760 BELL SYSTEM TECHNICAL JOURNAL 



has proven quite satisfactory. Similar presentation methods developed 

 for airborne aircraft interception rachir equijjments have employed, in 

 addition, separate instruments to notify the i)ilot or gunner at the time when 

 the range to the target was proper for firing of the guns. Another variation 

 in method of obtaining accurate range information simultaneous with the 

 elevation and azimuth data is through the employment of automatic range 

 tracking. In this case after identihcation and selection of the target has 

 been made and the initial coincidence accomplished, the operator is then free 

 to track in elevation and azimuth with the automatic tracking device con- 

 tinuing to furnish the changing range data to the gun. 



Figure 37 indicates the fact that included in these display forms are varia- 

 tions which are a function of the deflection coordinates peculiar to the display 

 device itself. The factors which determine this choice are related to the 

 required form of the presentation from the standpoint of military use, the 

 characteristics of the particular display device available and the mechanical 

 form of the antenna scanning system. 



It should be observed that a number of minor variations in the exact 

 presentation is available to the radar system designer within the general 

 classification indicated in Fig. 37. As mentioned previously, the A-type 

 display may be modified to indicate azimuthal pointing errors. In this case, 

 sometimes referred to as a K-type display, the radar system employs an 

 antenna capable of producing two beams of radiation, available one at a 

 time, with azimuthal bearings diiTering by the order of the beam width. 

 Two signals, each of which is associated with one position of the radiated 

 beam, are displayed in the basic A-type form with one slightly displaced in 

 the range coordinate with respect to the other. By "steering" the antenna 

 until the amplitude response of the desired target appears equal for each 

 image, the target bearing is determined as the direction line bisecting the 

 two antenna lobes. 



It is often desirable to limit the display to a small area or to a small se- 

 lected range interval to enable magnification of this particular portion of the 

 scene. The accurate measurement of range for fire-control purposes can 

 be accomplished on a conveniently small indicator screen by expanding only 

 a selected small range inter\al of interest. The loss of information at other 

 ranges under these conditions is unimportant. In certain airborne apjili- 

 cations it is desirable to present large area information for navigational 

 purposes, but at the time of starting the radar bombing attack the area of 

 interest is limited to a narrow sector extending outward from the plane in 

 the direction of the attack. Here a selected sector may be expanded with a 

 ])r<)bable increase in accuracy of indixidual largi't identification and final 

 bombing accuracy. 



In the "range only" classification of I'ig. 37 the J-typc of display has an 



