https://bulgarianmilitary.com/2024/11/18/russia-floods-ukraine-with-drones-mimicking-large-radar-targets/

By Boyko Nikolov On Nov 18, 2024
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A drone pulled from Kyiv’s reservoir and launched by Russian forces has caught the attention of Ukrainian military researchers. Reports claim this drone is a decoy, costing between $1,000 and $1,300. After being recovered, the drone was disassembled and analyzed by Ukrainian experts.
Russia floods Ukraine with drones mimicking large radar targetsPhoto credit: X

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What piqued the interest of the researchers was the absence of a warhead. Instead, the drone was fitted with a 3D-printed sphere, half-wrapped in foil. This is a Luneberg lens, a type of radar decoy that tricks the Ukrainian air defense systems. The half-foil-wrapped ball is interpreted by radar as a much larger aerial target. According to the Ukrainian researchers, this configuration causes the decoy drone to appear on radar as a Geran-2 [Shahed-136], when, in reality, it is roughly the size of an average human.

In comparison, a Geran-2 drone is reported to cost around $20,000, measuring just over 3.5 meters in length with a wingspan of 2.5 meters. Weighing around 200 kilograms, it carries a payload consisting of a 40-50 kg warhead. Russian sources claim the Geran-2 has an operational range of up to 2,500 kilometers, while the decoy drone has a range of only 600 kilometers, based on Ukrainian observations.

Images circulating online reveal the decoy is relatively lightweight, with one person capable of carrying it over their shoulder. It’s no secret that both warring sides have been using drones made from lightweight materials like cardboard, perforated foil, and honeycomb cardboard for over a year and a half. These inexpensive materials allow for the creation of kamikaze-style drones, which can be used in combat while keeping costs low.

The growing use of these decoy drones poses a significant challenge for air defense systems, particularly given the mismatch in cost between the cheap drones and the expensive interceptors needed to deal with them. With Ukraine and its Western allies relying heavily on advanced and costly air defense systems to intercept larger, more dangerous threats like the Geran-2, the constant diversion of resources to deal with these decoys puts a strain on military budgets and logistics.

The main issue here lies in the cost disparity between these cheap decoys and the much more expensive air defense systems. When Ukrainian air defense systems divert missiles, rockets, or even radar resources to intercept drones with similar characteristics, the costs rise dramatically.

Given that a decoy drone costs between $1,000 and $1,300, and comparing that to the price of air defense missiles or modern interceptors, which can cost tens of thousands of dollars, a significant financial imbalance is created. Western allies providing such technologies to Ukraine are likely also facing increasing costs, as the supply of high-quality air defense systems becomes more essential to counter the increasingly innovative Russian drones.

There’s no doubt that this problem is not only local. Ukraine’s allies, who provide expensive air defense systems, are also under economic strain, as the effectiveness of these systems can be severely reduced if part of their resources are used to intercept cheap decoys. In the long term, this could lead to significant depletion of missiles and other resources that could be better directed at more important and larger threats. Any inefficient use of these assets puts stress on the logistics chain and raises strategic concerns regarding the sustainability of air defense resources.

The Luneberg lens is an optical device that creates the effect of focusing a radiated signal used by radar systems. It consists of a hemisphere with a variable refractive index, which is the core principle behind its operation. This element is designed to manipulate radio waves in such a way that they are reflected in a specific manner, creating the illusion of a much larger target than the actual object.

The technology of the Luneberg lens utilizes the physical property of materials with a varying refractive index, and its purpose is to manipulate how radio waves are reflected and spread after encountering the object.

Radar systems typically determine the size of a target by analyzing the reflected radio waves and comparing them to known models of different types of objects. This information allows them to classify targets by size and threat level. The Luneberg lens, through its optical properties, causes the radio waves to appear as if they are coming from an object of a different size and shape. For example, a drone equipped with such a lens can appear on radar as something much larger than it actually is.

The physical principle underlying the Luneberg lens is related to the refraction of light or radio waves as they pass through different media with varying refractive indices. The lens is designed so that its refractive index changes smoothly due to its geometry and material, resulting in specific deflection of the radio waves. This deflection causes the radar image to expand, creating the illusion of a larger target.

When the radar encounters this type of decoy, as a result of the refraction that occurs through the lens, it interprets the signal as coming from a large object, such as a missile or large aircraft, rather than a small drone. This creates the apparent deception that the target is significantly larger than it truly is. The lens not only affects the size of the target but can also alter the angle of reflection of the signal, further masking the true nature of the object.

These characteristics of the Luneberg lens make decoys equipped with it highly effective against radar systems. The ability to manipulate the signals in this way leads to challenges for air defense systems, which must commit resources to detecting and destroying false targets. As a result, a significant portion of the defense system may be engaged with fake threats that are perceived as real, leading to considerable costs and resource depletion.

The key feature of the lens is that its refractive index is designed to change in such a way that it creates an expanding sphere that adjusts the spread of radio waves. This function is specifically developed to simulate a large object, while also concealing the true size of the drones on which it is mounted.