Countering Stealth

When introduced in 1988 with the unveiling of the Lockheed F-117 Nighthawk fighter, stealth proved to be a game changing technology that turned the clock back for the erstwhile Soviet Union, which had nearly caught up with the West in military aviation technology. Stealth succeeded decisively because it proved expensive to emulate and difficult to counter for US adversaries. What does the future portend for stealth?

- Vijainder K Thakur

Stealth Overview

Stealth or Low Observability (LO), in aircraft is achieved by impairing an adversary's ability to detect the aircraft. Aerial threats can be detected using active sensors such as radars or passive electro optical, IR and electronic sensors. Because of its accuracy and effectiveness under all ambient conditions, radar is the preferred sensor. Therefore, stealth focuses heavily on eluding radar detection.

Radar Stealth

Electromagnetic radiation from a radar scatters from bodies smaller than the wavelength of the radiation. Some of the scattered radiation is reflected right back to the transmitter/receiver (Tx/Rx) of the radar resulting in a 'radar signature.' Radar stealth is achieved through airframe shaping that deflects (bounces off) radiation, instead of scattering it.

The effectiveness of the stealth shaping depends on the wavelength at which the radar is operating. If target size is greater than the radar wavelength, emissions are mostly deflected (bounced off); very little radiation is reflected back to the Tx/Rs resulting in a low 'radar signature'.

Shaping features, good at 3 cm radar wavelength are ineffective at 1 m wavelength; the radiation is scattered over a wide range of angles.

Tactical fighter-sized stealth aircraft such as the F-22 or F-35 are shaped to deflect wavelengths ranging from decimetre S-Band through centimetre X-band to sub-centimetre Ku-band; the band range in which most surveillance radars, acquisition radars, surface-to-air missile engagement radars, fighter-borne air intercept radars, and missile radar seekers operate.