PARIS — German sensor specialist Hensoldt expects to sell a small number of its Twinvis passive radar kits to the country’s air force, a move that would thrust the service into a growing and still-secretive technology field.

Details of the deal remain to be finalized, but company spokesman Joachim Schranzhofer confirmed to Defense News that the Ministry of Defense had signaled an interest to buy. Funds likely would come through a generic line item for air surveillance technology that’s tucked away in a priority list for Germany’s newfound defense-spending appetite.

A spokesperson for the Ministry of Defense in Berlin did not return repeated requests for comment.

Passive radar can detect aerial objects – including planes optimized for stealth, like the F-35 – by studying their echoes in the wave salad of civilian radio and television broadcast transmitters. The technology emits no signal itself, which means opponents are unaware they are being tracked, and from where.

Passive radar is useless in undeveloped and remote regions where there are too few signals from which to read disturbances in the electromagnetic field.

But Hensoldt has claimed for years that advances in computing power have improved the technology, enabling almost targeting-quality tracks from even the faintest signals.

The company recently began positioning Twinvis as a new component for ground-based air defense scenarios. Passive radar could augment active sensors for more accurate targeting of incoming threats, for example. It could also lead to limiting use of active radar, a dangerous proposition that gives away the defender’s location and capabilities, according to conventional wisdom.

Earlier this year, Hensoldt and Diehl Defence announced the companies had teamed to integrate Twinvis into Diehl’s IRIS-T range of missile-defense systems as an optional component. A sale to Egypt of 16 IRIS-T units — cleared last year during the final days of the Merkel government — is slated to include the passive radar option and would make Cairo one of the first users of the technology.

Switzerland, which experimented with passive radar during its Air 2030 air-defense modernization campaign, is thought to be another customer.

However, a promised German delivery of an IRIS-T unit to Ukraine for shielding Kyiv is unlikely to include a passive radar option, as the country offers insufficiently dense coverage coverage from radio-frequency transmitters, according to issue experts.

Russia has destroyed many TV and radio towers since it began its bloody assault on Ukraine in late February.

The German air force has toyed with the Twinvis passive radar for several years, though officials have so far shied away from buying it. Defense News reported in 2019 that the service had set up a preliminary acquisition track after sponsoring a large-scale air traffic surveillance demo over Bavaria in late 2018.

The company dispatched a team of passive radar engineers to a pony farm near Berlin’s Schönefeld airport to catch two U.S. F-35 stealth planes visiting for the 2018 Berlin Air Show as they were leaving the exhibit, Defense News reported in 2019. The equine excursion helped analysts compare their passive radar tracking with illumination from active radar and the planes’ own transponder signals.

The growing field of passive sensing also includes detecting radar emissions themselves, with souped-up antenna technology that is becoming smaller and more deployable.

Saab unveiled a new product, Sirus Compact, at the Eurosatory defense exhibit outside of Paris, for example. The sensor picks up and characterizes radar emissions, sending the data to higher headquarters for analysis and enabling commanders to determine a suitable strike scenario.

Weighing less than 3 kg, forward-deployed forces can hang the sensor under an aerial drone or mount it on a mast, Pekka Halme, a technical manager with Saab, told Defense News. One deployed sensor – the higher up, the better – can tell the direction of enemy radar emissions, two or more can pinpoint their exact location, he explained.

Sebastian Sprenger is Europe editor for Defense News, reporting on the state of the defense market in the region, and on U.S.-Europe cooperation and multinational investments in defense and global security. He previously served as managing editor for Defense News.

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