UPSC Prelims 2026 Q43: Stealth Technology, RAM & Metamaterials
Which of the following statements with regard to stealth technology is/are correct?
1. Stealth objects have a very small radar cross-section and are coated with Radar Absorbing Material.
2. Stealth objects can be detected using specific frequencies.
3. Stealth objects are coated with metamaterials to increase the scattering of electromagnetic radiation.
- 1 only
- 2 and 3 only
- 1 and 2 only
- 1, 2 and 3
Answer: (c) 1 and 2 only
Statement-wise explanation
- 1: correct — Radar cross-section (RCS) is a measure of how large a target looks to a radar, expressed in square metres. Stealth design cuts RCS in two main ways. Shaping (flat, angled facets, aligned edges, hidden engine inlets) sends radar waves away from the radar that transmitted them. Radar Absorbing Material (RAM) coatings, such as iron-ferrite paints and carbon composites, turn the incoming radar energy into heat. A very small RCS and a RAM coating are the two textbook features of a stealth object.
- 2: correct — Stealth reduces detection. It does not make an object invisible. Shaping and RAM are tuned to the higher-frequency bands used by fire-control radars, such as X-band. Low-frequency radars, such as VHF radars at 30–300 MHz, have wavelengths of a metre or more, close to the size of a fin or a wing. At those wavelengths the aircraft scatters by resonance, and both shaping and thin coatings lose much of their effect. Counter-stealth radars use exactly this, so stealth objects can be detected at specific frequencies.
- 3: incorrect — Metamaterials are engineered structures, usually repeating sub-wavelength patterns, that control electromagnetic waves in ways ordinary materials cannot. In stealth they are used as thin, light, broadband absorbers, or to steer reflections away from the radar, so that the radar return gets smaller. The statement gets the purpose backwards. Increasing the scattering of electromagnetic radiation back toward the radar would make the object easier to detect.
How to eliminate
Start with Statement 3. It goes against the whole purpose of stealth. Anything that increases scattering of radar waves makes an object easier to see. Once you drop Statement 3, two options that include it are gone. Statement 1 is the basic definition of stealth, so it is almost certainly true. That leaves '1 only' or '1 and 2 only'. Statement 2 turns on one fact: stealth means low observability, not invisibility, and low-frequency (VHF/UHF) radars can detect stealth aircraft. If you know only that stealth is never absolute, Statement 2 is still the safer choice. Fact to remember: stealth is tuned to particular frequency bands, and long-wavelength radars partly defeat it.
Know more
Stealth (low-observable) technology aims to reduce every signature a platform gives off, not only its radar signature.
Radar cross-section (RCS) is the area a target appears to have to a radar, in m². It depends on shape, material, viewing angle and radar frequency, not just physical size. Cutting RCS sharply shortens the range at which a radar can detect the target.
| Signature | How it is reduced |
|---|---|
| Radar | Shaping (faceted surfaces, aligned edges, internal weapons bays, serpentine inlets); Radar Absorbing Material (RAM); radar-absorbing structures; metamaterial absorbers |
| Infrared (heat) | Shielded or cooled exhaust, mixing hot exhaust with ambient air |
| Acoustic | Quieter engines; on ships and submarines, rafted machinery and anechoic tiles |
| Visual | Camouflage paint, reduced smoke and contrails |
| Electronic | Limiting own radar and radio emissions; passive sensors |
How RAM works: coatings such as ferrite-loaded paints or carbon-based composites turn the energy of an incoming radar wave into heat, so less of it is reflected.
Metamaterials are artificially structured materials whose properties come from their geometry, not their chemistry. They can be made thin and light, absorb across wide frequency bands, and redirect waves. These traits make them strong candidates for next-generation stealth skins.
Limits of stealth:
- Shaping and thin coatings work best against short-wavelength (high-frequency) radars.
- Long-wavelength VHF/UHF radars, multistatic radars (separate transmitter and receiver), and infrared search-and-track can still detect stealth platforms. They are usually less precise for targeting.
Indian context: the Navy's Project 17A (Nilgiri-class) frigates use stealth shaping for a reduced RCS. DRDO labs such as DMSRDE, Kanpur, develop stealth and camouflage materials.
In the news
The Indian Navy commissioned a run of indigenous 'stealth' frigates in 2026, before the Prelims. Dunagiri was delivered in March, and INS Taragiri was commissioned at Visakhapatnam in April. The Navy described Taragiri as having a significantly reduced radar cross-section. This kept the term 'stealth' in the news and made the science behind it likely to be asked.
NCERT Concepts to Revise
- Electromagnetic spectrum: Statement 2 turns on where radar bands sit on the spectrum: low-frequency VHF waves are metre-scale, while fire-control X-band waves are much shorter.
- Electromagnetic radiation: Statements 1 and 3 turn on how a stealth surface handles incoming radar waves, whether it absorbs them, scatters them, or steers them away.