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

12-2
Propagation Effects for Vehicular and Personal Mobile Satellite Systems
0.
5
0.
5
⎪
⎧ ⎡⎛
1 ⎞ ⎛ 1 ⎞ ⎤⎪
⎫
A ( f2
) = A(
f1)
⋅ exp⎨1.
5⋅
⎢ ⎜
⎟ − ⎜
⎟ ⎥⎬
, (12-1)
⎪⎩ ⎢⎣
⎝ f1
⎠ ⎝ f2
⎠ ⎥⎦
⎪⎭
where A ( f1),
A(
f2
) are expressed in dB and represent equal probability attenuations at
frequencies f1, f2
(GHz), respectively. In the scaling from L-Band (1.6 GHz) to K-Band
(19.6 GHz), the expression (12-1) was found to hold over percentages between 1.5% to
20% with a maximum deviation of 2 dB. The concept of “percentage” for the static tree
case represents “the percentage of optically shadowed locations over which
measurements were made.”
12.2.3 Effects of Canopy Branches and Foliage
At UHF (870 MHz), branches of canopies are the dominant cause of attenuation, whereas
at K-Band (20 GHz), the leaf part of the tree is the major cause. For example, assume
that 5 dB attenuation exists for the no-foliage condition at UHF or K-Band. When leaves
are present, the attenuation in dB nominally increases at UHF by a factor of 1.35 to
6.8 dB, whereas at K-Band it increases by a factor of 3.5 to 17.5 dB.
The following static formulations were found applicable:
For 5 dB ≤ A( no foliage) ≤ 14 dB at f = 870MHz
A( foliage)
= 1.
35⋅
A(
no foliage)
. (12-2)
For 5 dB ≤ A( no foliage) ≤ 25 dB at f = 20 GHz
A( foliage) . . [ A( no foliage)]
. 0 578
= 0 351+ 6 825⋅
, (12-3)
where A( foliage), A( no foliage)
are the equal probability values of the attenuation (in
dB) for the foliage and non-foliage conditions, respectively.
12.2.4 Suggestions for Future Efforts
Measurements in the interval between 4 GHz and 20 GHz are not available. Static
canopy attenuation measurements for earth-satellite scenarios should therefore be made at
the intermediate frequencies (e.g., C-Band, X-Band and Ku Band) to extend the validity
of (12-1). This formulation may further be extended for frequencies above 20 GHz.
12.3 Attenuation Due to Roadside Trees: Mobile Case (Chapter 3)
Attenuation distributions are presented for scenarios involving a mobile vehicle with an
antenna mounted on its roof receiving satellite signals along tree-lined roads. The results
presented here are framed in terms of the “percentage of the distance driven over which