See the air and coastal picture without ever giving your sensors away
Passive Radar
Overview
Passive radar that exploits LEO satellite illumination to detect and track without emitting: zero transmit power, no spectrum licensing, persistent coverage over hundreds of square kilometres from a single receiver site. Integrated into the wider air and coastal picture-compilation chain.
An emitter-free surveillance layer that detects and tracks aircraft and drones by exploiting signals already in the environment rather than transmitting its own, built for defence ministries, coast guards and critical-site owners who need persistent coverage that an adversary cannot locate, jam or tie to a single-power sensor ecosystem.
Key capabilities
- Zero transmit power: the sensor emits nothing, so there is no signature for anti-radiation missiles or electronic-intelligence receivers to home on.
- Exploits illuminators already in the environment rather than requiring an acquired emitter or spectrum licence to operate.
- Persistent, wide-area coverage from a single receiver site, watching continuously without advertising its position.
- Detects the targets that defeat traditional radar, including small drones, low-observable aircraft and slow-movers.
- Complements active radar rather than replacing it, holding the picture when emitting sensors must go silent to survive.
- Integrates into the buyer's own picture-compilation chain rather than a foreign integrated air-defence architecture.
- Deployable as a covert layer over borders, coastlines, restricted zones and critical sites under the buyer's own control.
Performance envelope
| Transmit signature | None, the sensor emits nothing |
| Detection range | Multiple range classes available |
| Illuminator sources | Configuration-dependent |
| Coverage geometry | Site-dependent, shaped by local transmitter geography and terrain |
| Target set | Includes small, low-observable and slow-moving contacts |
| Spectrum licensing | Not required to operate |
| Command-and-control interfaces | Integrated to existing systems on assessment |
| Environmental envelope | Available under controlled briefing |
| Detailed figures | Shared under briefing, not published |
Qualitative envelope only. Exact figures are configuration-dependent and shared under a controlled briefing against your requirement: never published.
In depth
Passive radar is not a transmitter but a receiver that listens for how existing signals in the environment reflect off targets. Because it emits nothing, there is no signature for an adversary to home on. The capability is assembled around the buyer's sites and terrain, and represented and sustained through one accountable team.
Illuminators of opportunity
The system exploits transmitters already present in the environment as its energy source, so it never radiates its own signal. Which sources are usable is shaped by the local transmitter geography and terrain around each site.
Receiver site
A passive receiver installation that collects the direct and reflected signals and extracts target tracks from them, delivering persistent wide-area coverage from a single, unobtrusive site.
Processing
The compute layer that correlates the reference and reflected signals, forms tracks, and classifies contacts, turning ambient energy into a usable surveillance picture rather than raw returns.
Command layer
A track picture presented to the operator and fed into the wider air and coastal picture, so passive radar augments existing surveillance rather than standing alone.
Operator
A human interprets and acts on the track picture. Doctrine, drills and training build crews who can exploit a covert layer and hand off to active sensors and effectors under pressure.
Integrations
Interfaces to the buyer's existing picture-compilation chain, air-defence and command-and-control systems, so the passive layer feeds and receives the common picture without a rip-and-replace.
Operational problems it addresses
- Maintaining air and coastal surveillance where an emitting radar would immediately be located and targeted by anti-radiation weapons or electronic attack.
- Detecting the small drones, low-observable aircraft and slow-movers that fly beneath the coverage of classical air-defence radar.
- Watching borders, coastlines and restricted zones persistently without advertising sensor positions to a hostile intelligence effort.
- Protecting critical national assets, including power, ports, government and military sites, with a covert layer that keeps working when active sensors must stay silent to survive.
- Adding a surveillance layer without acquiring spectrum, licensing an emitter or binding the picture into a foreign integrated air-defence architecture.
- Filling the coverage gaps active radars create the moment they shut down to avoid being found.
Deployment configurations
Why Unstrat: the difference
Unstrat is the authorised global representative and distributor for this capability. It is already in service with a track record behind it, so you are buying something that has done the job elsewhere, not funding a first attempt. You are not the test bed.
