472 AUTOMATIC TRACKING CIRCUITS 



and submit as much false information as possible to the measuring devices. 

 The accuracy of the measured data can be improved over the theoretical 

 minimum only by using more than one type of measuring device to obtain 

 signals from the same target. By correlating the different signals, the signal 

 strength can be enhanced without increasing noise in the same proportion. 

 The resulting improvement in the signal-to-noise ratio permits a more 

 accurate prediction of a target's position. Practically, such improvements 

 are limited by the complexity, reliability, weight, and cost of the added 

 equipment needed to obtain independent signals. 



The correlation techniques may have many different forms. Various 

 frequencies of radiation may be used to illuminate the target, not only in 

 the microwave range but in the infrared spectrum as well. Among the many 

 systems using a type of correlation technique are those with frequency 

 diversity, micropulses, "quickening," matched "frequency stretching" 

 filters, phase and amplitude comparators, and angle, range, and velocity 

 error comparators in pulsed doppler systems. 



The specific type of information needed for tracking a target depends on 

 several factors — the type of course being used in an attack on the target, 

 the relative position and motion between the target and the tracking 

 equipment, the amount of noise received, the weapons to be used against 

 the target, the type of course being flown by the target, and the type of 

 equipment used to obtain tracking information. Most of these factors are 

 different each time a target is being tracked; and theoretically, different 

 tracking information for computation and different tracking equipment 

 should be used for every attack condition in order to obtain the most 

 accurate information about the target. Of course it is impossible to have 

 an infinite variety of tracking equipment; but because the range of variation 

 in the optimization factors is not extremely large, it is possible to fabricate 

 a system with one or two modes of operation which will be nearly optimum 

 for the expected range of operating conditions. 



The basic information required for tracking is the position of the target 

 with respect to a space reference system as a function of time. In actuality 

 the target is usually some distance from the tracking device, moving with 

 respect to it, and consequently the position of the target may be described 

 by a vector which represents the range between the tracking device and the 

 target and is oriented along the space line of sight. Target information is 

 obtained by measuring characteristics of this vector. Frequently, it is only 

 the angular position of the vector that need be obtained, and in some cases, 

 only the angular rate of the vector in space need be known. Of course, 

 radar is a convenient means of obtaining this information because an 

 angular deviation between the radar beam and the target sight line, the 

 angular space error, can be obtained directly as an electrical signal; if this 

 signal is small, the measured antenna direction is almost identical with that 



