RADAR ANTENNAS 



305 



was driven by 115-volt, 60 cycle, single phase motor to which was coupled 

 a two-phase reference voltage generator. The motor rotated at approxi- 

 mately 1800 rpm which resulted in a scanning rate of 30 cycles per second. 

 This antenna was used with a 24-inch spun steel parabolic reflector which 

 provided, at the 3 db point, a beam width of approximately 11° and a beam 

 shift of 8.5° making a total beam width of approximately 20° when scan- 

 ning. The minor lobes were down more than 17 db (one way) from the 

 maximum; and the gain of this antenna was 21 db. This antenna assembly 



JUNCTION BOX 



'M 



PARABOLOIDAL 

 REFLECTOR 



Fig. 55— Mark 19 Ant^ 



was integral with a transmitter-receiver (Fig. 55) which was mounted on 

 the associated gun director. Consequently, the size of the reflector was 

 limited by requirements for unobstructed vision for the operators in the 

 director. As a matter of fact, for this type of radar system serious con- 

 sideration must be given to the size and weight of the antenna and asso- 

 ciated components. 



14.11 The Mark 28 Radar Antenna 



The beam from the antenna used in Radar Equipment Mark 19 was 

 relatively broad and to improve target resolution, the diameter of the 



