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

Maritime-Mobile Satellite Propagation Effects 9-7
3
o
BW
≤θ o ≤ . (9-15)
4
• The sea condition is such that the roughness parameter u defined as:
is given by
4π
u = h sin( θo
)
( -16
λ
2 ≤ u 10,
(9-17)
where λ is the wavelength in m, θ o is the elevation angle to the satellite, h0 is the RMS
wave height in m related to the significant wave height H by
ho = H 4 . (9-18)
Employing Figure 9-2, (9-17) implies for instance, at 5° elevation
1. 5 H 7.
3 or 0.
4 ho
1.
8 ( m)
≤ ≤
≤ ≤ . (9-19)
Step 2: Find the relative antenna gain Dr (in dB) in the direction of the specular reflection
point on the sea. The relative antenna gain is approximately given by
D r
−4
Go
/ 10 2
( ) r
= − 4 × 10 10 −1
θ , (9-20)
where G0 is the antenna gain in dBi (dB above isotropic), and
θ = 15 . θ
(9-21)
r o
when the beam center is in the direction of the satellite. The factor of 1.5 (as opposed to
2) is used since a significant portion of the multipath energy comes from the region
between the true specular reflection point and the horizon [Karasawa and Shiokawa,
1984a].
Step 3: Obtain the Fresnel reflection coefficient Rij (in dB), where i represents the
polarization of the incident wave and j is the polarization of the reflected wave. These
reflection coefficients are tabulated for the sea at 1.5 GHz in Table 9-1 for horizontal
polarization RHH, vertical polarization RVV, and circular polarization RCC. The Fresnel
reflection coefficients may also be calculated using the formulas of Beckmann and
Spizzichino [1963].
Step 4: Calculate the correction factor C θ in dB given by
and
Cθ = 0 dB for θo
≥ 7°
(9-22)