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

Maritime-Mobile Satellite Propagation Effects 9-21
unchanged for swell conditions. The multipath fading due to swell gives greater
contributions by as much as 4 dB, 2 dB, and 1 dB (for the different combinations of gain
and elevation angle) vis-à-vis the wind-wave contribution.
9.5.2 Dependence on Frequency
The analysis by Karasawa et al. [1990] alluded to above enable a computation of the
relation between frequency, significant wave height and fading depth. A set of fade
isopleths at the 99% probability exceedance level were calculated by them and have been
depicted in Figure 9-18 for an elevation angle of 5°, circular polarization, and antenna
gain of 15 dBi assuming wind-wave conditions [CCIR, 1990 (p.525-526)]. The left side
of the dashed line denotes the region where both coherent and incoherent multipath may
contribute whereas the right side of the dashed line is the region where the coherent
component is negligible.
In the region where incoherent multipath is dominant, (e.g., to the right of the dashed
line), the fading depth versus significant wave height decreases with increasing
significant wave height. This is evident in Figure 9-19, which represents a plot of fading
depth versus significant wave height at 10 GHz, 5 GHz, and 3 GHz extracted from the
curves of Figure 9-18.
Frequency (GHz)
10
9
1
8
7
6
5
4
3
2
6 dB
7 dB
7 dB
6 dB
5 dB
F d = 3 dB
4 dB
0.0 0.5 1.0 1.5 2.0 2.5 3.0
Significant Wave Height, H (m)
Figure 9-18: Calculation of contours of fading depth at the 99% probability exceedance
level for variable frequencies and significant wave heights assuming an elevation angle of
5°, circular polarization, antenna gain of 15 dBi, and wind-wave sea conditions are
assumed dominant. The region to the left of the dashed line corresponds to where the
coherent and incoherent components of multipath reflections may contribute.