JED - November 2016 - 64

E W

twice - for example, the up and down links for a
satellite can be at the same frequency if the two
links have opposite sense circular polarization.
Another polarization consideration is that
small ground or airborne antennas sometimes
have linear polarization - while the spacecraft
antennas are circularly polarized. When one end
of the link has any linear polarization while the
other end of the link has either right hand or
left hand circular polarization, there is a 3-dB
polarization loss.

o

h
ug

ce

an

t
Dis

in

Ra

o
thr

nt
tio
ec ite
r
i
D tell
Sa

Zero Degree Isotherm
Height of
Zero degree
isotherm

Elevation
angle

101

Local Horizon

RAIN LOSS

Figure 2 shows the link loss per kilometer (km)
caused by rain. To use this chart, start with the
frequency on the abscissa. Move vertically to the
line for the rain rate anticipated and then move
Figure 3 The distance over which rain loss applies is the part of the linkleft to the ordinate which gives the rain loss per km. Table
below6the zero degree isotherm
1 identifies the curve on Figure 2 for each of several rainfall
rates. The loss per km is then multiplied by the distance over
5
which the link passes through the rain.
For space links, there is another complication. Out in space
4
there is no rain. Thus the rain loss applies only between the
altitude at which the rain starts and the altitude of the Earth
3
station. Figure 3 shows the applicable geometry. Rain falls
Probability
from the altitude at which the atmosphere is at 0ºC. Above this
2
0.001%
altitude, the rain is frozen, and ice causes negligible attenua0.01%
tion. Consider the elevation angle of the satellite from the Earth
1
64
terminal. We can calculate the length of the path through the
0.1%
rain as the height of the zero-degree isotherm divided by the
1%
sine of this angle. Note that if the link is between a satellite
10
20
30
40
50
60
70
80
and an aircraft, the "Earth terminal" is at the altitude of the
Latitude (degrees)
aircraft. Since rain attenuation is considered probabilistically
rather that calculated moment to moment, the chart in Figure
Figure 4: The probability that the zero-degree isotherm falls below a
4 (probability of height of the zero degree isotherm vs. latitude)
given altitude is a function of the latitude.
Figure 4 The probability that the zero degree isotherm falls below a given
is very helpful. If, for example, we are
altitude is a function of the latitude.
considering the 99% reliability of a link
performance level, we would start at the
latitude of the Earth station and go up
to the 1% line - then left to the ordinate
to find the expected height of the zero
Communications Band Receiver Range Extension Products
degree isotherm. Let's take an example:
We are at 40° latitude. The 1% line is
●Adaptable Multi-Couplers
about 2 km altitude. The satellite is 30°
●Programmable Notch Filters
-Selectively attenuate interfering
above the local horizon. The sine of 30° is
signals
0.5. The range through the rain is thus 2
We also design & manufacture an
-High power versions available
km/0.5 = 4 km. If there is heavy rain and
extensive line of switch matrices
●Co-Located Cancellers
the link is at 15 GHz, the rain loss (from
& RF signal routers!
-Referenced & referenceless
Figure 2) will be 0.73 dB/km multiplied
versions
by 4 km, which is 2.9 dB.
-Attenuate co-located transmitters
●Non-Reflective Limiters
WHAT'S NEXT
-These receiver protectors do not
Next month, we will continue our discusreradiate the limited signal
sion of space EW with a few link-loss calculations for typical EW applications. For your
comments and suggestions, Dave Adamy can
be reached at dave@lynxpub.com. a
The Journal of Electronic Defense | November 2016

Height of zero degree Isotherm (km)

Figure 3: The distance over which rain loss applies is the part of the link below the zero
degree isotherm.

ARS Products

677599_ARSProducts.indd 1

2015-08-31 8:06 AM



JED - November 2016

Table of Contents for the Digital Edition of JED - November 2016

The View From Here
Conferences Calendar
Courses Calendar
From the President
The Monitor
World Report
US Helicopter EW Programs
53rd Annual AOC International Symposium and Convention Guide
Conference Report
Threat Monitor
EW 101
AOC News
Index of Advertisers
JED Quick Look
JED - November 2016 - cover1
JED - November 2016 - cover2
JED - November 2016 - 3
JED - November 2016 - 4
JED - November 2016 - 5
JED - November 2016 - The View From Here
JED - November 2016 - 7
JED - November 2016 - Conferences Calendar
JED - November 2016 - 9
JED - November 2016 - Courses Calendar
JED - November 2016 - 11
JED - November 2016 - From the President
JED - November 2016 - 13
JED - November 2016 - 14
JED - November 2016 - The Monitor
JED - November 2016 - insert1
JED - November 2016 - insert2
JED - November 2016 - 16
JED - November 2016 - 17
JED - November 2016 - 18
JED - November 2016 - 19
JED - November 2016 - 20
JED - November 2016 - 21
JED - November 2016 - 22
JED - November 2016 - 23
JED - November 2016 - World Report
JED - November 2016 - 25
JED - November 2016 - US Helicopter EW Programs
JED - November 2016 - 27
JED - November 2016 - 28
JED - November 2016 - 29
JED - November 2016 - 30
JED - November 2016 - 31
JED - November 2016 - 32
JED - November 2016 - 33
JED - November 2016 - 34
JED - November 2016 - 35
JED - November 2016 - 36
JED - November 2016 - 53rd Annual AOC International Symposium and Convention Guide
JED - November 2016 - 38
JED - November 2016 - 39
JED - November 2016 - 40
JED - November 2016 - 41
JED - November 2016 - 42
JED - November 2016 - 43
JED - November 2016 - 44
JED - November 2016 - 45
JED - November 2016 - 46
JED - November 2016 - 47
JED - November 2016 - 48
JED - November 2016 - 49
JED - November 2016 - 50
JED - November 2016 - 51
JED - November 2016 - 52
JED - November 2016 - 53
JED - November 2016 - 54
JED - November 2016 - 55
JED - November 2016 - 56
JED - November 2016 - Conference Report
JED - November 2016 - 58
JED - November 2016 - 59
JED - November 2016 - Threat Monitor
JED - November 2016 - 61
JED - November 2016 - 62
JED - November 2016 - EW 101
JED - November 2016 - 64
JED - November 2016 - 65
JED - November 2016 - AOC News
JED - November 2016 - 67
JED - November 2016 - 68
JED - November 2016 - Index of Advertisers
JED - November 2016 - JED Quick Look
JED - November 2016 - cover3
JED - November 2016 - cover4
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