# JED - November 2017 - 67

E W101

J

Jammer Signal

nal to noise ratio is no longer adequate
to protect the target, but it can be as
to protect the target, burn-through ocmuch as 20 to 40 dB. Now, we determine
R is the range from the radar to
Figure
Self(and
protection
jamming
uses
jammerforonburn-through
the target and
transmits directly
curs.
The aequation
the burn-through
range frominto
the range
the1:
target
jammer) in km
the main
thesection
jammed
range is presented here in two parts:
term with the formula:
RCS is beam
cross
of
first the range term in the J/S formula
the target in m2
R BT = Anti-log {[20 log R BT[ / 20}
at the burn-through range, then the actual burn-through range.
As the target (an aircraft in this
This equation looks strange, but note
The formula for the range term (at
that we are taking the anti-log of the
burn-through) is:
jammer approaches with it. Another imvalue of 20 log R BT.
portant point is that the bore-sight of
20 log R BT = ERPS - ERPJ - 71
the radar antenna is pointed directly at
STAND-OFF JAMMING
+ 10 log RCS + J/S Req
the target it is tracking (and hence the
Figure 3 shows the stand-off jamjammer). Both of these operational facming geometry. Note that the jamming
Where: R BT is the range from the radar
tors mean that the jammer can provide a
aircraft is a high value/low inventory
to the target at burn-through
very large jamming to signal ratio (J/S).
asset, so we want to keep it beyond
in km
In general, a self-protection jammer can
the lethal range of the weapon associJ/S Req is the J/S value at
deliver enough power to break the lock
ated with the radar we are jamming.
which the jammer can no longer
of a hostile radar. This requires 7 to 10
This diagram shows one jammer proeffectively jam the radar
dB more power than would be required
tecting one target against one radar,
to prevent the radar from acquiring the
but in the actual application there are
The required J/S for burn-through
target.
two jamming aircraft flying coordinated
varies with the type of jamming emThe J/S equation shows that the efrace track patterns to protect multiple
ployed. Sometimes, 0 dB J/S is adequate
fectiveness of the jamming increases with range and the ERP of the
jammer; also that it decreases with
the ERP of the radar and with the
Radar Signal [Reduces by 4] R
RCS of the target.

J

The range from the radar at
which it can reacquire its target in
the presence of jamming is called
the "burn-through range." Figure
2 shows that the strength of the
radar return signal (i.e., the "skin
return") increases as the square of
the diminishing distance, while
the strength of the jamming signal
increases by only the square of the
diminishing distance. When the sig-

Jammer Signal [Reduces by 2] R

Target (& Jammer)

Rcvd Pwr

SELF PROTECTION
BURN-THROUGH

Jammer
Skin Return
Range

Range at which
there is no longer

Figure 2: The jamming to signal ratio reduces as the target and the jammer approach the radar. "Burn
through" occurs then the radar can reacquire the target in the presence of jamming.
Figure 2: The jamming to signal ratio reduces as the target and the jammer approach
the radar. "Burn through" occurs then the radar can reacquire the target in the presence
of jamming.

The Journal of Electronic Defense | November 2017

Figure 1: Self protection jamming uses a jammer on the target and transmits directly into the main beam of the jammed radar.

67

# JED - November 2017

The View From Here
Conferences Calendar
Courses Calendar
From the President
The Monitor
World Report
Forecast: Future of DIRCM
Sensor Fusion for 4th Gen Fighters
54th Annual AOC International Symposium and Convention Guide
EW 101
AOC News
JED Quick Look
JED - November 2017 - intro
JED - November 2017 - cover1
JED - November 2017 - cover2
JED - November 2017 - 3
JED - November 2017 - 4
JED - November 2017 - 5
JED - November 2017 - The View From Here
JED - November 2017 - 7
JED - November 2017 - Conferences Calendar
JED - November 2017 - 9
JED - November 2017 - Courses Calendar
JED - November 2017 - 11
JED - November 2017 - From the President
JED - November 2017 - 13
JED - November 2017 - 14
JED - November 2017 - insert1
JED - November 2017 - insert2
JED - November 2017 - The Monitor
JED - November 2017 - 16
JED - November 2017 - 17
JED - November 2017 - 18
JED - November 2017 - 19
JED - November 2017 - 20
JED - November 2017 - 21
JED - November 2017 - 22
JED - November 2017 - 23
JED - November 2017 - World Report
JED - November 2017 - 25
JED - November 2017 - Forecast: Future of DIRCM
JED - November 2017 - 27
JED - November 2017 - 28
JED - November 2017 - 29
JED - November 2017 - 30
JED - November 2017 - 31
JED - November 2017 - 32
JED - November 2017 - 33
JED - November 2017 - 34
JED - November 2017 - Sensor Fusion for 4th Gen Fighters
JED - November 2017 - 36
JED - November 2017 - 37
JED - November 2017 - 38
JED - November 2017 - Technology Survey: ELINT Receivers
JED - November 2017 - 40
JED - November 2017 - 41
JED - November 2017 - 42
JED - November 2017 - 43
JED - November 2017 - 44
JED - November 2017 - 45
JED - November 2017 - 46
JED - November 2017 - 47
JED - November 2017 - 48
JED - November 2017 - 54th Annual AOC International Symposium and Convention Guide
JED - November 2017 - 50
JED - November 2017 - 51
JED - November 2017 - 52
JED - November 2017 - 53
JED - November 2017 - 54
JED - November 2017 - 55
JED - November 2017 - 56
JED - November 2017 - 57
JED - November 2017 - 58
JED - November 2017 - 59
JED - November 2017 - 60
JED - November 2017 - 61
JED - November 2017 - 62
JED - November 2017 - 63
JED - November 2017 - 64
JED - November 2017 - 65
JED - November 2017 - EW 101
JED - November 2017 - 67
JED - November 2017 - 68
JED - November 2017 - AOC News
JED - November 2017 - 70
JED - November 2017 - 71
JED - November 2017 - 72
JED - November 2017 - Index of Advertisers
JED - November 2017 - JED Quick Look
JED - November 2017 - cover3
JED - November 2017 - cover4
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