RADAR ANTENNAS 



287 



weather protection, in a housing which can transmit 10 cm radiation. 

 \'isible also is the waveguide run down the mast to the r.f. unit. 



The SL radar provides a simple non-stabiUzed PPI (Plan Position 

 Indicator) display. The antenna is driven by a synchronous motor at 

 18 rpm. Horizontal polarization is used to minimize sea clutter. The 



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Fitr. 4U — SE Antenna. 



radiating structure, shown in Figure 42, consists of a 20" sector of a 42" 

 paraboloid. The resulting larger beam width in the vertical plane is pro- 

 vided in order to improve the stability of the pattern under conditions of 

 ship roll. Figure 43 illustrates the path of the transmitted wave from the 

 SL r.f. unit to the antenna. It also illustrates the manner in which horizon- 

 tally polarized radiation is obtained. The diagram shows the position of 



