RA1 TRACING 



45 



0©O(°) 



Figure 3. Rays with a ground-based duct. 



© © © Q® * 



-»- DISTANCE x 



Figure 4. Rays with an elevated duct. 



basis it is necessary to know the phases associated 

 with the rays so as to determine their mutual inter- 

 ference. If this is done by an appropriate graphical 

 or numerical method, contours of constant field 

 strength can be drawn. Figure 5 shows, typical cov- 

 erage diagrams computed in this way, 146 correspond- 

 ing to a value of hi/\ = 20. The lines separating 

 the "detection zones" from the "blind zones" indi- 

 cate ranges at which a medium bomber would just 

 become visible to the particular radar to which these 

 diagrams apply. Diagram 1 shows the undistorted 

 lobe diagram for standard refraction while dia- 

 grams 2, 3, 4, 5 show the coverage diagram for 



various types of ground-based and elevated ducts. 



In Figure 6 is shown the variation of field strength 

 with height for various distances for the M curve 

 shown on the left-hand side of the figure. 73 The 

 transmitter is at a height of 60 m. 



In all diagrams shown in this section the vertical 

 scale is vastly exaggerated as compared to the 

 horizontal scale. It may readily be shown that when 

 the representation is such that the earth is curved, 

 the contours of constant height can be represented 

 by parabolas in the approximation where the true 

 vertical elevations are small compared to the hori- 

 zontal distances involved. 



