D. G. Tucker 45 
DELAY 
LINE 
FEEDBACK 
NETWORK 
O OUTPUT 
INPUT 
DELAY 
LINE 
FEEDBACK 
NETWORK 
Fig. 2.15. Double-loop signal integrator system. 
a hypothetical (ideal) system in which the best weighting is given to every com- 
ponent signal at all times. 
a. Uniform weighting of the optimum number of signal returns, the system 
input being cut off before and after these returns—0.5 db worse than the 
ideal system 
b. Single-loop continuous integrator with optimum loop gain—0.95 db worse 
than the ideal system 
c. The new double-loop integrator with optimum loop gains—0.3 db worse 
than the ideal system 
In view of the fact that the double-loop integrator is thoroughly practical, 
its performance is so close to the ideal that its use seems well justified. It is 
somewhat surprising, however, that the investigation shows the form of the 
integrator to be so uncritical. What we do not know at present is how far the 
performance of ordinary P.P.I. displays (where there is some integration on 
the phosphor) falls below the performance of these properly designed integration 
systems. 
2.4.2, Pattern Recognition and Size of Target 
It has been mentioned previously that the detectability of a signal in noise is 
improved by causing the signal to trace out a line on successive returns, as in 
the chemical recorder. It would be expected that, correspondingly, a signal pat - 
tern of any shape would show increasing detectability as its area increased re- 
lative to the "grain" of the noise background. Probably, the shape itself would 
have some influence on detectability. 
Recent experimental work by Nagaraja [22] at Birmingham, using a cathode- 
ray display, has shown that: 
a. Circular patches show a decrease in threshold of detection of about 2.3 db 
per doubling of area, provided the area is fairly small (<100 min? as 