Versus a conventional emitting radar
An active radar announces itself the moment it transmits, making it a target for anti-radiation weapons and electronic attack. A passive sensor emits nothing, so it cannot be located, targeted or easily jammed. It keeps watching when an active sensor would have to go silent to survive.
Versus a major-power integrated air-defence architecture
Buying into a major-power sensor ecosystem ties the surveillance picture to a foreign architecture and its disclosure and integration conditions. This capability integrates into the buyer's own picture-compilation chain, keeping the air and coastal picture accountable to the buyer's flag.
Versus legacy air-defence radar not tuned for drones
Radars built for fast, high-flying aircraft are not optimised for small, slow, low-flying targets. Passive radar is deployed specifically to counter the contacts that defeat traditional radar: small drones, low-observable aircraft and slow-movers.
Versus adding another licensed emitter
A new active sensor means acquiring spectrum, licensing an emitter and adding another signature to defend. Exploiting illuminators already in the environment adds a surveillance layer without any of that, and without a spectrum licence to operate.
Versus a single-vendor closed sensor package
One-vendor packages lock a buyer into a fixed architecture. Deploying a passive layer that feeds and receives the existing common picture augments what a force already operates and keeps future options open.
How it reaches you
Sovereignty & localisation
- Buyer ownership of operational data and the track picture the system generates.
- Local control of system configuration and how the layer feeds the national picture.
- Options for local installation and integration of the receiver sites.
- In-region maintenance and sustainment rather than remote, supplier-gated support.
- Operator training and train-the-trainer programmes to build a sovereign crew base.
- Progressive technology transfer and component localisation, scoped per programme.
- A path towards independent sustainment so the capability outlasts the initial delivery.
Integration
- The buyer's existing air and coastal picture-compilation chain, so the passive layer feeds and receives the common picture.
- In-service air-defence and command-and-control systems, augmenting current coverage rather than replacing it.
- Active radar and other surveillance sensors, filling the gaps they leave when they must go silent.
- Effector and engagement-authority chains, keeping human decision-making in the loop.
- Mission and situational-awareness software already in use at the command post.
- National and site infrastructure, including power, siting and comms, assessed as part of configuration.
Procurement & delivery
- Because coverage is site-dependent, engagement begins with a coverage study of the specific sites, terrain and transmitter geography to be exploited.
- Export-control position and end-user-certificate chain are confirmed before any configuration is represented.
- Staged deployment, integration into the existing picture, contracting, delivery and acceptance testing follow the standard programme path.
- Operator training, warranty, spares and in-region sustainment are part of the same accountable engagement.
Passive Radar: questions
If it does not emit, how does passive radar detect anything?
It listens rather than transmits. The system exploits signals already present in the environment as its energy source and measures how they reflect off targets, forming tracks from that reflected energy. Because it never radiates its own signal, there is nothing for an adversary to locate, yet it still produces a usable surveillance picture.
Can an adversary locate or jam a passive sensor?
There is no transmit signature to home on, so anti-radiation weapons and electronic-intelligence receivers have nothing to find, and the sensor is far harder to jam than an emitting radar. That survivability is the central reason to deploy it alongside active sensors that must go silent to avoid being targeted.
Will it detect small drones and low-observable aircraft?
Countering exactly those targets is a core purpose. Small drones, low-observable aircraft and slow-movers are the contacts that defeat traditional air-defence radar, and passive radar is deployed as the covert layer tuned to see them.
Do we need a spectrum licence or a new emitter to operate it?
No. The system uses illuminators already in the environment rather than an acquired transmitter, so no spectrum licence is required to operate and there is no new emitter to defend or coordinate.
Does it replace our active radar?
No, it complements it. Passive radar fills the coverage gaps active sensors create when they must stay silent to survive, and integrates into your existing picture-compilation chain rather than standing alone or forcing a rip-and-replace.
What can you tell us about coverage and range figures?
