the n range gates of Fig. 6-11. There could be a separate 

 track on the magnetic drum corresponding to each value of delay — i.e., to 

 each range gate. For a given channel or track on the magnetic drum, the 

 return echo pulses could be clipped and converted essentially to a binary 

 code, which could then be painted sequentially so as to form the doppler 

 signal as a modulation on the code.'' The doppler frequency could be 

 explored as before by a doppler filter bank as shown. Only an elementary 



