Passive radar — also called passive coherent location (PCL) or passive bistatic radar (PBR) — is the discipline of detecting and tracking moving targets without emitting a single watt of your own RF energy. Instead of an active transmitter, the system listens for energy from a third-party illuminator of opportunity already lighting up the sky and uses the target’s reflected echoes to triangulate its position, velocity and trajectory in space and time. The illuminator can be almost anything that radiates persistently and broadly: FM broadcast transmitters at 88–108 MHz, with 50–100 kW EIRPs delivering hundreds of kilometres of coverage; DVB-T digital television multiplexes whose wideband OFDM structure gives excellent range resolution; DAB+ digital radio in Band III; GSM, LTE and 5G cellular base stations whose dense urban geometries make them ideal for low-altitude and counter-UAS work; Wi-Fi access points for short-range indoor passive radar; HF broadcast transmitters and NDBs (non-directional beacons in the 190–530 kHz band) for surface-wave, low-altitude, beyond-line-of-sight detection; and increasingly Starlink and other LEO downlinks, whose dense orbital geometries are opening coverage in oceanic, polar and remote terrain where terrestrial broadcasters are absent. The technique was theoretically proposed in the 1930s but became operationally tractable only when wideband software-defined receivers, multi-channel coherent SDR front-ends, and FPGA/GPU cross-correlation engines arrived in the 2000s.
Adelaide is at the centre of Australia’s sovereign passive radar capability. DST Group at RAAF Edinburgh has driven passive radar research for more than fifteen years, and two Adelaide-rooted companies have turned that research into fielded systems. Daronmont Technologies developed the ‘Stealth’ passive coherent location system through a decade-long partnership with DST Group at RAAF Edinburgh, winning Australian Department of Defence tenders and becoming the first Australian passive radar system delivered to the United States Government. Silentium Defence, also Adelaide-built, produces MAVERICK for terrestrial air-target tracking and Oculus for resident-space-object cataloguing, and delivered the first sensors for Australia’s $7.7 billion AIR6500 Joint Air Battle Management System ahead of schedule in 2024 — both companies co-designated under the 2026 National Defence Strategy as Sovereign Industrial Capability Priorities. International peers in the fielded-system space include Hensoldt Twinvis (Germany), Lockheed Martin Silent Sentry, and Thales’s multi-static primary surveillance radar work with Roke Manor and NATS in the United Kingdom. On the research frontier, Germany’s Fraunhofer Institute for High Frequency Physics and Radar Techniques (FHR) demonstrated SABBIA 2.0 in 2024 — a passive radar using Starlink downlinks as the illuminator, operable from a moving ship platform — while France’s ONERA DEMR has published extensively on DVB-T based detection of micro-UAVs and maintains one of Europe’s strongest bistatic radar research programmes. Strong academic systems come from Warsaw University of Technology (PaRaDe) and Sapienza University of Rome. At the open-source and hobbyist end of the spectrum, GNU Radio passive-radar flowgraphs exist for FM and DVB-T, the KrakenSDR five-channel coherent receiver platform supports passive-radar geolocation alongside direction-finding, and the RTL-SDR community has demonstrated working passive radar against airliners using two $30 dongles and a kitchen-table reference antenna — capabilities thought to be government-laboratory-only fifteen years ago.
The strategic appeal is unmistakable: passive radar is silent (a target’s radar warning receiver sees nothing because nothing is being radiated by the sensor); covert (the receiver site is invisible until you find a small antenna farm); low-cost compared with active phased-array radar; spectrum-friendly (it consumes no allocation of its own); and persistent (commercial illuminators run 24/7 with no maintenance crew of yours). The technical challenges are real — direct-path interference cancellation, reference-channel separation, ambiguity-function processing across long coherent integration times, bistatic geometry mathematics, multipath rejection, and the sheer compute cost of correlating multi-megasample-per-second IQ streams — and these are exactly the kind of problems that fall naturally into this conference’s territory. The shift toward LEO satellite illuminators adds further dimensions: Doppler geometry differs markedly from terrestrial bistatics, satellite orbital mechanics must be tracked in real time, and the downlink waveform structure of constellations like Starlink presents new cross-ambiguity function design challenges that are only beginning to be characterised in the open literature.
Applications cover the full breadth of the audience: covert air defence and border-incursion monitoring for the Defence community; counter-UAS detection at low altitudes where conventional radar has coverage gaps; maritime surveillance of small surface craft using HF surface-wave illuminators; resident-space-object tracking and space domain awareness using both terrestrial and orbital illuminators; atmospheric and ionospheric science through bistatic Doppler observations; and a genuinely open research playground for university groups, amateur experimenters and indie defence-tech outfits alike. We particularly welcome papers, demonstrations and panel contributions on passive-radar systems at every scale — from sovereign-capability fielded platforms down to two-RTL-SDR student projects — at SDR Conference 2026.