Multiple range classes are available, but coverage is genuinely site-dependent. It is shaped by the local transmitter geography and terrain around each site. That is why procurement begins with a coverage study, and detailed figures are shared under a controlled briefing against your specific sites rather than published.
Who controls the picture and data once it is deployed?
The buyer. Options exist for ownership of operational data, local control of configuration and how the layer feeds the national picture, in-region maintenance, operator and train-the-trainer programmes, and progressive localisation, so the capability is operated and sustained under your own authority.
Why passive radar from an independent supplier rather than a major-power system?
A major-power sensor ties the surveillance picture into a foreign integrated air-defence architecture with its own disclosure and integration conditions. An independent, non-aligned origin integrates into your own picture-compilation chain and keeps the air and coastal picture accountable to your flag, through one team responsible from coverage study to sustainment.
Next step on this capability
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Applications it supports
Capability comparisons
Questions buyers ask
What is passive radar?
Passive radar finds and tracks aircraft by reading how signals already in the air reflect off them, rather than transmitting anything itself. Ours works from LEO satellite downlinks, broadcast television and cellular base stations at 0 W transmit power. Nothing radiates, so there is no signature for an anti-radiation missile or an ELINT receiver to home on, and no spectrum licence to apply for. It runs as a working layer inside air and coastal picture compilation, not as a laboratory demonstrator.
See: Passive radar: illuminators, targets and sitingPassive and active radar, side by side
Best passive radar system for drone detection
There is no single best one, because the answer turns on what illuminates your sky. Hensoldt Twinvis is well documented and publishes an instrumented range of 250 km working from FM, DAB and DVB-T transmitters. Ours exploits LEO satellite downlinks alongside broadcast television and cellular signals, covers hundreds of square kilometres from a single receiver site, and arrives without a member-state export chain behind it. Shortlist on illuminator availability over your own terrain first, then on whose ministry signs the licence.
Passive radar vs active radar: which should we buy?
Most credible air pictures use both. Active radar gives you engineered, predictable coverage, and it can be located and struck the moment it transmits. Passive radar gives up that control over geometry and gains survivability, because it emits nothing at all. We supply the passive layer specifically to hold the picture during the periods when your active sensors have to go quiet.
See: How the two sensing principles differ in practicePassive radar in the surveillance chain
What does a passive radar cost to own and run?
Three things drive the bill: power, sites and licensing. Hensoldt publishes average system power consumption of 2,500 W for Twinvis, and ERA's VERA-NG needs a central station plus three side receiving stations linked by microwave or fibre, which is a real civil-works and site-security cost. Ours covers hundreds of square kilometres from one receiver site with no transmitter, no rotating machinery and no spectrum fee. We do not publish a power figure and will not invent one, so ask for it in writing during evaluation.
See: Power, sites and licensing compared across the three systems
Passive radar for small-drone detection along a land border
This is one of the roles the system is built for. Small drones, low-RCS aircraft and slow-movers are exactly the target set that defeats classical air-defence radar, and they sit inside ours. Because the receiver transmits nothing, it can be sited along a border without telling the other side where your sensors are or inviting a strike on them. Coverage is site-dependent, so a border deployment starts with a study of the illuminators and terrain along the line.
See: Border and coastal roles for an emitter-free layerWhere passive sensing sits in a sovereign ISR architecture
Coastal surveillance radar that needs no spectrum licence
Passive radar needs no transmission licence because it has no transmitter. Hensoldt states the same position for Twinvis, so this is a property of the technique rather than a claim unique to us. What it buys a coast guard is the ability to put sensors on ground where an emitting radar would be politically, legally or tactically impossible. Ours feeds the coastal picture-compilation chain the customer already runs rather than replacing it.
Alternative to Hensoldt Twinvis for a state outside NATO
Functionally, ours is the close match: it detects non-emitting targets from illuminators already in the environment, transmits nothing and needs no spectrum licence. Twinvis publishes range and accuracy figures that we do not, and an honest evaluation should put both systems in a trial over your own terrain instead of comparing brochures. The procurement difference is plain enough. No German, American or Chinese authority sits between you and the next software release or the next spare receiver.
