This work of Polish engineers doesn't look like radar. It allows you to observe without being detected.

• At last week's defense fair in Kielce, the Ministry of National Defense's Armament Agency purchased 28 PET/PCL passive tracking radars manufactured by PIT-Radwar in Warsaw for PLN 3.9 billion. The agreement also includes an option for another 18 devices for PLN 1.9 billion.
• Passive location radars do not emit radio waves themselves. Instead, they detect waves emitted by aircraft, helicopters, and drones, as well as the reflected waves from airborne transmitters such as television towers or cellular networks. Polish passive radars are among the few in the world to combine these two methods.
• For now, the devices will be used to initially detect targets, but Polish engineers want to improve them to the point where they can be used to guide weapons.
• We will discuss challenges facing the military and the economy during the "Defense Industry" conference. The event will take place on October 15 at the International Congress Center in Katowice.

The Armaments Agency, subordinate to the Ministry of Defense, signed a contract last week for passive location systems . These radars don't operate like the devices seen at airports or ships. A typical radar is active, meaning it emits radio waves that bounce off objects it encounters and return to the device. Passive location systems don't emit anything, but use waves originating from other sources .

Marek Borejko, president of PIT-Radwar and one of Poland's leading radiolocation specialists, explained in an interview with WNP that it's a passive sensor, just like the human eye or ear. "The eye doesn't emit any waves, but we observe what the sun or moon illuminates. A passive location sensor is a radio receiver, so it's difficult to detect because it doesn't emit anything; it simply listens. We listen for everything that reflects off objects in the air, which is illuminated by a different electromagnetic wave," said the president of PIT-Radwar, a Warsaw-based radar manufacturer owned by Polska Grupa Zbrojeniowa.

PET and PCL. What methods do passive radars use?

Today, many devices emit radio waves in space. Two subsystems, the Passive Emitter Tracking (PET) and Passive Coherent Location (PCL) , utilize this capability. PET detects signals generated by transmitters operating on airborne objects. These include airborne radars, communication links, Inter-Friendly-Foe (IFF) systems, and navigation systems. PCL utilizes signals from devices other than radar and aircraft, primarily cellular, radio, and television transmitters.

"There are many sources of electromagnetic waves. An object moving through the air reflects and scatters these waves, and an intelligent device on the ground 'listens' to these reflections," Borejko explained.

He compared passive location radars to a person's two ears. We can determine where a sound is coming from based on which ear hears it first. It's similar with passive radars – an object's position in the air is determined based on the time differences between scattered waves reaching sensors on the ground. "Therefore, the basic element of a passive location system is a minimum of two radars, preferably three, and in fact, in our solution, we use four. With four , we can very precisely determine both distance and altitude ," said the WNP interlocutor.

"There are always waves in the air"

He also explained that PCL listens to the signal from transmitters on the ground and checks whether a signal with the same characteristics has not been reflected by an object in the air.

If such a reflection is detected, the detected object is classified. How this is done is one of the most closely guarded secrets of every radar, not just the Polish passive location system. In simple terms, President Borejko compares it to how a person recognizes a caller by their voice timbre, for example, on the telephone. "Every person has a distinctive voice tone. Similarly, an object in the air illuminated by a given wavelength behaves characteristically, and based on this, we can classify what it is," said the head of PIT-Radwar.

If, during wartime, ground-based civilian transmitters—such as the aforementioned cellular telephones, radio broadcasting, and television—are lacking, there's always the PET subsystem, which detects radiation emitted by devices on board enemy aircraft, helicopters, or unmanned aerial vehicles. The PCL subsystem, on the other hand, can still operate, but using, for example, waves emitted by other active radars, both our own and those of the enemy. However, these aren't the only sources of radio waves expected to be active during conflict.

"Experience from Ukraine shows that the battlefield is highly saturated with electromagnetic waves. Even individual soldiers know that drones are approaching them because they are equipped with small spectrum analyzers that show that a source of electromagnetic waves has appeared in the air. There are always some waves in the air," said Borejko.

The biggest advantage of passive radars

Every radar is a valuable target for the enemy. Active radar, like most radars in the world, emits its own radio waves and can therefore be compared to a very large, highly visible light bulb. To destroy such radars, a separate class of anti-radar missiles, guided by the source of the emission, was developed in the early decades of the Cold War. However, they are not suitable for destroying passive radars, precisely because passive radars emit nothing. This is their greatest advantage in the event of armed conflict .

Moreover, Borejko pointed out that passive radars have multiple antennas spaced apart. Therefore, radio waves reach them after being reflected from an object at different angles, which in turn allows them to "see" more.

Today, it is used for preliminary target detection, and in the future, perhaps for weapon guidance.

The passive location systems purchased by the Ministry of National Defense are intended primarily for initial target detection and transmission of information to active radars. Will this be the end? "The goal is to design a passive radar with the accuracy necessary to guide weapons," Borejko told CIS.

He added that while there are passive radars in the world that use either the PET or PCL system, the Polish passive location system is the first solution using a fusion of these two technologies .

The PET/PCL passive location radar project has been underway since 2012. When asked why it took so long to sign the contract with the military, Borejko replied that it's important to remember that technology is evolving rapidly, and sometimes the computer components on which research and development began are no longer available on the market by the time it ends. "At the last minute, we had to really push ourselves to choose solutions that would last for many years," he explained.

He added that passive location technology was new on the market and there was no knowledge on the market about how to check the results of research and development work.

Contract for PLN 3.9 billion plus option

On September 2, the Armament Agency ordered a total of 46 PET/PCL passive tracking radars . The contract is divided into two parts. The guaranteed order covers 28 devices for PLN 3.9 billion gross. An additional 18 devices are available for option at PLN 1.9 billion . Deliveries are scheduled for 2030-38.

The radars are designed for the Narew short-range air defense missile system. This is the mid-level system of the air and missile defense system being developed by Poland. However, the Armament Agency stated that the technical and functional advantages of the PET/PCL passive radars also allow their use in the Wisła system. This is the military's term for medium-range air defense, which in Poland is the top level of the system equipped with Patriot missile launchers.

At last week's International Defense Industry Exhibition in Kielce, the Armament Agency signed an agreement with the PGZ-Narew consortium, led by the state-owned Polish Armaments Group (PGZ-Narew), and including subsidiaries: Huta Stalowa Wola, Jelcz, Mesko, the Maritime Technology Research and Development Center, PCO, PIT-Radwar, Military Communication Works No. 1, Military Armament Works, Military Electronic Works, and Tarnów Mechanical Works. However, the manufacturer of the passive location systems is PIT-Radwar, which has developed and continues to develop them in collaboration with AM Technologies and the Warsaw University of Technology .

In a full configuration, a single array consists of four passive location radars spaced a certain distance apart. A configuration with fewer radars is possible, but this limits the use of data from the PET subsystem. However, even a single radar can locate and track airborne objects, albeit within a limited area.

In mid-July, in response to an interpellation from a group of PiS MPs, Deputy Defense Minister Paweł Bejda announced that 63 sets of passive tracking systems, each containing four devices, are planned to be acquired by 2035. Accordingly, we should expect further orders.