Transmit/Receive modules
An AESA face holds 1,000–2,000 T/R modules, each the size of a matchbox. Each contains a gallium-nitride (GaN) power amplifier, a low-noise receiver, a phase shifter and an attenuator. Failing modules degrade performance gracefully — losing 10% of modules costs only 1 dB of gain, where a mechanical radar with one failed transmitter is dead.
Beam agility
Because steering is electronic, the beam can jump anywhere in the field of view in microseconds. One pulse searches; the next tracks a missile; the next illuminates a target for a semi-active missile; the next is a data link to a wingman. The APG-81 on the F-35 interleaves all of these in real time.
Low probability of intercept
AESA can spread its energy across frequency and time so that an enemy radar warning receiver sees noise, not a radar. Frequency hops every pulse, pulse width and PRF jitter, and beam dwell times measured in microseconds make detection by classical RWRs very hard. This is why fifth-generation fighters can light up targets without warning the target it is being illuminated.
Cost and cooling
AESA is expensive — a fighter radar can cost several million dollars — and the T/R modules generate serious heat. Liquid cooling is standard. But the reliability gains (MTBF measured in thousands of hours vs hundreds for mechanical radars) and capability gains have made AESA the only acceptable choice for modern combat aircraft.