130 



SITING AND COVERAGE OF GROUND RADARS 



Figure 25. Method of using the Cornu spiral. 



elements is odd the intensity is a maximum. That is 



(40) 



MP' - RP' = *j 



illuminated region may be determined by the follow- 

 ing analysis. The effect of the wave RM (Figure 29) 

 at P' may be considered to be due to the upper half 

 of the wave (above R), which is unaffected by the 

 edge, and the lower half of the wave (below fi), where n is an integer with values 1, 3, 5, etc., for 

 which is partly shielded by the edge. If RM contains 

 an even number of half-period elements the intensity 

 at P' is a minimum. If the number of half-period 



Figure 26. Relative power intensity— straight edge 

 diffraction. 



Figure 27. Relative electric intensity— straight edge 

 diffraction. 



