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

Attenuation Due to Roadside Trees: Mobile Case 3-3
Relative Power (dB)
Phase (deg)
5
0
-5
-10
-15
-20
180
135
90
45
0
-45
-90
-135
-180
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
Time (s)
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
Time (s)
Figure 3-2: Time-series of 1.5 GHz fades (top) and phases (bottom) over a one second
period at a sampling rate of 1 KHz. Measurements were taken of transmissions from
MARECS-B2 at 40° elevation along a highway with roadside trees in central Maryland
where the satellite line-of-sight was shadowed.
We show in Figure 3-3 an example of the variability of the minimum, maximum, and
average fades over an approximate 10 minute period (approximately 10 km) pertaining to
20 GHz measurements of transmissions from the Advanced Communications Technology
Satellite (ACTS) in Bastrop, Texas. The tree genus was predominantly Loblolly Pine
(evergreen tree) and the elevation angle was approximately 55°. The central, red curve
corresponds to the average signal level of 1000 samples taken over a one-second period
(1 KHz sampling rate). The upper and lower curves correspond to the maximum and
minimum signal level values obtained from the 1000 samples measured each second,
respectively. Maximum values of three to four dB relative to the non-shadowed line-ofsight
case arise because of constructive interference caused by multipath scatter by the
foliage and branches. Large signal-level-drops to –20 dB and lower are due
predominantly to canopy attenuation. The cumulative distribution for this run is
described in Section 3.4.3 (Figure 3-12).