2-18] 



AEW RADAR BEAMWIDTH AS DICTATED BY PROBLEM 



91 



effects are unknown. The details of this problem will be largely neglected 

 in the development of system requirements in this chapter. 



Vertical Beamwidth. Vertical beamwidth also is an important 

 factor. The AEW radar must detect and track the specified 50,000 ft 

 altitude targets. It should also have a capability for detecting and tracking 

 targets at all other reasonable values of altitude, since the specified threat 

 could not be considered realistic if there were significant holes in the early 

 warning coverage at other altitudes which could be exploited by the enemy. 



The characteristics of the threat determine the required vertical coverage. 

 If it is assumed that the primary threat (Mach 0.8, 50,000 ft) could also 

 attack from lower altitudes — for example, 10,000 to 50,000 ft — then, 

 AEW coverage must be provided over this range of altitudes. The coverage 

 must be sufficient that targets are not lost for appreciable periods of time. 

 For example. Fig. 2-25 shows that vertical coverage of 45° upward and 18.3° 



Altitude of 

 Primary Specified 

 ^Threat 



50,000 - 



Possible 

 Altitude Range 



of Targets 

 10,000 - 50,000 ft 



-10 -5n.mi. 5 10 



RANGE FROM AEW AIRCRAFT - n.mi. 



Fig. 2-25 AEW Vertical Coverage Diagram — Example. 



downward can create a zone 10 n.mi. in diameter where the primary target 

 (50,000 ft, 800 fps) can be lost from view. In the worst case, this would 

 involve loss of the 800-fps target for a period of slightly greater than 1 

 minute. With the assumed target spacing — 5 n.mi. — a maximum of two 

 targets would be within this zone at any one time. 



By the time targets enter this zone, the estimates of their velocity and 

 heading have been obtained quite accurately since they have been under 

 surveillance for almost 150 n.mi. These estimates may be used to update 

 the target position during the blind time, thereby reducing the effect of 

 the blind zone on system performance. Moreover, the tracking of objects 

 entering the zone is being done at very short ranges, and this greatly 

 improves the position accuracy of the data obtained just before the target 

 enters the zone. On these bases, it is reasonable to assume that dead zones 

 of the order of 10 n.mi. do not sensitively affect system performance, since 

 surveillance is lost for a relatively short time. Thus, vertical coverages 



