2-11] AEW SYSTEM LOGIC AND FIXED ELEMENTS 71 



Initial detection of the target is provided by the fan-beam radar. This 

 equipment also measures slant range to the target, R, and target azimuth 

 position 6 with respect to a reference direction. 



The height-finding radar is positioned in azimuth with information 

 obtained from the fan-beam radar. It measures the elevation angle of the 

 target y with respect to the horizontal. The sine of the target elevation 

 angle, multiplied by the range R and modified by AEW aircraft altitude 

 and an earth curvature correction, provides a measure of target altitude h. 

 The measured target data are displayed in the AEW aircraft for monitoring 

 purposes. 



The AEW system encodes the measured range, azimuth, and height 

 information and transmits this intelligence to the CIC in the form of a 

 digital message. AEW aircraft position — as obtained from the navigation 

 system — is also transmitted via the digital communications link. 



The task force is provided with means for ascertaining AEW aircraft 

 position relative to the combat information center (CIC) but with an error 

 dependent upon the specific defense problem. A standard deviation of 1 

 n.mi. in both the rectangular coordinates is assumed for our analysis, as 

 defined in Fig. 2-3. 



Several AEW aircraft are employed — the number and disposition will 

 be derived in the succeeding paragraph. The information from all AEW 

 aircraft is presented on a master tactical display in CIC to permit overall 

 battle control and surveillance. 



Each AEW aircraft measures range and azimuth of all aircraft within its 

 zone of surveillance. Height measurements are made only on the designated 

 targets; the interceptors are commanded to climb to target altitude, so there 

 is no reason (in this example) for measuring the interceptor altitude. 



CIC System Information Processing. The polar coordinate (R, 6) 

 information gathered by the AEW radars is transformed into a common 

 rectangular (cartesian) coordinate system by the CIC computer to facilitate 

 the generation of target heading and velocity information. Rectangular 

 coordinates have an advantage over polar coordinates because constant- 

 velocity, straight-line flight paths can be represented by x and y velocity 

 components which also remain constant. Thus, if the position, P(/), of a 

 constant velocity straight-line target at any time t is designated in rec- 

 tangular coordinates, then 



m-lox-{-joy (2-1) 



where ^, jy = target position in rectangular coordinates at time ( 



to, jo = unity vectors along the Xo and jo axes of the stationary 

 rectangular coordinate system. 



