JED - January 2018 - 31

EW 101

Next Generation EW - Part 3

Stand-off Jamming of Legacy
Acquisition Radars
By Dave Adamy

J/S RATIO
The jammer is trying to prevent the radar from acquiring a target with RCS = 10 m2 at a range of 10 km. From last month, we know
that the stand-off jamming J/S equation is:
J/S = ERPJ - ERPS + 71 + GS - GM - 20 log R J + 40 log RT
- 10 log RCS
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,
R J is the range from the radar to the jammer in km,
RT is the range from the radar to the target in km,
and
RCS is the radar cross section of the target in m2.
Plugging the values from Figure 1 into this equation gives:
J/S = 78 - 112 + 71 + 8 - 29 - 29.5 + 40 - 10 = 16.5 dB

RCS = 10 m 2
10 km
SPOON REST
RADAR

ERPS = 112 dBm
S/L = -21 dB

30 km

J

Lethal
range
of weapon

PJ = 1 KW
GJ = 18 dB

Figure 1: The stand-off jammer is located 30 km from a Spoon Rest radar in a side lobe that is 21 dB below the radar's main-beam bore-sight gain.

.

The Journal of Electronic Defense | January 2018

I

t requires seven to ten dB more jamming power to
break the lock of a tracking radar than it does to
prevent that radar from acquiring a target. Since
jammer effectiveness from a stand-off jammer is
reduced because it is far from the jammed radar and
because it must normally jam into the side lobes of
that radar, stand-off jammers normally operate against
acquisition radars or acquisition modes. Let's look at the
problem of stand-off jamming against a typical legacy
acquisition radar.
Figure 1 shows a P-12 Spoon Rest radar being jammed
by a stand-off jammer located 30 km away in the radar's
side lobes. From open literature, the transmitter power of
the radar is given as 200 kw (83 dBm), its antenna boresight gain is given as 29 dBi and its average side lobe is
21 dB below the boresight gain. This means that the radar
ERP is 112 dBm, and the side lobe gain is 8 dBi. For this
problem, we will take these values as accurate. We will
assume the same stand-off jammer we used to jam the
tracking radar last month (i.e., 1-kW transmitter power
and 18 dB antenna gain). The ERP of the jammer is thus
78 dBm.

31



JED - January 2018

Table of Contents for the Digital Edition of JED - January 2018

The View From Here
Conferences Calendar
Courses Calendar
From the President
The Monitor
Washington Report
World Report
Thinking Through Collaborative Electronic Warfare
Report from the 6th Annual AOC Pacific Conference
EW 101
AOC News
Highlights from the AOC 54th Annual International Symposium & Convention
Index of Advertisers
JED Quick Look
JED - January 2018 - Intro
JED - January 2018 - cover1
JED - January 2018 - cover2
JED - January 2018 - 3
JED - January 2018 - 4
JED - January 2018 - 5
JED - January 2018 - The View From Here
JED - January 2018 - insert1
JED - January 2018 - insert2
JED - January 2018 - 7
JED - January 2018 - Conferences Calendar
JED - January 2018 - 9
JED - January 2018 - Courses Calendar
JED - January 2018 - 11
JED - January 2018 - From the President
JED - January 2018 - 13
JED - January 2018 - 14
JED - January 2018 - The Monitor
JED - January 2018 - 16
JED - January 2018 - 17
JED - January 2018 - 18
JED - January 2018 - 19
JED - January 2018 - Washington Report
JED - January 2018 - World Report
JED - January 2018 - Thinking Through Collaborative Electronic Warfare
JED - January 2018 - 23
JED - January 2018 - 24
JED - January 2018 - 25
JED - January 2018 - 26
JED - January 2018 - 27
JED - January 2018 - 28
JED - January 2018 - Report from the 6th Annual AOC Pacific Conference
JED - January 2018 - 30
JED - January 2018 - EW 101
JED - January 2018 - 32
JED - January 2018 - AOC News
JED - January 2018 - Highlights from the AOC 54th Annual International Symposium & Convention
JED - January 2018 - 35
JED - January 2018 - 36
JED - January 2018 - Index of Advertisers
JED - January 2018 - JED Quick Look
JED - January 2018 - cover3
JED - January 2018 - cover4
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