Gaining ELINT by intercepting and analyzing RF radar signals

In Electronic Warfare (EW), Electronic Intelligence (ELINT) systems provide military forces with critical insights into adversary Radar (Radio Detection and Ranging) operations by intercepting and analyzing Radio Frequency (RF) signals. These systems capture and decode the characteristics of Radar emissions, such as frequency, pulse patterns, and modulation types, allowing operators to identify the type and purpose of enemy Radar systems. By doing so, ELINT helps determine whether the Radar is being used for surveillance, targeting, or defense, which is essential for understanding enemy strategies, capabilities, vulnerabilities, and potential threats.

In this article, we will explore how ELINT receivers function, the underlying principles they rely on, and, most importantly, how they contribute to strategic decision-making and ensure our battlefield superiority.

Understanding the Basics of ELINT

At the core of ELINT operations is the task of detecting and collecting electromagnetic emissions, particularly from Radar systems. Radars play a crucial role in military operations by using radio waves to detect, track, and identify objects such as aircraft, ships, and missiles. They work by transmitting electromagnetic signals and then receiving the echoes that bounce back from objects in their path. The time delay and strength of these reflections provide information on the target's location, speed, and size.

Radars employed within military operations serve multiple purposes, from early warning systems that monitor distant airspace for potential threats to fire control Radars that guide weapons to their intended targets during the terminal phase. Understanding the characteristics and behavior of enemy Radars is critical for gaining insights into their operational capabilities and, potentially, their battlefield or defensive strategies. This is where ELINT systems come into play, allowing military forces to passively gather intelligence by intercepting these signals of interest without being detected or, in some cases, purposely being detected to observe targeting Radars in their normally hidden "wartime" mode.

Two critical concepts, the Radar range equation and the Probability of Intercept (POI), enable ELINT systems to intercept and analyze Radar emissions effectively.

Radar Range Equation

The Radar range equation is essential for understanding how far Radar and ELINT systems can detect signals of interest. For Radar, it calculates the maximum distance at which an object can be detected. For ELINT, it determines the range at which Radar signals can be intercepted. The key factors in this equation include the power transmitted by the Radar, the effectiveness (or gain) of both the Radar and receiver antennas, how well the target reflects Radar signals (Radar cross-section), and how much the signal weakens over distance (signal loss).

A simplified way to think of the Radar range equation is this:

Detection Range = (Transmitted Power × Antenna Gain × Target Reflectivity) ÷ Signal Loss

For example, let's say:

• The Radar transmits 1,000 watts of power.
• The antennas boost the signal by two times (gain of 2 for both the Radar and the receiver).
• The target reflects 10% of the signal (reflectivity of 0.1).
• The signal weakens over distance by a factor of 100 (signal loss of 100).

Plugging these values in, the detection range can be estimated as:

Detection Range = (1,000 × 2 × 2 × 0.1) ÷ 100 = 4

In this case, the Radar can detect a target at four times the base distance. If the base detection range is 5 kilometers, the Radar can detect the target at 20 kilometers.

ELINT systems use this same approach to determine how far away they must be to detect Radar signals without exposure.

Probability of Intercept (POI) 

POI refers to the likelihood of an ELINT receiver detecting a Radar signal within a given period of time. This depends on several factors, including how the Radar operates, the Radar's signal characteristics, and the capabilities of the ELINT system.

Here's how it works

When a Radar sweeps its beam across the sky, it does not emit energy continuously in all directions. Instead, it may focus the beam in specific sectors for short intervals. For example, suppose a Radar completes a full sweep every 10 seconds but only spends 1-second pointing in the direction of the ELINT system. In that case, the receiver has only a 10% chance of intercepting the signal at any given moment. This sweeping behavior means that the ELINT system must remain vigilant and continuously monitor the RF spectrum to improve its chances of intercepting the Radar signal.

Let's break it down with a basic example

Beam Dwell Time: If a Radar spends 1 second pointing in a given direction (dwell time) and the total time for a complete sweep is 10 seconds, the chance of being 'illuminated' by the Radar, which means the ELINT system is within the Radar's beam and can intercept the signal, is:

POI = Dwell Time ÷ Total Sweep Time = 1 second ÷ 10 seconds = 0.1 or 10%.

Radar Pulse Repetition Frequency (PRF): A Radar that emits pulses at a higher frequency (e.g., 1,000 pulses per second) has more chances to be intercepted. However, if the Radar only emits ten pulses per second, the ELINT system has fewer opportunities to detect those pulses during its scan. An ELINT receiver's ability to "catch" these pulses relies on how quickly and how often it scans the frequency band.

To improve POI, state-of-the-art ELINT receivers scan wide portions of the RF spectrum, and they do so with high sensitivity, ensuring that even brief or low-power emissions are captured. The goal is to reduce the time needed to detect a Radar signal, increasing the likelihood of intercepting signals from Radars that are trying to avoid detection by quickly sweeping or using low-power signals.

