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BELL SYSTEM TECHNICAL JOURNAL 



in this country by the Signal Corps in the work described by General Colton, 

 to which reference has been made. 



The use of two antenna beam (or lobe) positions to obtain more accurate 

 radar angle data is referred to as lobe swilching and the operating principle 

 is illustrated in Fig. 25. The antenna beam is shown in two positions: 

 position 1 being directed to the right, and position 2 to the left of the me- 

 chanical axis of the antenna. The antenna beam is caused to switch rapidly 

 between these two positions, and simultaneous with this switching a small 

 horizontal displacement of the indicator Class A sweep is introduced. In 



Fig. 21— Radar Mark 3 antenna on Destroyer Porter (Navy Photo 2711-42) 



this manner the signals received in the two beam positions may be viewed 

 separately. The speed of switching is made sufficiently high to minimize 

 flicker and the efifect of fading signals. It will be noted from this diagram 

 that the signal strength received from target A is the same for both beam 

 positions thereby producing equal "pip" heights on the indicator screen. 

 However, for target B the signal amplitude is greater in position 1 than in 

 position 2 and the "pip" amplitudes on the indicator differ correspondingly. 

 If the operator wishes to track target B it is only necessary for him to 

 rotate the antenna until the two "pips" are of equal amplitude. Smooth 



