112 THE DEVELOPMENT OF WEAPONS SYSTEM REQUIREMENTS 



Look- Angle Requirements. If lock-on is to occur at any selected 

 range in the 8-30 n.mi. interval, the radar must be able to "look" at the 

 target. That is to say, the maximum look-angle of the AI radar antenna 

 must be sufficient to encompass the distributions of probable target angular 

 positions relative to the interceptor heading. {Look-angle is often referred to 

 as gimbal angle or train angle). 



A typical situation is shown by Fig. 2-33. The possible positions of the 

 target relative to the interceptor are shown as a distribution of angular 

 positions around the lead angle Ld that would exist for perfect vectoring. 



Note: Lq- Collision Course 

 Lead Angle 

 tg=Lead Angle Limit 



Total Area Under 

 



LOOK ANGLE, I 



Fig. 2-33 Probability Density Distribution of Target Angular Positions Relative 

 to Interceptor Heading. 



For any range and angle off the nose, such a figure could be formulated from 

 the data in Figs. 2-28 and 2-32 in the preceding paragraph. The probability 

 that the AI radar can look at the target at this range and angle is simply 

 the area under the curve that lies between the AI radar look angle limits Lg. 

 The look-angles required to ensure that 95 per cent of the targets are 

 within the AI radar field of view are displayed in Fig. 2-34. The prices of 

 short-range lock-ons and "around the clock" attack capability are evi- 

 denced by the large radar gimbal angles required to maintain 95 per cent 

 probability. When the lock-on range satisfying the conversion probability 

 requirement is found, Fig. 2-34 may be used to determine the AI radar 

 gimbal angle dictated by vectoring considerations. 



Display Requirements. From Fig. 2-29, we see that the vectoring 

 system transmits required attack altitude, time to collision, and range 

 relative to the interceptor — in addition to the heading commands already 

 discussed — to provide tactical situation information to the pilot. All the 

 vectoring information plus pitch and roll information must be presented on 



