JED - December 2017 - 81

EW 101

Next Generation EW - Part 2

J/S and Burn-through Problems
By Dave Adamy

SELF-PROTECTION JAMMING

Figure 1 shows a self-protection jamming situation. The
target is an aircraft with a radar cross section (RCS) of 10 m2.
It has a self-protection jammer with 10 watts (which is 50 dBm)
transmitter power and an antenna with 6 dBi gain toward the
hostile radar. The effective radiated power (ERP) of the jammer
is the sum of the transmitter power (in dBm) and the antenna
gain (in dBi). The radar has a transmitter power of 100 kW
(which is 80 dBm) and the boresight gain of its antenna is 30
dBi. Thus the ERP of the radar is 110 dBm. The ERP of the jammer is the sum of its transmitter power and its antenna gain;
The ERP is thus 56 dBm.
Note that we are adding "dBm" to "dBi" and coming up with
an answer in dBm. This can be confusing, but is true because
of some underlying units that we have ignored. If you go back
to the underlying definitions of the dBm and dBi values, the
units work out. We have ignored these underlying definitions
out of pure laziness, but be assured that in these equations,
dB, dBm and dBi can be added with impunity.
The target aircraft is 10 km from the radar, so the jammer it
carries is at the same distance.
The formula for the jamming to signal ratio achieved by
self-protection jamming is:
J/S = ERPJ - ERPS + 71 + 20 log R - 10 log RCS
Where: J/S is the jamming to signal to noise ratio in dB,
ERPJ is the effective radiated power of the jammer
in dBm,
ERPS is the effective radiated power of the jammed

Plugging the values for this problem into this equation
yields:
J/S = 56 dBm - 110 dBm + 71 + 20 log 10 - 10 log 10
= 56 - 110 + 71 +20 -10 = 27 dB

SELF PROTECTION BURN-THROUGH
The range from the radar at which the radar can reacquire its
target in the presence of jamming is called the "burn-through
range." Figure 2 shows the target approaching the radar -
which reduces the jamming to signal ratio. Because the J/S at
which burn-through occurs varies with the type of jamming
employed, the term for J/S required is important. In many
cases, the required value is 0 dB, but the author found himself
ignoring the J/S term when that value was used. Therefore, for

RBT
Radar Signal

J

Jammer Signal

RADAR

RCS = 10 m 2

ERPS = 110 dBm

ERPJ = 56 dBm
Range at which
there is 2 dB J/S

Figure 2: R BT for this problem is the range at which the jammer can only
Figure 2: RBT for this problem is the range at which the jammer can only
achieve 2 dB J/S.
achieve 2 dB J/S.

The Journal of Electronic Defense | December 2017

T

his month, we will set
PJ = 100 W = 50 dBm
some typical values on
G = 6 dB i
the variables in the
PS = 100 kW = 80 dBm
10 km
G = 30 dB i
equations we discussed
J
last month. Note that
RADAR
these values represent
RCS = 10 m2
the typical specifications of older
hostile tracking radars. Later, we
Figure 1: The target aircraft, with a self-protection jammer is 10 km from the hostile radar, which has
will deal with older acquisition
the main beam of its antenna directed at the target.
radars and modern radars, which
Figure 1: The target aircraft, with a self-protection jammer is 10 km from the
have significantly different specihostile radar, which has the main beam of its antenna directed at the target.
fications. Note that the specifications used here are not for
radar in dBm,
any specific threat system; the important points are how the
R is the range from the radar to the target (and
numbers are used in calculations.
jammer) in km,
RCS is the radar cross section of the target in m2.

