JED - June 2014 - 50

E W101
DRFM captures pulse
compression modulation
parameters

Radar pulses
Pulses have matched pulse compression modulation

Jammer pulses
Figure 4. A DRFM-equipped jammer captures the compression modulation on the first pulse and
generates subsequent pulses with matched modulation.

assumes that the jammer pulses do not have the proper pulse
compression modulation. Pulse compression can be achieved by
PIPELINE MODE
either chirping (i.e., frequency modulating) the pulses or apWhen a DRFM-equipped jammer is employed against a
plying a Barker code. In either case, the J/S that a jammer can
radar with a very high duty cycle, such as a Pulse-Doppler
produce is reduced by the same factor as
radar in high-pulse-repetition-frethe compression ratio. This can reduce
quency (PRF) mode, the DRFM can
Pulse Doppler radar range vs. velocity matrix
jamming effectiveness by multiple orcollect data from a second pulse
ders of magnitude, as shown in Figure 4.
before retransmitting an earlier
There are other ways to produce linpulse. See Figure 6. This "pipeJammer signal with
early chirped jamming pulses, but a
lining" mode allows adequate time
frequency matching
DRFM-equipped jammer can measure
to generate the proper jamming
rate of change of
range
the frequency modulation on the radar's
pulse parameters. Note that highpulses (either linear or non-linear moduPRF radars normally operate on a
lation). It can then generate jamming
single frequency to enhance fast
pulses with frequency modulation which
Fourier transform (FFT) processing
Radar
very closely approximates that on the
of received signals. Thus, one pulse
skin
skin return pulses.
looks like any other, and pipe-linreturn
A DRFM-equipped jammer can deing can be successfully employed.
termine the bit rate and the exact
Doppler frequency cells
digital code on the first Barker-coded
WHAT'S NEXT
Figure 5. A DRFM-equipped jammer can generate
pulse received. It can then produce
Next month, we will move on to
false target pulses at frequencies which simulate
jamming pulses for all subsequent skin
a series on radar decoys. Note that
the Doppler shift matching their rate of change of
range.
return pulses which have the proper
there are some important DRFM
Barker code.
developments expected, so we will
In either case, the DRFM improves the achieved J/S by mulprobably return to this subject for an occasional column over
tiple orders of magnitude against pulse-compression radars.
the next few months. For your comments and suggestions,
Range rate/Doppler shift correlation: Pulse-Doppler raDave Adamy can be reached at dave@lynxpub.com. a
dars can detect separating targets and
capture the range history along with
the Doppler frequency history of each
Radar pulses
of those targets. By correlating the
rate of change of range with the Doppler shift, the radar can discriminate
against false targets, allowing it to
continue tracking targets with its true
skin returns. See Figure 5.
DRFM-equipped jammers can set both
the pulse timing and the frequency of
jamming pulses so that they are consisFigure 6. In pipe-lining mode, a DRFM takes more than one pulse interval to complete the
tent with true skin returns, and thus
processing required to produce a matched jamming pulse.
Range cells

The Journal of Electronic Defense | June 2014

50

will allow range-gate-pull-off, rangegate-pull-in and other false target jamming techniques to be effective.
Detailed analysis of Radar Cross
Section (RCS) allows a radar to detect changes in the received return
from a target when false target pulses
are generated by a jammer. By noting
the change, the radar can reject the
newly introduced jamming signals and
re-acquire the true skin return.
Since the most modern DRFMequipped jammers can create very
complex pulses that incorporate multisurface RCS patterns, they can generate
false targets that a radar has great difficultly identifying as false.



JED - June 2014

Table of Contents for the Digital Edition of JED - June 2014

The View From Here
Conferences Calendar
Courses Calendar
From the President
The Monitor
World Report
50 Years of Airborne SIGINT
ACE Program Lays Out Plans for New EW Capabilities
Technology Survey: Spectrum Analyzers
EW 101
NAWCWD Hosts 43rd Annual Collaborative Electronic Warfare Symposium
AOC News
Index of Advertisers
JED Quick Look
JED - June 2014 - cover1
JED - June 2014 - cover2
JED - June 2014 - 3
JED - June 2014 - 4
JED - June 2014 - 5
JED - June 2014 - The View From Here
JED - June 2014 - 7
JED - June 2014 - Conferences Calendar
JED - June 2014 - 9
JED - June 2014 - Courses Calendar
JED - June 2014 - 11
JED - June 2014 - From the President
JED - June 2014 - 13
JED - June 2014 - 14
JED - June 2014 - The Monitor
JED - June 2014 - 16
JED - June 2014 - 17
JED - June 2014 - 18
JED - June 2014 - 19
JED - June 2014 - World Report
JED - June 2014 - 21
JED - June 2014 - 50 Years of Airborne SIGINT
JED - June 2014 - 23
JED - June 2014 - 24
JED - June 2014 - 25
JED - June 2014 - 26
JED - June 2014 - 27
JED - June 2014 - 28
JED - June 2014 - 29
JED - June 2014 - 30
JED - June 2014 - 31
JED - June 2014 - 32
JED - June 2014 - ACE Program Lays Out Plans for New EW Capabilities
JED - June 2014 - 34
JED - June 2014 - 35
JED - June 2014 - 36
JED - June 2014 - Technology Survey: Spectrum Analyzers
JED - June 2014 - 38
JED - June 2014 - 39
JED - June 2014 - 40
JED - June 2014 - 41
JED - June 2014 - 42
JED - June 2014 - 43
JED - June 2014 - 44
JED - June 2014 - 45
JED - June 2014 - 46
JED - June 2014 - 47
JED - June 2014 - 48
JED - June 2014 - EW 101
JED - June 2014 - 50
JED - June 2014 - 51
JED - June 2014 - 52
JED - June 2014 - NAWCWD Hosts 43rd Annual Collaborative Electronic Warfare Symposium
JED - June 2014 - AOC News
JED - June 2014 - 55
JED - June 2014 - 56
JED - June 2014 - Index of Advertisers
JED - June 2014 - JED Quick Look
JED - June 2014 - cover3
JED - June 2014 - cover4
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