What can a modern radar tell about a plane 400 km away?

Short answer

At that distance the Boeing E-3 Sentry's pulse-Doppler radar reaches over 250 mi (400 km) against low-flying targets at its operating altitude. Its look-down capability lets it detect, identify and track low-altitude aircraft by filtering out ground clutter. Mission computers correlate tracks and interrogate IFF.

Published: November 4, 2026 · Updated: November 4, 2026 · Edited by Above Ten Thousand · Editorial policy

What can a modern radar tell about a plane 400 km away?

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How far it reaches

The E-3 Sentry's pulse-Doppler radar has a range of more than 250 mi (400 km) against low-flying targets when the aircraft is at its operating altitude, while the pulse (BTH) radar reaches about 400 mi (650 km) against aircraft at medium and high altitude. A mission crew of controllers tracks fighter-sized targets and vectors friendly aircraft to intercept.

What it pulls from the return

The E-3's look-down capability serves to detect, identify and track low-flying aircraft while eliminating ground returns. The radar operates in pulse-Doppler mode, which lets it detect and track moving targets against ground clutter. The onboard mission computers correlate radar tracks, identify friend or foe by interrogating the IFF transponder, and present the air picture to the mission crew on tactical displays.

The program that put it in the air

The E-3s are commonly known as AWACS. In 1963 the USAF requested proposals for an airborne warning and control system (AWACS) to replace its EC-121 Warning Star aircraft, which had served in the airborne early-warning role for more than a decade. Contracts were awarded to Boeing, Douglas and Lockheed, with the latter eliminated in July 1966; in 1967 a parallel program was launched to develop the radar, with Westinghouse Electric and Hughes Aircraft competing for the system. In July 1970 Boeing was selected over McDonnell Douglas's DC-8-based proposal.