FIRE-CONTROL R.\DARS FOR NAVAL VESSELS 



23 



stabilization in elevation to take care of pitch and roll of the ship. Such 

 stabilization was not required with the broad elevation beam obtained with 

 the 3 ft. by 12 ft. antenna; and in addition, this wider antenna provided 

 more accurate tracking due to the narrower antenna beam in azimuth. 

 Installations of these antennas aboard ship arc shown in Figs. 20 and 21 

 and 22, 23 and 24. 



Fig. 20 — Radar Mark 3 antenna (6' x 6') on Cruiser Honolulu (Navy Photo 144-6-42) 



Antenna Lobe Switching 



The problem of measuring angles accurately with a relatively broad 

 radio beam has been faced many times in the radio direction finding art. 

 The most successful attack has made use of the fact that while the nose of a 

 radio antenna beam is blunt, the sides of the beam are relatively steep; i.e., 

 while the rate of change of signal amplitude with angle is very low near the 

 nose of the beam it becomes substantial down on the side of the beam. 

 A very well known application of this principle is the airway radio range 

 wherein two very broad overlapping beams define a narrow path by uti- 

 lizing the points where the two overlap with equal intensity. A somewhat 

 similar scheme in which the antenna beam is switched rapidly between 

 two positions has been applied in radar, and in an early form was first used 



