304 



GENERIC TYPES OF RADAR SYSTEMS AND TECHNIQUES 



in the orthogonal video deflection circuits. Such an indicator has been 

 called a "Pisa indicator" after the famous leaning tower. 



To accomplish the operation described it is convenient to generate 

 the overlapping antenna patterns with a single aperture. This may be 

 accomplished with a single parabolic reflector illuminated by two primary 

 radiators symmetrically displaced laterally from the focus. 



The principle has been described for a single angle coordinate. Extension 

 to two angle coordinates is not ordinarily accomplished by duplicating the 

 system, but the one-coordinate system may be modified to operate as a 

 two-coordinate system. It is first necessary to generate four lobes in the 

 antenna pattern. This is accomplished by using a cluster of four primary 

 radiators symmetrically disposed about the focus, with two up, two down, 

 two right, and two left. Sum and diff^erence signals are obtained separately 

 from two pairs. The two difference signals are then added to generate error 

 signals in one coordinate. Sum and difference signals are then obtained 

 from the two first sums. The resulting diflFerence signal is used to generate 

 error signals in the other coordinate. The second or final sum signal, which 

 is the sum of all four lobes, carries target amplitude and range information 

 and provides a common phase reference for both coordinate error signals. 

 The angle information may be utilized in a wide variety of configurations. 

 Shown in Fig. 6-8 is one of the most common: an automatic angle tracking 

 system such as might be employed in an AI radar or guided missile terminal 

 seeker. 



L 



Antenna 



F<M 



Azimuth 



Diff. 

 Channel 



Elevation 



n 



Diff. Channel 

 Sum Channel 



Antenna 

 Controller 



^ I 



Jg Automatic Angle ^ 



Y^ Tracking Loop M 



Azimuth 

 Amp. 



Phase 

 Det. 



Error 



Elevation 

 Amp. 



Phase 

 Det. 



Sum 

 Amp. 



Range 



Fig. 6-8 Two-Coordinate Monopulse System. 