81



JED - December 2017

Table of Contents for the Digital Edition of JED - December 2017

The View From Here
Conferences Calendar
Courses Calendar
From the President
The Monitor
Washington Report
World Report
An Approach to UAV-Based ELINT
Combined EW and Cyber Event Illuminates Important Issues and Disconnects
Technology Survey: RF Tuners and Tuner Modules for SIGINT Applications
AOC EW Singapore 2018 Preview
Report from the 2017 AOC CEMA Conference
New Products
Recounting the History of the EW Working Group
EW 101
AOC 2017 Annual Award Winners
AOC News
Index of Advertisers
JED Quick Look
JED - December 2017 - intro
JED - December 2017 - cover1
JED - December 2017 - cover2
JED - December 2017 - 3
JED - December 2017 - 4
JED - December 2017 - 5
JED - December 2017 - The View From Here
JED - December 2017 - 7
JED - December 2017 - Conferences Calendar
JED - December 2017 - 9
JED - December 2017 - Courses Calendar
JED - December 2017 - 11
JED - December 2017 - From the President
JED - December 2017 - 13
JED - December 2017 - 14
JED - December 2017 - insert1
JED - December 2017 - insert2
JED - December 2017 - The Monitor
JED - December 2017 - 16
JED - December 2017 - 17
JED - December 2017 - 18
JED - December 2017 - 19
JED - December 2017 - 20
JED - December 2017 - 21
JED - December 2017 - 22
JED - December 2017 - 23
JED - December 2017 - Washington Report
JED - December 2017 - 25
JED - December 2017 - World Report
JED - December 2017 - 27
JED - December 2017 - An Approach to UAV-Based ELINT
JED - December 2017 - 29
JED - December 2017 - 30
JED - December 2017 - 31
JED - December 2017 - 32
JED - December 2017 - 33
JED - December 2017 - 34
JED - December 2017 - 35
JED - December 2017 - 36
JED - December 2017 - 37
JED - December 2017 - 38
JED - December 2017 - 39
JED - December 2017 - 40
JED - December 2017 - Combined EW and Cyber Event Illuminates Important Issues and Disconnects
JED - December 2017 - 42
JED - December 2017 - 43
JED - December 2017 - 44
JED - December 2017 - 45
JED - December 2017 - 46
JED - December 2017 - 47
JED - December 2017 - 48
JED - December 2017 - Technology Survey: RF Tuners and Tuner Modules for SIGINT Applications
JED - December 2017 - insert3
JED - December 2017 - insert4
JED - December 2017 - 50
JED - December 2017 - 51
JED - December 2017 - 52
JED - December 2017 - 53
JED - December 2017 - 54
JED - December 2017 - 55
JED - December 2017 - 56
JED - December 2017 - 57
JED - December 2017 - 58
JED - December 2017 - 59
JED - December 2017 - 60
JED - December 2017 - 61
JED - December 2017 - 62
JED - December 2017 - AOC EW Singapore 2018 Preview
JED - December 2017 - 64
JED - December 2017 - 65
JED - December 2017 - 66
JED - December 2017 - 67
JED - December 2017 - Report from the 2017 AOC CEMA Conference
JED - December 2017 - 69
JED - December 2017 - 70
JED - December 2017 - 71
JED - December 2017 - 72
JED - December 2017 - 73
JED - December 2017 - New Products
JED - December 2017 - 75
JED - December 2017 - 76
JED - December 2017 - Recounting the History of the EW Working Group
JED - December 2017 - 78
JED - December 2017 - 79
JED - December 2017 - 80
JED - December 2017 - EW 101
JED - December 2017 - 82
JED - December 2017 - 83
JED - December 2017 - 84
JED - December 2017 - AOC 2017 Annual Award Winners
JED - December 2017 - 86
JED - December 2017 - 87
JED - December 2017 - 88
JED - December 2017 - 89
JED - December 2017 - 90
JED - December 2017 - 91
JED - December 2017 - 92
JED - December 2017 - 93
JED - December 2017 - 94
JED - December 2017 - AOC News
JED - December 2017 - 96
JED - December 2017 - Index of Advertisers
JED - December 2017 - JED Quick Look
JED - December 2017 - cover3
JED - December 2017 - cover4
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