150 



SITING AND COVERAGE OF GROUND RADARS 



in the region of greatest interest, that is, small 

 angles, hi is itself small, and this tends to compen- 

 sate the error. The modifications introduced permit 

 the use of the simple plane earth formulas, since for 

 a particular angle the tangent plane is taken as the 

 reflection surface. 



The angle y given by equation (62) is the trans- 

 formed angle to be used in constructing the vertical 

 coverage diagram based on a modified earth radius 

 of ka = 5,280 miles. If the true angle is desired, the 

 true earth radius a = 3,960 miles must be used in 

 equation (62) instead of 5,280 miles. 



Examples 11 and 12. Lobe Angles Corrected for 

 Earth Curvature. Lobe angles will be computed by 

 this method for two radar sites. 



Example 11 



Kr = 500 ft 

 / = 200 mc 



From equation (59) 



hi' = 500 - ^ 



Example 12 



hi = 3,000 ft 

 f = 100 mc 



hi' = 3,000 - — 



<? 250 



20 30 40 50 60 70 



DISTANCE dj IN MILES 



Figure 50. Equivalent height graph. 



Table 6. Lobe angles for radar. (Example 11.) 