Can passive radar detect low-RCS and stealth aircraft?
Low-observable and low-RCS aircraft are inside our published target set, alongside small drones and slow-movers, because the technique reads reflected ambient energy rather than a returned pulse from your own transmitter. Hensoldt makes a similar claim for Twinvis in its datasheet. We do not publish detection ranges against specific target classes, so treat any vendor's stealth claim, ours included, as something to be measured in a trial rather than accepted from a page.
See: Target set and detection principleDetection-principle rows for all three systems
How many receiver sites does one passive radar system need?
One. That matters more than it sounds, because siting is where passive-radar programmes get expensive. Hensoldt runs one sensor per site with clustering up to five where more coverage or accuracy is wanted, and ERA's VERA-NG needs four sited and linked stations for a single system. Four pieces of secured real estate, four power feeds and the links between them is a different project from one.
Under emission control our air-defence radars have to stay silent, and we lose the picture exactly when we need it. What layer keeps working?
That gap is the reason emitter-free sensing exists. A passive receiver has nothing to switch off, so it keeps compiling tracks while the active sensors are dark and cannot be located, targeted or jammed in the usual way. We supply it as a layer inside your existing air and coastal picture chain rather than as a replacement air-defence radar, which keeps the doctrine you already train to. Crews still need to be drilled on handing contacts back to active sensors and effectors under pressure.
See: Covert coverage when active sensors go quietThe emitter-free layer in the wider surveillance picture
What should a defence ministry buy to watch a long land border for small drones without revealing where its sensors are?
Start with a coverage study, because passive radar performance is shaped by local transmitter geography and terrain, and a border of several hundred kilometres will not be uniform. From there the pattern is staged receiver sites feeding the national picture, each covering hundreds of square kilometres and emitting nothing. Pair it with the counter-drone layer so a detection becomes a decision rather than a log entry. We carry that chain from the first study through installation and in-region sustainment with one team.
See: Layered counter-drone detection and defeatPassive radar deployment roles
We cannot rely on German or American export approval for a sensor programme. Who supplies passive radar without a member-state licensing chain?
Both Twinvis and VERA-NG come through an EU and NATO member-state export chain, which is documented and legitimate and also permanent. The first approval is the visible part. Every later software release, spare receiver and coverage extension goes back through the same foreign capital, which may hold a different view of your region by then. Our origin is non-aligned, the sustainment team is in region, and no third government holds a standing right to review what you do with the picture you compile.
Does passive radar still work over desert or open water, where there are very few broadcast transmitters?
This is the right question to ask any passive-radar vendor, and it separates them quickly. Twinvis exploits FM, DAB and DVB-T at sensor-to-transmitter distances from a few kilometres to more than 100 km, which suits a densely broadcast landmass. Over desert, open sea or a thinly populated district that transmitter map thins and the geometry thins with it. Ours adds LEO satellite downlinks to the broadcast and cellular sources, and satellite illumination does not stop at the edge of the terrestrial network.
What is the difference between a passive ESM tracker such as VERA-NG and a passive radar, and do we need both?
They solve different problems and are not substitutes. An ESM tracker localises what the target itself radiates, which ERA does to 400 km with 0.01 degree azimuth accuracy and at least 200 real-time tracks, and the ELINT product that comes with it has no equivalent in a passive radar. Against a quiet quadcopter it has nothing to work with. Passive radar reads the reflection instead, which is why drones and low-RCS aircraft are in our target set. Several air forces run both layers for precisely that reason.
See: Why an ESM tracker and a passive radar are not the same buy
Who installs the receiver and keeps it running once the delivery contract closes?
The same team that supplies it, working in your region. Our passive radar is a fielded surveillance layer rather than a research demonstrator, and it is installed and sustained in region rather than shipped from a distant depot. Procurement runs from a coverage study through staged deployment and integration into your existing air and coastal picture, with one accountable channel across the whole engagement. Nothing in the update path needs a third country's signature.
See: How an installation and sustainment engagement is structuredSensing that stays accountable to your flag