An active electronically scanned array (AESA), also known as active phased array radar is a type of phased array radar whose transmitter and receiver functions are composed of numerous small solid-state transmit/receive modules (TRMs). AESA radars aim their "beam" by emitting separate radio waves from each module that interfere constructively at certain angles in front of the antenna. They improve on the older passive electronically scanned radars by spreading their signal emissions out across a band of frequencies, which makes it very difficult to detect over background noise. AESAs allow ships and aircraft to broadcast powerful radar signals while still remaining stealthy.
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