Handbook of Propagation Effects for Vehicular and ... - Courses

9-8
Cθ = ( θo
− 7)
/ 2 dB for θo
< 7°
Propagation Effects for Vehicular and Personal Mobile Satellite Systems
(9-23)
Step 5: Find the mean power of sea reflected waves Pr (in dB) relative to the direct
power. This is given by
Pr r ij
= D + R + C (dB) (9-24)
θ
Step 6: Find the fading depth A (relative to the direct power) from Figure 9-1 by setting
the multipath power calculated from (9-24) to the abscissa. Least square fits of the
individual curves in Figure 9-1 follow the form
⎛ Pr
⎞
A = α exp ⎜−
⎟ (dB), (9-25)
⎝ β ⎠
where the parameters α , β in (9-25) are tabulated in Table 9-2 for different exceedance
percentages.
In Figure 9-3 through Figure 9-9 are given the fading depths versus the elevation angle
for antenna gains of 0, 5, 10, 15, 18, 20, and 25 dBi, respectively. These curves were
derived executing the above-described steps at 1.5 GHz, assuming circular polarization.
9.3.3 Example Calculation
Consider the following example:
f
G
θ
o
= 1.
5GHz
o
= 10 dB
= 6
o
Polarization
= Circular
(9-26)
It is desired to find the signal level variation (relative to the direct power) at the 99%
exceedance probability level. For circular aperture antennas, the half power beamwidth
BW in (9-15) is approximately given by
BW = ρ Go 180
/ 20 (deg), (9-27)
10
where ρ is the antenna efficiency factor (between 0 and 1). Assuming a nominal value
of 0.6 for ρ , BW ≈ 44°. Hence (9-15) is satisfied. We tacitly assume the conditions
(9-16) and (9-17) are also satisfied. Injecting G0 = 10 dB and θ r = 1. 5,
θo
= 9°
into (9-5),
we obtain Dr = -0.29 dB. Substituting θ o = 6°
into (9-23) results in Cθ = −0. 5 dB. The
reflection coefficient for circular polarization is given by RCC = -6.19 dB from Table 9-1
at θ o = 6°
. Substituting the above values into (9-24) gives the mean power of sea
reflected waves Pr = -6.98 dB. Finally, substituting α = − 24. 8271, β = −6.
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