# JED - September 2017 - 45

```EW 101

Space EW Part 16

EW Operations from Space

In the last two "EW 101" columns, we discussed the intercept of hostile ground signals from space. This month, we will
discuss the jamming of hostile ground signals from space -
specifically communications jamming. We have discussed jamming within the atmosphere many times, but doing so from
space requires that we consider the geometric dictates of the
orbit from which the jamming takes place.

JAMMING FROM A SATELLITE
The effectiveness of a jammer requires that it produce the
power (ERP), and that it be close enough to the jammed receiver to keep the propagation losses low enough. Satellites,
by their nature are far away from what is happening on the
Earth - so jamming from space is not easy. That said, space is a
well-established EW battlespace, so let's get on with it.
For convenience, we will use the same orbit we have used
in recent discussions: a 300-km-high circular orbit with an
inclination of 60°. We will jam a target
at 35° North latitude and 105° East lonDistance
gitude. From earlier columns, we know
from
that the period of the orbit is 90.364
satellite
minutes, and that if it passes directly
to target
over the target. It can see the target for
19.3 minutes. We also know that the distance from the target to the satellite at
the stated location is 828 km. We will assume that the satellite has a two-meter
parabolic antenna that can be pointed
with 1° accuracy. The satellite geometry
is shown in Figure 1.
Sub-vehicle

COMMUNICATIONS JAMMING
Consider the communications jamming engagement shown in Figure 2.
Although this figure shows one desired
signal transmitter and one target receiver, the actual target is a network of hostile transceivers operating at 400 MHz

with whip antennas. One transceiver is transmitting with an
effective radiated power (ERP) of 10 Watts, and all of the others in the network are receiving. The average distance to each
receiving station is 5 km. The sub-vehicle point of the satellite
is 30° North Latitude and 100° East Longitude. The jammer
transmitter output power is 100 Watts.
The 3-dB beam-width and bore-sight gain of the jamming
antenna and the antenna misalignment loss are determined by
formulas from the July 2017 "EW101" column:
Beam-width: BW = anti-log[ (86.8 - 20 log D - 20 logF)/20]
Where: BW is the 3-dB beam-width in degrees
D is the dish diameter in meters
F is the frequency in MHz
BW = anti-log[(86.8 - 6.0 - 52.0)/20} = 27.5°
Gain:
Where:

G = -42.2 + 20 Log D + 20 Log F
G is the bore-sight gain in dBi
G = -42.2 + 6.0 + 52.0 = 15.8 dBi

North
Pole

Longitude
Threat
location
Latitude
of threat

point

Latitude
of sub-vehicle
point

Center
of Earth

Fig. 1: The propagation distance from the satellite to the target depends on the orbital geometry.

The Journal of Electronic Defense | September 2017

JAMMING OF A GROUND SIGNAL FROM A SATELLITE

45

```

# JED - September 2017

The View from Here
Conferences Calendar
Courses Calendar
From the President
The Monitor
Washington Report
World Report
Army Brigade Electronic Warfare Weapons Teams Learn New Lessons at NTC
Technology Survey: Counter-UAS Systems
EW 101
JED Quick Look
JED - September 2017 - intro
JED - September 2017 - cover1
JED - September 2017 - cover2
JED - September 2017 - 3
JED - September 2017 - 4
JED - September 2017 - 5
JED - September 2017 - The View from Here
JED - September 2017 - 7
JED - September 2017 - Conferences Calendar
JED - September 2017 - 9
JED - September 2017 - Courses Calendar
JED - September 2017 - 11
JED - September 2017 - From the President
JED - September 2017 - 13
JED - September 2017 - 14
JED - September 2017 - The Monitor
JED - September 2017 - insert1
JED - September 2017 - insert2
JED - September 2017 - 16
JED - September 2017 - 17
JED - September 2017 - Washington Report
JED - September 2017 - 19
JED - September 2017 - World Report
JED - September 2017 - 21
JED - September 2017 - Army Brigade Electronic Warfare Weapons Teams Learn New Lessons at NTC
JED - September 2017 - 23
JED - September 2017 - 24
JED - September 2017 - 25
JED - September 2017 - 26
JED - September 2017 - 27
JED - September 2017 - 28
JED - September 2017 - 29
JED - September 2017 - 30
JED - September 2017 - 31
JED - September 2017 - 32
JED - September 2017 - 33
JED - September 2017 - 34
JED - September 2017 - 35
JED - September 2017 - 36
JED - September 2017 - Technology Survey: Counter-UAS Systems
JED - September 2017 - 38
JED - September 2017 - 39
JED - September 2017 - 40
JED - September 2017 - 41
JED - September 2017 - 42
JED - September 2017 - 43
JED - September 2017 - 44
JED - September 2017 - EW 101
JED - September 2017 - 46
JED - September 2017 - 47
JED - September 2017 - 48
JED - September 2017 - Index of Advertisers
JED - September 2017 - JED Quick Look
JED - September 2017 - cover3
JED - September 2017 - cover4
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