90 THE DEVELOPMENT OF WEAPONS SYSTEM REQUIREMENTS 



The selected value of 5° was representative of a likely allowable upper 

 limit for the AEW radar design on the basis of resolution. The use of larger 

 beamwidths would complicate the problem of target resolution since the 

 angular beamwidth would then be appreciably larger than the angular 

 separation of the targets (Fig. 2-20) at the maximum vectoring range 

 (75 n.mi.). 



Since the system accuracy is almost a direct linear function of beamwidth, 

 the estimated accuracy of the provisional AEW design represents the 

 poorest that might be obtained from a potentially suitable AEW design. 

 Thus the accuracy performance characteristics of the provisional AEW 

 design will tend to place the most severe requirements on the interceptor 

 system. If the interceptor system can be built to meet these requirements, 

 the same interceptor system will be more than adequate for smaller values 

 of AEW radar beamwidth. On the other hand, if the selected value of 5° 

 makes AI radar requirements unreasonable, the maximum permissible 

 AEW radar beamwidth may have to be reduced. The objection to a 

 reduced beamwidth is the larger antenna which it entails and the penalty 

 thus imposed upon the AEW aircraft. 



In this chapter, only the interrelationships of AEW radar beamwidth 

 with the tactical problem are discussed. As will be seen in Chapter 3, radar 

 beamwidth also enjoys close interrelationships with other parameters and 

 performance characteristics of the radar system. Among these are (1) 

 detection range, (2) information rate, (3) operating frequency, (4) antenna 

 size, and (5) stabilization requirements. 



In addition, AEW radar beamwidth affects the response of the radar 

 system to electromagnetic disturbances arising in the tactical operating 

 environment. Enemy countermeasures, radar returns from clouds and 

 ground, and radiations from other AEW aircraft are representative of such 

 phenomena. Strictly speaking, the consideration of these factors should 

 be made at the same time as the resolution and accuracy requirements 

 studies since they are an important part of the AEW radar's relationship 

 with the overall tactical problem. For simplicity, the discussion of these 

 factors is deferred until Chapter 14 because a knowledge of radar techniques 

 and propagation phenomena is necessary to make such a discussion mean- 

 ingful. 



To summarize, then, AEW radar fan beamwidth is dictated by three 

 primary tactical considerations: resolution, vectoring accuracy, and inter- 

 action with electromagnetic disturbances. Resolution considerations have 

 been shown to dictate a value of about 5° or less. Vectoring accuracy 

 requirements are unknown at the present time. In order to proceed with 

 the problem, the vectoring accuracy obtainable with a 5° beam will be used. 

 Subsequent analysis of the AEW and AI systems will disclose whether 

 vectoring accuracy dictates a narrower beam. Electromagnetic disturbance 