For example, if an ELINT system can scan an RF band in 0.5 seconds, it doubles the chance of intercepting a signal compared to a system that takes 1 second to scan the same range. This speed and sensitivity are vital on the battlefield, where adversaries might use techniques to minimize Radar exposure, such as reducing transmission times or lowering signal power.

By continuously improving these capabilities, ELINT systems maximize the POI, making it more difficult for enemy Radar systems to evade detection.

Figure 1: Table showing comparisons between the different RFeye Nodes.

A semi-recent example of ELINT in action comes from the 2003 Iraq War. ELINT systems played a significant role in targeting Iraq's Integrated Air Defense System (IADS). U.S. forces used ELINT to map out Iraqi Radar and missile defense networks prior to and during the initial stages of the war. Aircraft such as the RC-135V/W/U Rivet Joint/Combat Sent, equipped with advanced signal intelligence systems, intercepted and analyzed Radar emissions from Iraqi early warning and Surface-to-Air Missile (SAM) systems. This intelligence was crucial in planning and executing successful air operations, as it provided insights into the location and capabilities of enemy air defense systems.

By tracking Radar frequencies and operation patterns, U.S. forces could pinpoint the exact locations of SAM sites, such as the Soviet-era SA-2 and SA-6 systems. ELINT assets detected when Iraqi Radars "lit up" to engage coalition aircraft, often prompting quick responses with Radar-seeking missiles like the AGM-88 HARM, which targeted and neutralized these Radars before they could lock on to aircraft.

One specific tactic was faking airspace penetrations to provoke Iraqi Radar operators into activating their systems. This provided a clear map of Iraq's defensive Radar network, which ELINT systems exploited to Suppress Enemy Air Defenses (SEAD), making it safer for coalition airstrikes to proceed. The success of this ELINT-driven approach significantly diminished Iraq's ability to defend its airspace, leading to rapid air superiority for coalition forces.

How ELINT Helps Develop Countermeasures

ELINT is essential for developing Electronic Countermeasures (ECM) because it provides insight into enemy Radar systems, including their frequency, pulse patterns, and operational modes. With this information, ECM systems can jam Radar signals by overwhelming the Radar with noise or by deceiving it with false signals that confuse the system about a target's location or speed. Another crucial application of ELINT is in stealth technology, where it provides data on how enemy Radar systems detect objects. This intelligence helps engineers design aircraft with shapes and materials that reduce Radar reflection, effectively making the aircraft appear smaller or "invisible" to Radar, thus minimizing the chances of detection.

Furthermore, ELINT supports Anti-Radiation Missile (ARM) targeting, guiding weapons like the AGM-88 HARM to Radar sources based on their emissions. This intelligence helps ensure ECM systems stay effective even as adversaries improve their Radar systems, allowing friendly forces to maintain a tactical edge in the electromagnetic spectrum.

CRFS' tactical ELINT capabilities

CRFS provides military forces with adaptable ELINT solutions designed for rapid deployment in Areas of Operation (AOR) where radar and electronic threats are prevalent.

The RFeye SenS Remote monitors an ultra-wide frequency range all the way up to 18GHz or 40GHz, and will trigger on a pulse of interest to record high-fidelity IQ data in bands of 100MHz at a time – this IQ data is automatically indexed on-the-fly and stored in a database to allow instant search and retrieval. It is possible to focus the SenS Remote on specific frequency bands tied to regional threats, in order to narrow the search range. These lightweight receivers, ideal for Forward Operating Bases (FOBs) or remote locations, offer a tactical edge with the ability to reposition quickly and fill gaps as threats shift.

When paired with RFeye DeepView for real-time signal analysis and RFeye Site for precise geolocation, the system delivers actionable, mission-critical intelligence. This integrated solution allows operators to detect, analyze, and track hostile signals, ensuring forces maintain operational superiority. The decentralized nature of the system enables rapid setup and reconfiguration, making it highly effective for early warning, surveillance, and base defense.

CRFS's solution provides the flexibility needed in dynamic, high-threat environments, enhancing situational awareness, and assisting operators to neutralize emerging threats efficiently.

Conclusion

ELINT systems are a cornerstone within Electronic Warfare, offering military forces critical insights into the capabilities and behaviors of adversarial Radar systems. By intercepting and analyzing Radar emissions, ELINT helps identify Radar types, locate their positions, and understand their operational modes, allowing forces to anticipate and counter threats more effectively. As shown in the Iraq War, ELINT was instrumental in targeting and disabling Iraqi surface-to-air missile systems, securing air superiority.

Additionally, ELINT plays a vital role in developing countermeasures, such as jamming and deception techniques, as well as enabling stealth technologies and precision-guided weapons like anti-radiation missiles. This continuous feedback loop between intelligence gathering and countermeasure development ensures that military forces can adapt to and overcome even the most advanced Radar systems, maintaining a tactical edge in the electromagnetic spectrum.

ELINT remains a critical asset in ensuring battlefield superiority and advancing military operations in highly contested environments. Through its ability to provide real-time, actionable intelligence, ELINT ensures battlefield superiority and advances military operations.