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

Maritime-Mobile Satellite Propagation Effects 9-23
were greater than –6 dB, -4 dB, and –3 dB, respectively for the case when h = 0.91 m.
There results showed that the fading depth peaked at h = 0.4 m and diminished slightly at
greater wave-heights.
9.6.2 Extension of the Kirchhoff Classical Model
Sobieski and Guissard [1993] extended the Kirchhoff classical approach for mobile
maritime satellite propagation using the boundary perturbation method (BPM) [Brown,
1980; Guissard and Sobieski, 1987]. They evaluated carrier to specular and carrier to
multipath ratios and compared these results with those derived by measurements and by
other models. Comparing their calculations with results from other measurement
campaigns, they obtained generally good agreement.
9.6.3 K/Ka-Band Maritime Experiments
Perrins and Rice [1997] describe shipboard measurements employing the Advanced
Communication Technology Satellite (ACTS) Mobile Terminal (AMT) [Abbe et al.,
1996]. The link was comprised of a ground terminal at the Jet Propulsion Laboratory in
Pasadena, California and the mobile terminal on board the USS Princeton in the eastern
Pacific Ocean (October 1996), where the ACTS steerable spot beam was employed. The
transmit gain of the AMT (30 GHz) is a minimum of 20 dBi with a 12° elevation
beamwidth for elevation angles between 30° and 60°. The receive gain at 20 GHz is a
minimum of 18.8 dBi over a 12° elevation beamwidth for elevation angles between 30°
and 60°. The minimum receive system G/T is better than –6 dB/K over the elevation
beamwidth. The AMT antenna is mechanically steerable in both azimuth and elevation.
Analysis of pilot tone data received by the AMT showed that negligible variations of the
signal arose due to ocean multipath. This is consistent with the relatively narrow
beamwidth (12°) and the fact that the elevation angle was always above 40°. During the
measurement campaign, six significant fades above 10 dB were noted. The deepest fades
(in excess of 30 dB) occurred just after the ship changed direction after a long turn;
suggesting the antenna tracker may have been the source of the fades [Perrins and Rice,
1997]. For the ship oriented azimuth angles associated with the maneuvers, the line-ofsight
was clear for elevation angles as low as 30°. Hence, it did not appear that
shadowing by the superstructure accounted for the observed fades.
9.7 Summary and Recommendations
9.7.1 Fading Depth Due to Sea Surface Reflections
Figure 9-3 through Figure 9-9 may be used to estimate the multipath fading depth at
L-Band (1 to 2 GHz) for the indicated exceedance percentages, antenna gain, and
elevation angle assuming circular polarization. These curves were generated using the
step by step procedure given by (9-15) through (9-21) for circular polarization.
Horizontal polarization may alternately be employed using the tabulations of Table 9-1.