Guest Editorial: Multistatics and passive radar

Welcome to the special issue of ‘Multistatic and Passive Radar’. The motivation for this special issue stems from the long running, biennial, Multistatics and Passive Radar Focus Days organised and hosted by Fraunhofer FHR in Wachtberg, Germany. This exciting collection brings together cutting-edge research in multistatic radar, passive radar, and related topics from the 2023 Focus Days. Multistatic radar systems employ multiple transmitters and/or receivers, which offer several advantages over traditional monostatic radars. These include wide area surveillance, improved accuracy, and enhanced resistance to jamming and spoofing attacks.

The need for advanced radar has increased in recent years due to the proliferation of modern threats, such as stealth aircraft, missiles and small drones. Passive radars provide an attractive complement to monostatic systems in that they utilise signals emitted by pre-existing, often communications, transmitter infrastructure. The spatial separation between transmitter and receiver/s offers a high degree of sensor-sanctuary for the passive radar receiver. In addition, passive radars do not increase EM spectrum congestion. They have gained considerable attention in recent years due to their potential for varied defence and security applications.

This special issue aims to highlight the latest advances, challenges, and opportunities in multistatic and passive radar systems. By bringing together leading experts from academia and industry, we hope to provide valuable insights into current research trends and future directions for these important fields of study. We hope that this special issue serves as a valuable resource for researchers, engineers, and practitioners working in the field of radar technology, inspiring new ideas and collaboration among them.

In this Special Issue you will find papers, all of which underwent peer review, that cover different topics linked to multistatic and passive radar.

The accepted papers may be clustered into four main categories, namely employing emerging communications systems for new multistatic setups, synchronisation between spatially distributed nodes, tracking, and answer the question of how best to present bistatic/multistatic results to the end-user. The papers which falls into the first category deals with new communications waveforms and show in theory and practical applications the achieved results. The papers that constitute the first category are from Guenin et al. and Maksymiuk et al. The second category of papers investigates the problem of exchanging time information among the netted nodes in a multistatic setup. These papers are from Valdes et al. and Busley et al. The third category of papers deals with the problem to correct labelling of targets and tracking them in a multistatic constellation. These papers are from Penggang et al., two contributions from Guan et al, and one from Tang et al. The fourth category proposes a new method for displaying radar results in a 3D polar plot. The paper in this category is a contribution from Miao et al. A synopsis of each of the papers in this special issue follows.

Maksymiuk et al. propose a passive automotive radar based on 5G communication signals as an alternative to active radars to provide situational awareness. Their approach shows the possibility of commensal utilisation of the new telecommunication standard for automotive radar applications.

Guenin et al. present in their paper a single-antenna receiver passive radar system leveraging the 4G/5G long-term evolution network as an illumination source for moving target detection, such as trains, car, planes and unmanned aerial vehicles.

Valdes et al. propose and characterise a synchronisation system for moving platforms employing a wireless two way link between them. The findings show that the investigated combination of hardware and software is suitable for radar applications operating in the L-, S- and C-bands.

Busley et al. present a method to passively synchronise data records via global navigation satellite systems (GNSS) raw signals requiring only a GNSS antenna, an analogue-to-digital converter and some additional computation hardware. Correlation of individual signals from the GPS, Galileo and BeiDou constellation enables sub-nanosecond time precision.

Penggang et al. propose a track initialisation algorithm using Neutrosophic Hough transformations to improve accuracy and computational speed for a multiple-flight trajectories within a multistatic scenario.

The first paper from Guan et al. (Dual-labelled…) propose a solution for associating emitters with measurements for multi-target tracking within a complex electromagnetic environment by employing generative adversarial networks to extract and classify the signals.

In the second paper by Guan et al. (Distributed multi-target tracking…) presents a multi-target tracking fusion algorithm based on consensus arithmetic averaging to address the limitations of sensor detection field of view and information fusion difficulty when tracking multiple targets in a distributed Airborne passive bistatic radar network.

The paper of Tang et al. proposes a multi-target track-before-detect scheme for a passive radar system based on signals emitted by Global Navigation Satellite Systems.

Miao et al. explore a method to describe the three-dimensional echo data model in such a manner that programmable pipeline of GPU can perform well to display any radar result in a 2D and 3D Plan Position Indicator shader.

All of the papers selected for this Special Issue show that the field of Multistatic and Passive Radar is steadily moving forward. With contributions from leading experts in the field, it provides a comprehensive overview of the current state-of-the-art research. The articles cover topics, such as signal processing methods for multistatic systems, array signal processing for passive radars, and detection algorithms for target classification.

While significant progress has been made in recent years, there remains much work to be done in this area. This special issue serves as a valuable resource for researchers, students, and practitioners looking to stay up-to-date on the latest developments in multistatic and passive radar technology. It also provides inspiration for those seeking to explore new directions in this rapidly evolving field.

Matthias Weiss: Conceptualization; writing—original draft. Diego Cristallini: Writing—review and editing. Daniel O'Hagan: Writing—review and editing.