80 THE DEVELOPMENT OF WEAPONS SYSTEM REQUIREMENTS 



2-15 ACCURACY OF THE PROVISIONAL AEW SYSTEM 



For the hypothetical problem under consideration, there are 20 targets 

 and 40 interceptors — all of which could conceivably be in the zone of 

 coverage of a single AEW aircraft. Thus each AEW aircraft must be 

 capable of keeping track of 60 objects. Height measurements must be made 

 on a maximum of 20 objects (targets only). 



One facet of the accuracy problem — resolution — and its relation to 

 the overall system problem has already been discussed in Paragraph 2-13. 

 In addition to separating the 60 objects, the AEW/CIC system must also 

 track each object, i.e. determine its position relative to some reference 

 coordinate system and — for each of the attacking aircraft — its heading, 

 velocity, and altitude. As has been described, this information is utilized 

 to direct specific interceptors on collision courses with specific targets. The 

 required accuracy of this guidance depends upon the characteristics of the 

 interceptor system, particulary upon the AI radar and fire-control system. 

 The accuracy of the AEW/CIC system determines the accuracy with which 

 the interceptors can be vectored, and the vectoring error in turn determines 

 the required lock-on range of the AI radar. This last factor is a critical 

 item and may be severely limited by fixed elements of the problem and use 

 environment. Thus the AEW accuracy can only be firmly specified after 

 a study of the vectoring problem has determined the trade-off relation 

 between vectoring error and the required AI lock-on range.'' 



Unfortunately, because of the complex interrelations between AEW/CIC 

 system errors and vectoring errors, the analysis in Paragraphs 2-22 to 2-28 

 cannot be made abstractly but will require, as inputs, provisional assump- 

 tions of the AEW /CIC system design and accuracy. Thus, in this and some 

 of the following paragraphs, we shall assume tentative values for the required 

 AEW/CIC system accuracy and carry on our study of the preliminary 

 design of the AEW radar on the basis of these assumptions. We should 

 bear in mind, however, that these provisional values may lead to an un- 

 acceptable requirement for the AI lock-on range, in which case the analysis 

 would have to be repeated for a modified AEW/CIC system design. 



The AEW radar measures the relative position — azimuth and range — 

 of a target with respect to itself once per revolution of the fan beam. The 

 accuracy of each measurement, as it is seen in CIC, is limited by a number 

 of factors. The most significant of these are: 



1. Beamwidth 3. Data quantization 



2. Range aperture (pulse length) 4. Data stabilization 



5. Time delay errors 



''An illustrative analysis of this kind has been carried out in Paragraphs 4-6 and 4-7 of 

 Merrill, Greenberg, and Helmholz, of), cit. 



