JED - June 2015 - 39

TECHNOLOGY SURVEY
A SAMPLING OF RWRs AND ESM SYSTEMS
By Ollie Holt

Arrays (AESAs). This allows the radar to revisit the target
at more random times vs. a predictable scan pattern associated with mechanically steered radars. In addition, modern radars are becoming more frequency agile. Instead of
only changing the operating frequency when they are being
jammed, advanced radars can change frequency on every
pulse or Coherent Processing Interval (CPI). Sometimes only
a single radar pulse might be observed by an ES system.
Because the frequency may change on every pulse and the
revisit rate can continually change, the traditional ES approach of grouping like detections and developing an identification based on those parameters becomes less effective.
The only parameter that is currently fixed is angle. By
measuring the threat signal's angle of arrival, an ES system
can group and possibly identify the seemingly random detections. This means that future ES systems must provide angle
measurements that are much better than the current quadrant measurements provided in many of today's systems.
In response to the radar developments described above,
the ES system market is starting to see a new concept developing - Cognitive EW. This trend reflects the desire that
the EW system of the future be able to determine the intent
of the threat system by reading the detections and inferring from the information measured what the threat radar
is trying to do. Is the radar trying to determine range? If so,
can the EW system do something to prevent that from happening? Is the radar trying to determine angle or velocity,
and if so, what can be done to deny it or delay that from occurring? The ES system may possibly need to perform these
decisions on a single pulse or even within a single pulse,
and it will no longer be able to depend on a database of
detected parameters to identify the threat. Instead it will
need to try to determine the threat's intent and react to
that intent, and it will need to do this on a pulse-to-pulse
basis. Similarly, new ES systems are going to require much
wider instantaneous bandwidths to detect these frequencyagile signals. Emerging threat systems may have agilities in
the gigahertz range. Scanning, narrow-band ES systems will
be hard pressed to detect these RF-agile, wide-band threat
radars unless the ES systems also have very wide instantaneous bandwidths with precision angle on every measurement. They are also going to need to take action quickly,
even within a pulse for long-pulse-width radar modes and
within a CPI for Pulse Doppler modes.
In next month's JED, our technology survey will examine SIGINT tuners.

The Journal of Electronic Defense | June 2015

T

his month's technology survey covers Radar
Warning Receivers (RWRs) and Electronic
Support Measures (ESM) receivers. These are
electronic support (ES) systems and should not
be confused with SIGINT systems. ES systems
focus on providing situational awareness and
threat warning by detecting, identifying and locating radar
emitters and cueing a countermeasures system. SIGINT
receivers are more focused on data collection for on-board
or off-board data analysis.
In this discussion, we are going to group RWRs and ESM
systems and refer to them as ES systems. We will discuss
how a typical ES system works and the technical challenges
they face in the future.
Current ES systems scan the frequency range in discrete steps. The width of the each step is determined by
the receiver's instantaneous bandwidth. The instantaneous
bandwidth can be as small as a few hundred megahertz or
as large as many gigahertz. Whatever the instantaneous
bandwidth is, the total bandwidth that needs to be covered, divided by the instantaneous bandwidth, defines the
number of steps or scan states the ES system must be tuned
through. Usually the ES system has a tool that aids in developing a scan schedule that optimizes the probability of
intercept (POI) of the key threat radar systems expected
during the mission.
As the ES system scans the environment, radar signals
are detected (pulsed or continuous wave [CW]) and the parameters of the signals are measured. These measured parameters are then grouped by frequency, angle, pulse width
and/or a combination of these parameters. This is typically
called deinterleaving. After groups of these detections have
been collected, the ES system compares these common parameters with a database (sometimes known as a threat library) of radar system parameters. After this comparison,
if lucky, a unique radar identification will emerge. If not,
either a group of possible threats (ambiguities) or no identification (unknown emitter) results. Sometimes the ambiguities or the unknown detections resolve after multiple
detections (radar modes change, measurements get better
or more data aids in completing the threat identification).
After the identification or ambiguity group has been determined, the information becomes available on the aircrew's
cockpit displays.
This concept of operation for ES systems has served us
well for decades. However, new technology is changing how
threat radar systems operate. For example, radars are becoming more automatic with Active Electronically Scanned

39



JED - June 2015

Table of Contents for the Digital Edition of JED - June 2015

The View From Here
Conferences Calendar
Courses Calendar
From the President
The Monitor
World Report
Leadership Interview
Missile Warning for Fighter Aircraft
Technology Survey: RWR/ESM Systems
EW 101
2015 AOC Election Guide
AOC News
Index of Advertisers
JED Quick Look
JED - June 2015 - cover1
JED - June 2015 - cover2
JED - June 2015 - 3
JED - June 2015 - 4
JED - June 2015 - 5
JED - June 2015 - The View From Here
JED - June 2015 - 7
JED - June 2015 - Conferences Calendar
JED - June 2015 - 9
JED - June 2015 - Courses Calendar
JED - June 2015 - 11
JED - June 2015 - From the President
JED - June 2015 - 13
JED - June 2015 - 14
JED - June 2015 - The Monitor
JED - June 2015 - 16
JED - June 2015 - 17
JED - June 2015 - 18
JED - June 2015 - 19
JED - June 2015 - World Report
JED - June 2015 - 21
JED - June 2015 - Leadership Interview
JED - June 2015 - 23
JED - June 2015 - 24
JED - June 2015 - 25
JED - June 2015 - Missile Warning for Fighter Aircraft
JED - June 2015 - 27
JED - June 2015 - 28
JED - June 2015 - 29
JED - June 2015 - 30
JED - June 2015 - 31
JED - June 2015 - 32
JED - June 2015 - 33
JED - June 2015 - 34
JED - June 2015 - 35
JED - June 2015 - 36
JED - June 2015 - 37
JED - June 2015 - 38
JED - June 2015 - Technology Survey: RWR/ESM Systems
JED - June 2015 - 40
JED - June 2015 - 41
JED - June 2015 - 42
JED - June 2015 - 43
JED - June 2015 - 44
JED - June 2015 - 45
JED - June 2015 - 46
JED - June 2015 - 47
JED - June 2015 - EW 101
JED - June 2015 - 49
JED - June 2015 - 50
JED - June 2015 - 51
JED - June 2015 - 52
JED - June 2015 - 53
JED - June 2015 - 54
JED - June 2015 - 2015 AOC Election Guide
JED - June 2015 - 56
JED - June 2015 - 57
JED - June 2015 - 58
JED - June 2015 - 59
JED - June 2015 - 60
JED - June 2015 - AOC News
JED - June 2015 - 62
JED - June 2015 - 63
JED - June 2015 - 64
JED - June 2015 - Index of Advertisers
JED - June 2015 - JED Quick Look
JED - June 2015 - cover3
JED - June 2015 - cover4
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