SITING AND COVERAGE OF GROUND RADARS 
The product of f; and f, is the modified antenna fac- 
tor f(y). This is plotted in Figure 64. With a larger 
reflecting surface, the length of lobes would approach 
twice the value of f,. Figures 64 and 65 were drawn 
for purposes of illustration and would not ordinarily 
be required. 
Example 18. Cliff Edge Diffraction. A 200-me radar, 
Figure 66, with an antenna as described in Example 
h, «50 FEET 
CLIFF EDGE = 3000 FEET 
f=200 Mc 
£(S) =z fF, 
= 
wu MODIFIED ANTENNA 
! 400 PATTERN FOR SEA 
z LOBES 
= 
i 200 
x 
° 
x 0 ty 
FREE SPACE 
OUGH PATTERN OF 
LAND rete ANTENNA 
SURFACE OF SEA 
te) 4000 8000 
12000 
DISTANCE d, IN FEET 
Ficure 66. Cliff edge diffraction. (Example 18.) 
16, is 50 ft above a rough land surface, the top of a 
cliff whose edge is 3,000 ft away. 
The geometrical shadow line makes an angle with 
the horizontal of 
50 
ye OU eee 5 
tan ( Ait) 0.955° . 
At this angle, the relative intensity, z = 0.5. Other 
values of z may be read from Figure 27 after con- 
verting the angle of diffraction to » by means of 
equation (47). 
(3) 
if) 
B 
ANTENNA [gi ey Yq 
6 c__T, ne) Se 
—— 
= v y-20 
U 
Wy 
| 37, __to tarcet 
Cc —1 
a 9 ee 
G 8 
u 
ig 
h! 
\ 
pe 2,0 
qT 
IMAGE 
f (3) 
117 
1 = — = 0:61 6;° . 
Vian ens 
At 0.377° in the shadow region v = —0.377 X 0.61 
= —0.23. From Figure 27, z is 0.4. This angle, 
referred to the horizontal at the antenna, is 
y = & — 0.955 = —1.332°. 
Some other values are: 
fe Zz 
+3.535 0.917 
+1.060 1.18 
—0.955 0.50 
—8.335 0.05 
The modified antenna pattern f(y) is the product 
of z and f, and is plotted in Figure 66. This pattern 
gives the factors for both the direct and reflected 
waves for the sea lobes. 
Example 19. Land Reflection and Diffraction. This 
site is similar to that of Example 18 except that the 
cliff top is smooth. This is shown in Figure 67. 
\ ANTENNA f=200 MC 
SMOOTH LAND 
600 FT 3000FT 
5000 FT 
t 
Figure 67. Land reflection and diffraction. (Example 
19.) 
DIRECT RAY 
CENTER LINE OF 
ANTENNA PATTERN 
H 
E 
REFLECTED 
y) x-78 
vzt-e-) [2— Hee y 
) D 
H CENTER: LINE OF 
ANTENNA PATTERN 
Ficure 68. Earth curvature effect on direct and image patterns. Note: GH horizontal at the antenna; CE horizontal at 
, dy 
the reflect: i = = 
e reflection point @ Pe 
