An active electronically scanned array (AESA), also known as active phased array radar (APAR), is a type of phased array radar whose transmitter and receiver (transceiver) 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. Advanced AESA radars can improve on the older passive electronically scanned array (PESA) radars by spreading their signal emissions out across a band of frequencies, which makes it very difficult to detect over background noise, allowing ships and aircraft to broadcast powerful radar signals while still remaining stealthy.