What exactly is the Low Probability of Intercept Radar (LPI)?

Low Probability of Intercept
Turkish Company Aselsan's ALPER LPI Radar (Source: Aselsan)

In today’s naval battlefield, most of the radars, as in surveillance, reconnaissance, and target tracking radars, have to cope with very capable and advanced threats designed to contribute to the degradation of radar performance. Electronic warfare support (ES) interception capabilities, electronic attack (EA) systems, radar warning receivers (RWRs), and antiradiation missiles (ARMs) are examples of such threats.

To see and not to be seen

To work efficiently among these measures and accomplish the missions, radars have to hide their emissions from hostile receivers. For this purpose, radars use power management, wide operational bandwidth, frequency agility, antenna sidelobe reduction, and advanced scan patterns (modulations) to mask their presence. These radars are called Low Probability of Intercept (LPI) radars and use techniques “to see and not to be seen” by modern and capable intercept receivers.

Tracking an opponent without alerting

Modern LPI radars with low power and high bandwidth have become difficult to detect and parameterize by conventional electronic warfare devices. LPI is that property of an emitter that, because of its low power, wide bandwidth, frequency variability, or other design attributes, makes it difficult to be detected or identified utilizing passive intercept devices such as radar warning, electronic support, and electronic intelligence receivers while it is searching for a target or engaged in target tracking. This feature is desirable in radar because it allows finding and tracking an opponent without alerting them to the radar’s presence. This also protects the radar installation from anti- ARM.

In the past, many types of radar were designed to transmit short-duration pulses having relatively high peak power, to reduce all the propagation losses of the electromagnetic waves, and, at the same time, to guarantee a straightforward recovery of the reflected wave from the target in clutter. LPI signals can be realized using wide operational bandwidth, frequency agility, proper power management, antenna sidelobe reduction, and advanced scan patterns.

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LPI detection range comparison

In particular, reducing the radar’s peak adequate radiated power (ERP) using some form of pulse compression techniques is a commonly used approach to realize LPI radar signals. Pulse compression based on intrapulse modulation is very effective in practice, leading to a sizeable time-bandwidth product and high radar signal processing. Besides, optimization techniques have been exploited and developed recently to design radar waveforms that can increase the performance of LPI radar systems. LPI waveforms include Frequency Modulation Continuous Wave (FMCW), several polyphase-coded CW waveforms such as Frank, P1, P2, P3, and P4, frequency hopping, and combined frequency hopping-phase coding.

Reduced probability of Intercept

LPI radar systems aim to reduce the probability that an EW receiver can detect a threat signal in two ways. First, by carefully managing when and where power is transmitted through its radiation and scan patterns. Second, the radar waveform aims to reduce the average power density by using high duty cycles or continuous wave signals with advanced modulation techniques that cover wide bandwidths. LPI radars work to detect targets at a more extended range than an intercept receiver.

This concept is well-summarized in a statement, “It tries to see and not be seen.” This response to the increasing capability of modern intercept receivers to detect and locate radar emitters, possibly leading rapidly to an electronic attack or the physical destruction of the radar by guided munitions or ARM.

low probability of intercept radar
LPI-2000 radar of GEM Elettronica


On the naval battlefield, situational awareness and threat evaluation are achieved using tactical surveillance radars to detect and track targets. For covert operations, detection and tracking of targets should be as quiet as possible. These systems should employ LPI technology to decrease the probability of passive detection by hostile forces.

LPI is considered an essential tactical requirement and is being specified by much military personnel using radar today. LPI radar has specific design features that render it difficult to detect. LPI is the property of an emitter that, because of its low power, wide bandwidth, frequency variability, or other design attributes, makes it difficult to be detected or identified utilizing passive intercept receiver devices. LPI radars attempt to detect targets at longer ranges than intercept receivers to detect the radar. Thus, the objective of an LPI radar is “To See and Not Be Seen,” or “To Detect and Not Be Detected.” As a result, the usage of LPI radars under tight “EMCON” conditions will provide an advantage in establishing a recognized maritime picture to the user side.

Check out Naval Library App to find out the specifications of LPI radars.

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