6 ELEMENTS OF AIRBORNE RADAR SYSTEMS DESIGN PROBLEM 



The foregoing discussion of the search, detection, and identification func- 

 tions points out an important characteristic that affects the performance 

 of these functions. This characteristic is the implied uncertainty that 

 the desired result will be obtained in a given case. The element of uncer- 

 tainty requires a statistical approach to the problem of understanding 

 and analyzing the detection and identification characteristics of a radar 

 system. 



Tracking. A radar system may be designed with the capability of 

 measuring the relative range, range rate, and bearing of any object which 

 scatters microwave energy impinging on it. When a radar makes any or 

 all of these measurements on a more or less continuous basis (depending 

 upon whether it is also searching), it is said to be tracking the target. The 

 tracking function can provide information for: 



1. A continuous display or record of relative target position as a 

 function of time 



2. Calculation of relative target motion 



3. Prediction oi future relative target position 



The range measurement is achieved by measuring the elapsed time 

 between a transmitted signal and the reception of the portion of the 

 transmitted energy that is scattered by the target back along the direction 

 of transmission and multiplying it by a constant representative of the 

 average propagation velocity. The radar energy is propagated at the 

 speed of light {c = 328 yd/jusec). Thus the time required for the radar 

 energy to travel from the transmitter to the target and back to the trans- 

 mitter location is 



. = ?^. (M) 



c 



The range to the target may be expressed 



R = '^= I64t yards (1-2) 



where R = range to target in yards 



/ = time in microseconds between transmission and reception 



c — propagation velocity in yards per microsecond. 



The closing velocity along a line from the radar to the target (range rate) 

 can be measured by means of the frequency difference between the trans- 

 mitted and received signals caused by the relative target motion. This 

 doppler effect will be discussed in Paragraph 1-5. 



