2-15] 



ACCURACY OF THE PROVISIONAL AEW SYSTEM 



81 



Measurement Errors due to Beamwidth and Range Aperture. 



Referring to Fig. 2-21, if a large number of individual measurements were 

 made on a target at point T, the measured values could be plotted as prob- 

 ability density distributions of azimuth and range values about the point 

 T. For any single measurement, the indicated target position might lie 

 anywhere in the region encompassed by these distributions, e.g., the point 

 A indicated in the figure. 



T = Actual Position of Target 

 A= Measured Position of 



Target 

 t= Azimuth Measurement 



Error of AEW Radar 

 e„ = Range Measurement 



Error of AEW 

 a^= Standard Deviation of 



Azimuth Measurement 



Errors of AEW Radar 



0), = Standard Deviation of 

 Azimuth Measurement 

 Errors of AEW Radar 



R = Range from AEW to 

 Target T 



AEW Radar Location 

 Fig. 2-21 Representation of AEW Measurement Errors. 



It is convenient to describe the measurement errors by their standard 

 deviations or root mean square (rms) errors. The magnitudes of these rms 

 errors are closely related to the resolution capabilities previously dis- 

 cussed; however, the reader should be careful not to confuse the resolution 

 of two targets and the accuracy in tracking one. 



Accuracy describes the radar's ability to measure the position of a single 

 target; as a rough approximation the standard deviation of the errors of a 

 single measurement of target position may be considered to be about one- 

 quarter of the resolution capability. Actually, besides being related to the 

 beamwidth, the measurement error is a function of the signal-to-noise ratio 

 and the number of hits per beamwidth. An analysis of these relations is 

 given in Paragraph 5-1 1 . As an example, with a 5° azimuth beamwidth and 

 a pulse width of 12 Msec corresponding to 1 n.mi. (i.e. resolution capabilities 

 shown to be adequate in the preceding paragraph), the approximate ac- 

 curacy of a position measurement for a single scan will have rms values of 



(5)(0.25)(150) 



57.3 



3.3 n.mi. (at 150 n.mi. range) 



(7 A = 1-65 n.mi. (at 75 n.mi. range) 



(2-5) 



