422 



REGULATORY CIRCUITS 



Thus, with an AGC loop gain of about 50 or 34 db, input variations of 

 100 db can be reduced to output variations of only ±1 db. 



8-17 



DYNAMIC REGULATION REQUIREMENTS OF AGC 

 LOOPS 



It was previously noted that amplitude noise fluctuations in the receiver 

 output will modulate steady-state lag errors in the angle tracking loop 

 output and can thus produce excessive angle tracking noise. For this reason 

 and also to minimize the possibility of saturation, the AGC loop should be 

 designed to remove most of the input amplitude fluctuations, particularly 

 those within the pass band of the angle tracking loop. Actually, if there 

 were no systematic errors, some slight improvement in the glint noise or 

 deviations in angle of arrival could be achieved with no AGC. The reason 

 for this is that there is a correlation between large deviations of the apparent 

 center of reflection of an aircraft target and deep amplitude fades, since both 

 effects are produced by destructive interference of the reflected signals. An 

 effective AGC will increase the receiver gain to compensate for fades and 

 thus increase the magnitude of the glint deviations. In a practical case, 

 this effect is more than balanced by the benefits of removing spurious 

 modulation from the error signal. 



Typical results from a simulator study of this problem are shown in 

 Fig. 8-18.^" In this case, the target noise spectrum (amplitude and angle) 

 had a width of 1 cps while the tracking servo had a similar bandwidth. The 



§;'■ 



1.6 



1.2 



0.8 



0.4 



Fig. 



3L 2L L L 2L 



LAG ERROR (Units of Target Span,/.) 



■18 Effect of AGC on Angle Tracking Noise as a Function of Servo Lag 

 Error. 



*"J. H. Dunn and D. D. Howard, "The Effects of Automatic Gain Control Performance on 

 the Tracking Accuracy of Monopulse Radar Systems," Proc. IRE 47, 430-435 (1959). 



