Passive Radar
Passive radar for discreet air and coastal surveillance
Direct answer
Passive radar is best shortlisted as a discreet surveillance layer, not as a universal replacement for active radar. It uses a transmitter separate from the receiving sensor. A published Polish Academy trial used active air-traffic-control radar as the illumination source and detected and tracked airliners. The useful procurement question is therefore site-specific: can the proposed illuminators, geometry and integration path produce the warning time and track quality the mission needs?
Start with the surveillance job
Define the area, target set and warning time before discussing equipment. A port protecting an approach corridor, a border post watching low-level traffic and an air-defence unit supporting a national picture do not need the same output. State whether the passive layer is expected to discover tracks, maintain them, cue another sensor or contribute to a recognised air picture. That decision controls the required update rate, interfaces and acceptance test. It also prevents a silent receiver from being judged against a fire-control radar role it was not selected to perform.
Survey the site before fixing performance
Passive sensing depends on geometry. The buyer should require a survey of available illuminators, terrain masking, likely clutter, receiver siting, timing references and the communications path to the command system. The survey should identify how coverage changes when an illuminator is unavailable and which parts of the mission area need another sensor. A proposal can then state coverage for the surveyed configuration instead of repeating a general range figure. The same study should define spectrum coexistence, power, physical security and data backhaul at each receiver site.
Specify integration and acceptance
Ask what track format leaves the system, how tracks are correlated with existing radar or electro-optical sensors, and where identification takes place. Acceptance should use representative targets and routes across the surveyed geometry, with agreed measures for detection continuity, false tracks, latency and hand-off. Training must cover operators, maintainers and the analysts who tune the system to changing signal conditions. Sustainment should identify replaceable receiver elements, software support, calibration routines and the response time for faults. Confirm the proposed configuration, interfaces and export position before treating the layer as deployable.
Next action
Request a site-qualification briefing with the mission area, existing sensors and required command-system interface.
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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