2-19] FACTORS AFFECTING HEIGHT-FINDING RADAR 93 



system logic, the height finder must operate with azimuth input commands 

 obtained from the AEW fan-beam radar. 



The possible dimensions of the height-finding radar are limited by the 

 dimensions of the AEW aircraft nose. For purposes of specification, it will 

 be assumed that the aircraft in the example may accommodate an antenna 

 with a maximum dimension of 3 ft. It is also assumed that such an antenna 

 may be gimbaled so as to be capable of performing the height-finding 

 function on objects within a ±80° horizontal zone around the AEW 

 aircraft's nose. The vertical coverage of the height finder must be matched 

 to the primary vertical pattern coverage of the fan-beam azimuth search 

 system. 



The assumed placement of the height-finder places a limitation on tactical 

 usage. To evaluate a target the AEW aircraft must be pointed within 

 ±80° of the line of sight to the object whose height is being measured. 

 Thus, by virtue of the assumed system logic, the AEW aircraft must 

 maneuver to perform its mission. The required maneuver must be within 

 the performance characteristics of the AEW aircraft. In addition, the 

 effect of the maneuver upon the stabilization problem must be evaluated. 



Requirements Dictated by Threat Evaluation. Height-finding 

 information need not be obtained at the same rate as position information 

 for the specified threat, since its altitude does not change during the attack. 

 In fact it need be measured only once during the specified attack. Once 

 again, the possibility of other attack situations must be considered. If the 

 enemy aircraft were capable of making an abrupt altitude change during 

 the attack, the height-finding system must be able to detect such a change 

 in time for appropriate defensive measures to be taken. 



Immediately following detection, the height-finding radar is required to 

 begin measuring target altitudes for purposes of raid evaluation. Ideally, 

 the evaluation of target altitudes should take place within the time allowed 

 for threat evaluation (assumed to be 3 minutes in the example). If we 

 allow an average time of 1 minute^" for the AEW aircraft turning to face 

 the raid, a total time of 2 minutes is available to measure target altitudes 



lOThe AEW aircraft speed is 200 knots. At this speed, and at a bank angle of 10°, the AEW 

 aircraft can turn at the rate of about l°/sec. 



where F = velocity in knots, </> = roll angle (degrees), andi/' = horizontal turning rate (°/sec). 

 Since the height-finding radar coverage is ±80° or 160°, the maximum turn required to bring 

 a target under height-finder surveillance is 100°. Thus, 100 seconds would be required in the 

 worst case for a 10° bank angle. On the average less than half this time would be required, 

 since the orientation of the AEW aircraft relative to the raid is random. Thus, the assumption 

 of 1 minute does not imply extreme maneuvers by the AEW aircraft. 



