# JED - October 2016 - 68

```
EW 101

Space EW - Part 5

Path Loss from Satellite

T

he total path loss to or from
a satellite includes the lineof-sight loss, atmospheric
loss, antenna misalignment
loss, polarization loss and
rain loss.

Range to Satellite
Elevation
above
Local Horizon
Ground
Station

Height of
Satellite

d

A

90°

RE

LINE-OF-SIGHT LOSS

Local Horizon

B
RE

b

a
D

Center
of Earth

Last month, we calculated the range
Figure 1: The range to any Earth satellite can be calculated from a plane triangle formed by the
to a synchronous satellite, and we calcusatellite, a ground station and the center of the Earth.
lated the loss using the above formula.
Figure 1 shows a more general form of the range calcula100
tion using the plane triangle
formed by the satellite, the
ground station and the center
10
of the Earth. Let's determine
the range from a satellite with
a circular orbit period of two
1
hours to a ground station that
sees the satellite 20 degrees
0.1
above its local horizon - using
the law of sines for plane triTotal (Standard Air)
angles. In Figure 1:
0.01
* Side a is the radius of the
Total (Dry Air)
Earth (6371 km).
Water Vapor
* The angle A is the angle from
0.001
the ground station to the
100
10
200
1
6
20
40 60
2
4
center of the Earth as seen
Frequency (GHz)
from the satellite.
Figure 2: Atmospheric attenuation per km within the atmosphere is a function of frequency and humidity.
Atmospheric Attenuation (dB / km)

The Journal of Electronic Defense | October 2016

68

The primary component of link loss to
or from a satellite is associated with the
extremely long range. Since the satellite
is in space, this loss is the "space loss,"
also called the "line-of-sight" loss, determined from the formula:
L = 32.44 + 20 log(d) + 20 log(F)
Where:
L = the line of sight loss in dB
d = the transmitter to receiver distance
in km
F = the transmission frequency in MHz

Figure 2: Atmospheric attenuation per km within the atmosphere is a function of
frequency and humidity.

```

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