96 THE DEVELOPMENT OF WEAPONS SYSTEM REQUIREMENTS 



not be appreciably larger than that of the fan beam or it will have difficulty 

 resolving between adjacent targets that are resolved by the fan beam. 

 Thus, as a first approximation, the azimuth beamwidths of the height 

 finder and the fan-beam radar may be made approximately equal. 



The elevation beamwidth depends upon the required accuracy. An 

 approximation may be obtained by using the same expression employed for 

 fan-beam azimuth accuracy (Paragraph 2-15). 



Cn = 6n/4 degrees (rms) for a single measurement (2-24) 



an = Qnl'^yln degrees (rms) for n measurements (2-25) 



where n = number of measurements averaged to obtain a single estimate 



9n = elevation beamwidth of height-finding radar. 



Since 6 seconds can be taken for the height-finding measurement, it is 

 reasonable to assume that five to ten separate measurements could be made. 

 If, e.g., nine measurements are made, the required beamwidth is found by a 

 manipulation of the above equation as 



e„ = 4V^ c7„ = (4) (3) (0.27) = 3.2°. (2-26) 



Actually, techniques known as beam splitting can be employed to obtain 

 greater angular accuracy than is implied by Equation 2-26. Accordingly, 

 the derived result is only one of the possible solutions to the height-finding 

 problem. 



2-20 SUMMARY OF AEW SYSTEM REQUIREMENTS 



The preceding discussions have shown some major considerations 

 involved in the design of a typical AEW system. Numerical examples 

 illustrated the various interrelations and were chosen in such a manner as 

 to be applicable to the solution of the hypothetical air defense problem we 

 have been considering. 



We may now use all of this information to compile an estimate of the 

 basic characteristics of an AEW system which represents a reasonable 

 answer to the overall system problem. These estimated characteristics may 

 then be employed to provide the basic input data needed to specify the AI 

 radar and fire-control system. All during this process, we estimate — as 

 best we can — the overall system performance to ensure that we do not 

 depart from the mission accomplishment objectives. As already mentioned, 

 in an actual overall systems study, we would repeat this process several 

 times to obtain a better feeling for the trade-offs between the AEW system 

 and the AI system. However, for all cases, the basic considerations and 

 the method of attack on the problem would remain very much the same; 

 only the assumed system logic and specific parameter values would undergo 

 appreciable change. 



