Practical_Antenna_Handbook_0071639586

C h a p t e r 2 : r a d i o - W a v e P r o p a g a t i o n 35
where N 1 = refractivity at 1 km altitude
h r = height of receive antenna
h t = height of transmit antenna
C e = L n (N s /N 1 )
N a = refractivity at altitude
N s = refractivity at earth’s surface
For models close to the surface, use the geometry shown in Fig. 2.16A, where distance
d is a curved path along the surface of the earth. But because the earth’s radius r o
is about 4000 statute miles and thus very much larger than any practical antenna height
h, the simplified model of Fig. 2.16B can be used. The underlying assumption, of course,
Earth's surface
h
d
r o
r o r o 4000 mi
Figure 2.16A Geometry for calculating radio line-of-sight distances.
h
d
Figure 2.16B Simplified geometry.