Reading the stealth playbook with world-class electromagnetic measurement

"How precisely you manage invisible electromagnetic waves determines the entire landscape of stealth, radar and defense technology."

Kwon Jae-yong, a senior researcher at the Korea Research Institute of Standards and Science's electromagnetic measurement group, made the remarks Thursday during a meeting with The Herald Business's Pro Pilot team at the KRISS campus in Daejeon. "The outcome of the stealth war no longer hinges on radar output or equipment size," he said. "It depends on how accurately and consistently you can measure electromagnetic waves against a common standard."

The KRISS electromagnetic measurement group Kwon belongs to establishes national measurement standards for electromagnetic waves used in defense, telecommunications and semiconductor applications. Its primary mission is to align and maintain physical quantities — radar power, antenna gain and patterns, the material properties of electromagnetic absorbers, and high-frequency characteristics for semiconductor processes — with international standards across the defense and industrial sectors.

Drawing on what is regarded as a world-leading electromagnetic measurement standard, Kwon independently developed a system that precisely measures radar cross-section (RCS) by combining scale models, terahertz-range frequencies and a robotic platform — without ever suspending an actual fighter jet in the air. The technology quantifies otherwise invisible electromagnetic waves and is emerging as new infrastructure for standardizing "invisible defense technology" across next-generation fighter jets, combat vehicles, drones and even combat uniforms.

The system pairs a six-degrees-of-freedom (6-DOF) robot — capable of moving up, down, left, right, forward and backward as well as rotating — with various scan configurations, enabling electromagnetic measurements across a broad band reaching up to 750 GHz. At frequencies above tens of gigahertz, wavelengths become so short that even a minute positional deviation can significantly skew results. KRISS addressed this by applying position measurement and correction technology to keep antenna alignment error within 10 micrometers — roughly one-seventh the width of a human hair — a level the institute says is among the best in the world and a key indicator of measurement reliability in high-frequency stealth and radar evaluation.

The robot's flexible mobility also dramatically reduces the space and cost constraints that have long burdened large-scale electromagnetic test facilities. Where conventional setups required vast anechoic chambers and fixed antenna and stage equipment, the KRISS system allows the robot to move precisely around airframes, warheads and antennas, enabling repeated high-precision, low-cost tests even in confined spaces.

The system's control and monitoring software and measurement configurations can also be flexibly reconfigured to suit a wide range of targets — from complex-geometry aircraft radars and phased-array antenna modules requiring ultra-precise control to semiconductor package antennas.

In the defense context, the system's greatest significance lies in how it is reshaping the paradigm for RCS evaluation, the standard measure of stealth performance. Conventional methods involved suspending a full-scale aircraft in the air and directing radar at it — a process requiring enormous cost and time just to build a test range capable of supporting a plane up to 20 meters long and 50 meters wide and measuring it from multiple angles.

Kwon's approach is different. Instead of a full-scale aircraft, he uses a scale model reduced to between one-twentieth and one-thirtieth of the original size, then fires millimeter and submillimeter waves in the 300–500 GHz range to match. Because the relationship between an aircraft's size and the wavelength used to probe it is relative, shrinking both by the same ratio allows a small model to reproduce scattering characteristics similar to those of the real thing — a concept known as scale modeling.

Kwon's research targets both sides of the stealth equation — the spear and the shield. High-sensitivity measurement technology and RCS analysis sharpen the spear: the ability to detect stealth targets. Research into developing and applying electromagnetic absorbing materials thickens the shield, making platforms less visible to radar.

Combat uniforms are also in the frame. "Beyond aircraft and tanks, these special materials can be applied to combat uniforms to evaluate how visible a person is from an electromagnetic standpoint," Kwon said. "In an era when drones, satellites and ground-based radar can identify individual soldiers, designing a uniform's RCS and thermal signature is directly tied to battlefield survivability."

In defense, the value of a standard is inseparable from human life. "If you procure a weapon based on specs you cannot trust and then find out on the battlefield that they do not hold up, that is not just a numbers problem — it is a matter of people's lives," he said.

Reducing disputes over inflated or understated specifications in defense export and procurement deals, and verifying that allies are "seeing the same picture" in actual operations, requires an internationally agreed measurement and comparison framework. The electromagnetic measurement standards KRISS is building serve precisely that purpose — invisible defense infrastructure.

"Measurement standards mean making something that can be measured the same way, anywhere, by anyone — scientifically," Kwon said. "Defense is no different. The size of a fighter jet as seen by radar, the detection range of a missile, the effectiveness of a stealth coating — all of these must be defined against the same yardstick before allies can discuss interoperability and before defense export and import negotiations can proceed from a shared understanding."

He added that the group plans to integrate AI to further advance electromagnetic measurement technology in national strategic fields including defense, semiconductors and next-generation communications.