28-09-2012, 12:15 PM
Radar And ESM: The Current State Of The LPI Battle
[attachment=34686]
Abstract
This paper discusses the current and projected future capabilities of “Low Probability of
Intercept” radars and of the intercept receivers used by Electronic Support Measures (ESM)
systems. In discussing the possible future sensitivity of the latter it makes use of the Matched
Incoherent Receiver to show how the intercept ranges may be able to increase in the future.
It then discusses future radar tactics which can make interception harder, and concludes that
there is no overwhelming advantage to one side or the other, but the balance will depend on
the particular tactical situation.
Introduction
The “classic” situation between radar and
ESM (intercept receivers) has been that the
intercept receiver has no difficulty
detecting the radar, and even sometimes its
sidelobes, at long ranges. This is because
the radar must transmit enough power for
the signals to be detectable even after
reflection at the target, whereas the
propagation between radar and ESM is only
one-way.
More recently, however, the increased
signal processing gain obtainable from a
radar. which is often expressed in terms of
the time-bandwidth product of the signals
being processed, has given the radar the
potential ability to alter that balance, on the
assumption that the intercept receiver
cannot duplicate the radar's processing gain.
Interception and Exploitation
Another measure of the difficulty of
intercepting or identifying the radar power
it transmits, since conventional intercept
receivers are generally sensitive to the peak
power in the signal, whereas the radar,
using a matched filter, is sensitive to mean
power. “Low Probability of Intercept” is
the usual term to describe radars which
pose difficulties to an ESM system because
of the weak signal levels which it presents
to the receiver, and generally refers to
signals which are difficult to detect above
the ESM receiver's threshold. A more
operationally-meaningful measure is the
ability of the intercept receiver to react to
the detection of the emitter.
Intercept Ranges
Although a variety of radars exist with low
peak power levels, and some have wellestablished
LPI/LPE characteristics, the
radar family which has made the greatest
play of its LPI/LPE capability is
PILOT/SCOUT (Ås (2)). A good place to
start the analysis of the issues is with a
baseline performance of this radar against a
typical late-1980's IFM-based ESM. The
following tables, which are also given in
reference (1), indicate how the range at
which the radar can detect its target and at
which it can be detected, in free space
Receiver Developments
It is interesting to note that whilst PILOT
has been in service for about 15 years, the
raw sensitivity of ESMs is only at the level
which was considered to be the “state of the
art” in development when the radar was
introduced, so the radar's LPI has proved,
form the radar designer's point of view, to
be encouragingly robust' over a reasonable
time period. The rate of development of
both radar and ESM systems has proved to
be significantly slower than might have
been expected 15 years ago. This has been
in part a consequence of the end of the cold
war which removed the most electronicallysophisticated
“threats” and in part an
example of the general slowing-down of
advances in electronics as the field matures.
Noise Waveforms
There is a commonly-held belief that LPI
radars will, in future, have to transmit more
noise-like waveforms than have commonly
been used in the past, in order to avoid
being intercepted, but the arguments above
about the precision with which even a
deterministic waveform would have to e be
estimated in order to be integrated
coherently, combined with the gain which
can be achieved with incoherent integration,
together with the practical difficulty of
implementing more noise-like waveforms
may significantly reduce the attractiveness
of this idea.
Conclusion
An earlier paper (Fuller (4)) compared the
battle between radar and ESM to the Trojan
war. A more appropriate analogy now
might be a game of chess, in which each
side has the same number of pieces, but the
victory will go to the player who uses skill
and intelligence to make the best tactical
and strategic use of the assets at his
disposal. Or to revert to the image of the
Trojan war, Wily Odysseus in the end was
more effective than the Wrath of Achilles.
[attachment=34686]
Abstract
This paper discusses the current and projected future capabilities of “Low Probability of
Intercept” radars and of the intercept receivers used by Electronic Support Measures (ESM)
systems. In discussing the possible future sensitivity of the latter it makes use of the Matched
Incoherent Receiver to show how the intercept ranges may be able to increase in the future.
It then discusses future radar tactics which can make interception harder, and concludes that
there is no overwhelming advantage to one side or the other, but the balance will depend on
the particular tactical situation.
Introduction
The “classic” situation between radar and
ESM (intercept receivers) has been that the
intercept receiver has no difficulty
detecting the radar, and even sometimes its
sidelobes, at long ranges. This is because
the radar must transmit enough power for
the signals to be detectable even after
reflection at the target, whereas the
propagation between radar and ESM is only
one-way.
More recently, however, the increased
signal processing gain obtainable from a
radar. which is often expressed in terms of
the time-bandwidth product of the signals
being processed, has given the radar the
potential ability to alter that balance, on the
assumption that the intercept receiver
cannot duplicate the radar's processing gain.
Interception and Exploitation
Another measure of the difficulty of
intercepting or identifying the radar power
it transmits, since conventional intercept
receivers are generally sensitive to the peak
power in the signal, whereas the radar,
using a matched filter, is sensitive to mean
power. “Low Probability of Intercept” is
the usual term to describe radars which
pose difficulties to an ESM system because
of the weak signal levels which it presents
to the receiver, and generally refers to
signals which are difficult to detect above
the ESM receiver's threshold. A more
operationally-meaningful measure is the
ability of the intercept receiver to react to
the detection of the emitter.
Intercept Ranges
Although a variety of radars exist with low
peak power levels, and some have wellestablished
LPI/LPE characteristics, the
radar family which has made the greatest
play of its LPI/LPE capability is
PILOT/SCOUT (Ås (2)). A good place to
start the analysis of the issues is with a
baseline performance of this radar against a
typical late-1980's IFM-based ESM. The
following tables, which are also given in
reference (1), indicate how the range at
which the radar can detect its target and at
which it can be detected, in free space
Receiver Developments
It is interesting to note that whilst PILOT
has been in service for about 15 years, the
raw sensitivity of ESMs is only at the level
which was considered to be the “state of the
art” in development when the radar was
introduced, so the radar's LPI has proved,
form the radar designer's point of view, to
be encouragingly robust' over a reasonable
time period. The rate of development of
both radar and ESM systems has proved to
be significantly slower than might have
been expected 15 years ago. This has been
in part a consequence of the end of the cold
war which removed the most electronicallysophisticated
“threats” and in part an
example of the general slowing-down of
advances in electronics as the field matures.
Noise Waveforms
There is a commonly-held belief that LPI
radars will, in future, have to transmit more
noise-like waveforms than have commonly
been used in the past, in order to avoid
being intercepted, but the arguments above
about the precision with which even a
deterministic waveform would have to e be
estimated in order to be integrated
coherently, combined with the gain which
can be achieved with incoherent integration,
together with the practical difficulty of
implementing more noise-like waveforms
may significantly reduce the attractiveness
of this idea.
Conclusion
An earlier paper (Fuller (4)) compared the
battle between radar and ESM to the Trojan
war. A more appropriate analogy now
might be a game of chess, in which each
side has the same number of pieces, but the
victory will go to the player who uses skill
and intelligence to make the best tactical
and strategic use of the assets at his
disposal. Or to revert to the image of the
Trojan war, Wily Odysseus in the end was
more effective than the Wrath of Achilles.