474 AUTOMATIC TRACKING CIRCUITS 



optimum relationship between the tracking bias errors caused by the 

 moving target and the random errors caused by inherent fluctuations in 

 the radar error signal. A bandwidth too narrow would produce large bias 

 errors in real time with small random errors, and a bandwidth too wide 

 would produce small bias error with large random error components. The 

 basic problem of tracking loop design is to find the optimum compromise 

 between these conflicting considerations. 



The automatic range and angle tracking loops must be endowed with 

 memory during short intervals when the radar signal fades and target 

 information is not available. This is usually done with relatively simple 

 networks which provide an approximation to an integral. 



Another significant problem which arises in tracking control systems is 

 that of cross coupling between control channels, particularly in the angle 

 track loops. Cross coupling exists in basic space geometry when vector 

 rates are translated into various reference frames in the antenna, in the 

 platform, or in the weapon coordinate systems. There are other sources of 

 coupling between channels — improper separation of the radar error signal 

 into the proper antenna gimbal coordinate, incorrect choice and orientation 

 of rate-measuring gyros, poor mechanical design in which motion in one 

 channel is induced by motion in another, and high impedance in common 

 power supplies, which may be electrical or hydraulic. 



Details of these space-vector tracking problems are discussed in the 

 following paragraphs. 



9-2 AUTOMATIC ANGLE TRACKING 



The primary function of the angle tracking system is to derive the 

 direction and angular rate of the line-of-sight with an accuracy needed for 

 an adequate solution of the fire-control problem. As discussed in Paragraph 

 8-23, space stabilization must be provided during the tracking operation. 



The angular direction to the target is determined basically by an auto- 

 matic control system which directs the radar beam toward the target. The 

 error between the antenna boresight and the target sight line is detected as 

 a modulated signal. This signal, proportional to the angular space error, 

 is amplified and applied to actuators which drive the antenna to reduce the 

 angular space error. The direction and magnitude of the motion that the 

 servo motor must provide to correct the error is usually obtained as a d-c 

 signal by demodulating the tracking error signal derived by the radar. 



As described in Paragraphs 8-23 and 8-29, angular space stabilization is 

 provided by gyros, usually mounted on the antenna, and by the radar 

 tracking loop itself. 



