THE RADAR RECEIVER 



783 



derived by integration of the sweep wave form as impressed upon the ele- 

 ments i?2, C2 and the voltage appearing across C2 is effectively superimposed 

 upon the output wave form. As employed on an airborne bombing radar 

 equipment, a circuit similar to that shown in Fig. 51, was employed where a 

 residual nonlinearity of less than 0.5% was achieved and maintained under 

 severe military operating conditions. 



In certain instances it is desirable to generate a sweep wave form which 

 has a specific nonlinear time characteristic. An illustration of one such 

 case as applied to airborne radar is given in Fig. 52. Here the airborne 

 radar display was required to present a nondistorted ground plan which in 



^y-^' 



GROUND RANGE, GR=VS^-H^ 



Fig. 52.— Development of hyperbolic sweep wave form for true ground plan radar 

 presentation. 



turn required that the range sweep wave form be of a hyperbolic form. The 

 start of the display sweep must be delayed in time corresponding to the time 

 of propagation and return of the radar pulse between the aircraft and the 

 ground. This delay may be produced by the use of a multivibrator of a 

 convenient form, actuated by a pulse coincident with the outgoing radar 

 pulse, and where the duration of the multivibrator pulse is controlled either 

 manually or automatically by reference to the aircraft's altimeter. 



The hyperbolic sweep wave form illustrated may be approximated mathe- 

 matically as the sum of a linear and a series of exponential terms. In this 

 particular application, it was found sufficient to consider a linear and two 

 additional exponential terms only to satisfy these specific requirements. 

 Figure 53 indicates the method employed to generate this specific wave 

 form. As indicated, the desired theoretical hyperbolic sweep function has 



