HENSOLDT TwInvis: The Passive Radar That Can See Stealth Aircraft Without Emitting a Signal
TwInvis — “twin invisible” — is HENSOLDT’s passive, multi-static radar system that detects and tracks air targets by exploiting ambient FM radio and DVB-T television broadcasts rather than emitting any signal of its own. It is one of the first commercially available passive coherent location (PCL) systems globally.
The Logic of Passive Radar
Where an active radar illuminates and listens for its own reflections, TwInvis opportunistically borrows signals from multiple FM stations and DVB-T transmitters as reference sources. A multi-static geometry — using many non-collocated transmitter-receiver pairs — enables cross-correlation triangulation with high position accuracy. Proprietary signal processing algorithms separate weak target reflections from the noise floor and ground clutter.
The Stealth Argument
Stealth aircraft optimize their radar cross-section reduction at X and L-band frequencies used by conventional military radars. FM broadcasts operate in VHF (87.5–108 MHz) — far lower frequencies with much longer wavelengths. At VHF, shaping-based stealth is less effective, making TwInvis theoretically capable of detecting platforms like the F-35 that would be near-invisible to conventional radars. This claim is supported by published research, though classified testing details remain undisclosed.
Technical Parameters
- Signal sources: FM radio (87.5–108 MHz VHF), DVB-T TV (174–790 MHz VHF/UHF)
- Emissions: zero — fully passive
- Detection range: ~100–150 km for large targets using FM sources
- Platform: fixed or mobile containerized
Sources
hensoldt.net · IEEE Aerospace Conference · Jane’s Radar and Electronic Warfare Systems
