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

Summary of Recommendations 12-15
12.9 Maritime-Mobile Satellite Propagation Effects (Chapter 9)
This chapter deals with multipath fading from the ocean when low gain antennas are
employed at low elevation angles for ship-satellite scenarios. The results apply
predominantly at L-Band.
12.9.1 Fading Depth Due to Sea Surface Reflections
Below is a summary of steps adopted by the ITU-R for evaluating the fading depth due to
sea surface reflections:
Step 1: Confirm the applicable parameters for which the method is valid. These are:
Frequency range from 1 to 2 GHz (nominal frequency is 1.5 GHz).
Polarization circular or horizontal. Vertical polarization may be used for elevation angles
above 8°. Below 8°, noticeable errors may exist for vertical polarization due to Brewster
angle complications.
Elevation angle θ o is within the interval
3
o
BW
≤θ o ≤ . (12-17)
4
The sea condition is such that the roughness parameter u is defined as
u = hoSin o
4π
( θ ) , (12-18)
λ
where u has the range
2 ≤ u ≤ 10
(12-19)
and where λ is the wavelength in m, θ o is the elevation angle to the satellite, h o is the
RMS wave height in m related to the significant wave height H by
H = 4 ho . (12-20)
Equation (12-20) implies
15 . ≤ H ≤ 7. 3, 0. 4 ≤ ho ≤ 18 . ( m)
. (12-21)
Step 2: Find the relative antenna gain D r (in dB) in the direction of the specular
reflection point of the sea. The relative antenna gain is approximately given by
D r
−4
Go
/ 10 2
( ) r
= − 4 × 10 10 −1
θ , (12-22)
where G o is the antenna gain in dB (dB above isotropic), and