RADIO PROPAGATION FUNDAMENTALS 



007 



as H approaches (grazing incidence), and that it increases with in- 

 creasing positive vahies of H. When the direct ray clears the obstruction, 

 // is negative, and the shadow loss approaches db in an oscillatory 

 manner as the clearance is increased. In other words, a substantial clear- 

 ance is required over line-of-sight paths in order to obtain "free-space" 

 transmission. The knife edge diffraction calculation is substantially 

 independent of polarization as long as the distance from the edge is more 

 than a few wavelengths. 



cl,^d, 



ANT 

 2 



\ 



-50 



-30 

 -20 

 \ 



l-io 



\ 



h5\l 



5000- 



2000- 

 1000- 



^ 500- 



til 

 LU 

 u- 200 • 



-3 

 -2 





* 



100- 

 50- 



20- 

 10- 



- 10,000 



- 5000 



3000 

 -2000 



-1000 



- 500 



*-^^ 



-0.5 



-0.3 

 -0.2 



-0.1 



\ 



30 \ 

 -20 ^ 



10 



|- 5 



3 



- 2 



- 1 



■^ note: 



when accuracy greater than 

 ± 1.5 db is required, values on 

 the d, scale should be: 



30- 

 60- 



150- 

 300- 

 600 



1500H 

 3000 7 

 6 000- 



1 5,000 - 

 .36,000- 



O 

 z 

 o 

 u 



LU 



a. 



UJ 

 Q. 



CO 



LU 



_l 



u 

 e) 



LU 



2 



U. 



o 



LU 



_l 

 < 

 > 



111 

 > 



I- 

 < 



UJ 



I/) 





0- 



UJ 



z^ iH 



/ 



g-0.8 



- 



•10 I 



1-12 



7\A 



-16 

 -18 

 -20 



O 

 a. 



2b en 



_i 



LU 



m 



■30 \l, 

 a 



z 

 ■35 ^ 



O 



-40 



-45 



- 50 



d2 



Fig. 7 — Knife-edge diffraction loss relative to free space. 



