Passive Radar Systems and Signal Processing Techniques

Passive radar systems harness pre-existing electromagnetic emissions to detect and track objects without the need for dedicated transmitters. By exploiting so-called illuminators of opportunity such as broadcasting networks, satellite navigation signals and telecommunications infrastructure, these systems offer covert, cost-effective and low-interference alternatives to conventional active radar. Fundamental to their operation is the receiver’s ability to correlate a reference signal—collected directly from the illuminator—and the surveillance signal—reflections from targets. Signal processing techniques range from matched filtering and range-Doppler processing to advanced time-frequency analysis, coherent and non-coherent integration, and synthetic aperture imaging. Recent advances have focused on multistatic and bistatic configurations enabling enhanced spatial resolution, robust clutter suppression and track-before-detect strategies for low-observable or manoeuvring targets. Emerging applications span maritime surveillance, automotive sensing, airborne and spaceborne platforms, and unmanned aerial vehicle detection. The global significance of these systems lies in their passive nature, resilience to electronic countermeasures, and adaptability to diverse operational environments.

Research from Nature Portfolio

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Research from all publishers

One study has demonstrated high-quality imaging of maritime vessels using signals from multiple global navigation satellites in a passive multistatic synthetic aperture radar configuration. A two-stage processing chain first detects moving ships via long-time integration and then exploits Doppler history analysis with short-time Fourier transforms combined with robust velocity estimation. The approach yields focused bistatic images which are fused across satellites, delivering enhanced resolution in real experimental trials.

Another development addresses forward-looking passive radar for automotive safety, employing a non-uniform linear array of receive antennas and Doppler beam sharpening to localise stationary and moving scatterers using terrestrial and satellite illuminators. A novel ambiguity removal algorithm adapts digital beam patterns to suppress mirror echoes and is further refined with apodisation to manage noise. Simulation results indicate reliable scene mapping over wide angular sectors with minimal hardware complexity.

In the domain of cellular networks, researchers have proposed a 5G-based passive coherent location system that leverages the periodic synchronisation signal block of fifth-generation networks as the sole illumination source. The processing pipeline adapts classic pulse radar methods, addressing velocity ambiguity in single-target scenarios and demonstrating target detection under sparse transmission conditions. Validation with real-world 5G data confirms the feasibility of short-range passive radar deployment within existing mobile infrastructure.

Passive Radar Systems and Signal Processing Techniques publication trend

The graph below shows the total number of articles in passive radar systems and signal processing techniques across all publications each year (not limited to Nature Index journals).

Technical terms

Passive radar: A radar system that uses non-cooperative external transmissions rather than dedicated transmitters.

Illuminator of opportunity: Any pre-existing source of electromagnetic radiation exploited for passive sensing.

Bistatic geometry: A configuration in which transmitter and receiver are spatially separated.

Coherent integration: Summation of phase-aligned signal returns to improve signal-to-noise ratio.

Non-coherent integration: Summation of signal magnitudes or powers without phase alignment.

Doppler beam sharpening: A signal processing technique leveraging Doppler shifts to enhance angular resolution.

Synthetic aperture radar (SAR): A method that synthesises a large antenna aperture by combining data over time to achieve high-resolution imaging.

References

1. Maritime Ship Target Imaging With GNSS-Based Passive Multistatic Radar. IEEE Transactions on Geoscience and Remote Sensing (2023).
2. Forward-Looking Passive Radar With Non-Uniform Linear Array for Automotive Applications. IEEE Transactions on Vehicular Technology (2023).
3. SSB-Based Signal Processing for Passive Radar Using a 5G Network. IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing (2023).