JED - December 2017 - 83

E W101
the problems this month, we will use 2 dB for the required J/S
at burn through.
The formula for the range term (at burn-through) is:

RCS = 10 m 2
5 km

20 log RBT = ERPS - ERPJ - 71 + 10 log RCS + J/S Req
RADAR

Where: RBT is the range from the RADAR to the target at
burn-through in km,
J/S Req is the J/S value at which the jammer can no
longer effectively jam the radar.

To solve this term for the burn through range, we use the
formula:

J
Lethal
Range
of Weapon

PJ = 1 KW
GJ = 18 dB

Figure 3: The stand-off jammer is located 30 km from the hostile radar
Figure
3: The
stand-off
jammer
is located
km from
the hostile
in
in a side
lobe,
which
is 20
dB below
the 30
radar's
main
beamradar
boresight
a side lobe, which is 20 dB below the radar's main beam boresight gain.
gain.

The formula for the jamming to signal ratio achieved in
stand-off jamming is:
J/S = ERPJ - ERPS + 71 + GS - GM - 20 log RJ + 40 log RT - 10
log RCS

RBT = Anti-log {[20 log RBT[ / 20}
Plugging in our values gives:
RBT = Anti-log {-5/ 20} = 0.25 km or 250 meters

STAND-OFF JAMMING
Figure 3 shows a typical stand-off jamming situation. The
hostile radar and the target aircraft are the same as for the
self-protection problem. Because a stand-off jammer must
transmit into the target radar's side lobes, we need to define
the radar antenna side-lobe level. This is typically shown in a
database as the relative strength (in dB) of the average side
lobe compared to the radar antenna's main beam bore-sight
gain. If the average side lobe level is 20 dB below the boresight
gain, this would be stated as:
S/L = -20 dB as shown in Figure 3. This makes the side lobe
gain 10 dBi
The target aircraft has no jammer. The jamming aircraft has
a large jammer with 1 kW (60 dBm) transmitter power and 18
dB antenna gain, so its ERP is 78 dBm.
The hostile radar controls a missile which is assumed to have
a 30 km lethal range, so our jamming aircraft flies just outside
that range. We will set the range to the jammer as 30 km and we
will move the target aircraft into 5 km from the radar.

Where: J/S is the jamming to signal noise in dB,
ERPJ is the effective radiated power of the jammer in
dBm,
ERPS is the effective radiated power of the jammed
radar in dBm,
GS is the side lobe gain of the radar antenna in dBi,
GM is the main lobe bore-sight gain of the radar antenna in dBi,
RJ is the range from the radar to the jammer in km,
RT is the range from the radar to the target in km,
RCS is the radar cross section of the target in m2.
Plugging the values from Figure 3 into this equation gives:
J/S = 78 - 110 + 71 + 10 - 30 - 29.5 + 28 - 10 = 7.5 dB

STAND-OFF BURN-THROUGH
As shown in Figure 4, the burn-through range is the distance from the target to the radar when the jammer can only
provide 2 dB J/S. Since the range from the stand-off jammer to
the radar is assumed to remain constant through the engagement, the burn-through range is only a function of the range
from the radar to the target. The formula for the range to the
target term (at burn-through) is:
40 log RBT = ERPS - ERPJ - 71 - GS + GM + 20 log RJ + 10 log
RCS + J/S Req

R BT

Plugging our values into this equation gives:

GM = 30 dBi

40 log RBT = 110 - 78 - 71 - 10 + 30 + 29.5 + 10 + 2 = 22.5

Radar Signal
RADAR

S/L = -20 dB

30 km

Jammer
S

ignal

GS = 10 d

Bi

Range at
which jammer
provides 2 dB J/S

Jamm
e
remain r Range
s cons
tant

J
Jammer flies
small race track
pattern

Figure 4: The target approaches the radar while the jammer remains
effectively stationary. The J/S provided by the jammer thus reduces
Figure 4:the
The engagement
target approaches
radar
while to
the target
jammer remains
during
asthethe
radar
range effectively
reduces.stationary.

The J/S provided by the jammer thus reduces during the engagement as the radar to target
range reduces.

The formula for the burn through range solves the range
term for the actual range:
RBT = Anti-log {22.5 / 40} = .563 km = 563 meters

WHAT'S NEXT
Next month, we will continue our discussion of legacy EW
threats and countermeasures with a problem in which an acquisition radar is jammed. For your comments and suggestions,
Dave Adamy can be reached at www.lynxpub.com. a

The Journal of Electronic Defense | December 2017

Plugging the values from this engagement into this formula
gives:
20 log RBT = 110 dBm - 56 dBm - 71 + 10 log 10 + 2 dB
= 110 - 56 - 71 + 10 + 2 = -5

ERPS = 110 dBm

83


http://www.lynxpub.com

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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