8-2] 



EXTERNAL, INTERNAL NOISE INPUTS TO RADAR SYSTEM 



397 



may be taken as minimization of tracking noise, which may be categorized 

 as follows: 



Range tracking noise, with an rms value of art, is defined as the closed-loop 

 tracking variations of the measured target range relative to the range to a 

 fixed point on the target. Range tracking noise includes effects of the 

 complex nature of the target and receiver and range servo system noise. 

 Systematic range tracking errors arising from flight-path input information 

 are excluded from art. 



Angle tracking noise, with rms value of aat, is defined as the closed-loop 

 tracking variations of the measured target angular position relative to a 

 fixed point on the target. Angle tracking noise includes effects of the 

 complex nature of the target and receiver and angle servo noise. Systematic 

 angle tracking errors arising from flight-path input information are excluded 

 from aat. 



Range Tracking Noise. The general shape of the dispersion versus 

 range for the various noise factors entering into range tracking is shown in 

 Fig. 8-1. Since the various noise factors are uncorrelated, the total output 



10 100 



RELATIVE RANGE 



1000 



Fig. 8-1 Range Noise Dispersion Factors. 



noise amplitude (shown by the heavy line) representing range dispersion in 

 a given tracking system is found by summing the noise components in a 

 root-mean-square manner. To use the diagram of Fig. 8-1 for prediction of 

 system performance, at least one point on each characteristic must be 

 determined by measurements. In the case of external range noise, the 

 following facts are known: 



1. Fire-control radar range information contains noise resulting from the 

 finite size of practical targets. 



2. The total rms range noise, ar (in yards), may be predicted from a 

 knowledge of target size and shape. Measurements made with a split-video 

 error detector on a variety of single and multiple targets show an average 



