What Is Multistatic Radar?

Multistatic radar is a radar configuration in which multiple spatially separated transmitters, receivers, or both operate together to detect, track, and locate targets. The IEEE Standard Radar Definitions characterize it as a system having two or more transmitting or receiving antennas separated by large distances relative to their sizes, so that each transmitter-receiver pair forms a distinct bistatic geometry. This geometric diversity allows multistatic networks to gather more information about a target than a single antenna pair can, including cross-section measurements from multiple aspect angles, which is particularly useful against targets with low radar cross sections. Multistatic radar draws from signal processing, estimation theory, and network communications, as well as classical radar theory.

The simplest non-trivial case is bistatic radar, with one transmitter and one receiver separated by a baseline. Multistatic systems generalize this to arbitrary numbers of nodes, enabling three-dimensional position estimation and, in some configurations, velocity ambiguity resolution that monostatic radar cannot achieve with a single antenna.

Geometry and Bistatic Measurement

Each transmitter-receiver pair in a multistatic network generates a bistatic range measurement: the sum of the range from transmitter to target and from target to receiver. This sum defines an ellipsoid with the transmitter and receiver as foci. With measurements from multiple pairs, the intersection of the corresponding ellipsoids constrains the target's position in three dimensions. Research on optimal geometry analysis for multistatic time-of-arrival localization has shown that the configuration of nodes relative to the target directly determines the Cramer-Rao lower bound on position error, with obtuse sensor arrangements generally yielding poorer localization accuracy than geometries that surround the target. The geometry also determines the bistatic radar cross section seen by each pair, since a target's reflectivity depends on the illumination and observation angles.

Passive and Active Multistatic Systems

Multistatic radar divides into active configurations, where the network includes its own transmitters, and passive configurations, where the receivers exploit signals of opportunity such as FM broadcasts, digital television, or navigation satellites. Passive systems offer the advantage of covert operation, since they emit nothing, and they can reuse licensed transmitters without coordination cost. Work on robust target localization for multistatic passive radar networks has addressed the challenge of positioning accuracy under measurement outliers and multipath interference, applying robust estimation algorithms derived from weighted least-squares and total least-squares frameworks. The receivers in these passive systems must first identify and time-stamp the direct-path signal from each transmitter before computing bistatic ranges.

Signal Processing and Detection

Processing the signals from multiple receivers introduces both opportunities and complications. When the receivers share a common clock or can synchronize phase coherently, the network can coherently combine waveforms from different perspectives to achieve spatial gains analogous to those of a phased array. Non-coherent combination, which uses amplitude or energy information rather than phase, is more practical when precise synchronization is unavailable and still provides diversity gain against target scintillation. Studies on multiple target detection and localization in UWB multistatic radars have explored the trade-offs between coherent and non-coherent fusion under realistic synchronization constraints, particularly for short-range through-wall and indoor sensing applications where wideband waveforms provide fine range resolution.

Applications

Multistatic radar has applications in a range of fields, including:

• Air and missile defense, where geometric diversity reduces the probability that a stealth target's shaping nullifies all bistatic cross sections
• Maritime surveillance, where spatially distributed receivers cover harbor approaches and littoral zones simultaneously
• Ground surveillance and through-wall sensing, where short-range UWB multistatic networks map human presence and motion
• Space situational awareness, where multiple ground stations contribute measurements to catalog resident space objects
• Automotive and infrastructure sensing, where networked short-range radars track pedestrians and vehicles from multiple angles