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Active electronically scanned array
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<p>An active electronically scanned array (AESA) is a type of <a href="/facts/Phased_array/5wvA9WLV">phased array</a> antenna, which is a computer-controlled <a href="/facts/Antenna_array/HYRcdJsm">antenna array</a> in which the beam of radio waves can be electronically steered to point in different directions without moving the antenna. In the AESA, each antenna element is connected to a small solid-state transmit/receive module (TRM) under the control of a computer, which performs the functions of a <a href="/facts/Transmitter/nFYghtKv">transmitter</a> and/or <a href="/facts/Receiver_(radio)/5olDTxkg">receiver</a> for the antenna. This contrasts with a <a href="/facts/Passive_electronically_scanned_array/rN66gAr0">passive electronically scanned array</a> (PESA), in which all the antenna elements are connected to a single transmitter and/or receiver through <a href="/facts/Phase_shifter/KdPVsXSL">phase shifters</a> under the control of the computer. AESA's main use is in <a href="/facts/Radar/jk9BTbFA">radar</a>, and these are known as active phased-array radar (APAR). </p><p>The AESA is a more advanced, sophisticated, second-generation of the original PESA phased-array technology. PESAs can only emit a single beam of radio waves at a single frequency at a time. The PESA must utilize a <a href="/facts/Butler_matrix/MY9tSH96">Butler matrix</a> if multiple beams are required. The AESA can radiate multiple beams of radio waves at multiple frequencies simultaneously. AESA radars can spread their signal emissions across a wider range of frequencies, which makes them more difficult to detect over <a href="/facts/Radio_noise/hWt85Gyy">background noise</a>, allowing ships and aircraft to radiate powerful radar signals while still remaining stealthy, as well as being more resistant to jamming. Hybrids of AESA and PESA can also be found, consisting of subarrays that individually resemble PESAs, where each subarray has its own <a href="/facts/RF_front_end/sDwPRPoX">RF front end</a>. Using a hybrid approach, the benefits of AESA (e.g., multiple independent beams) can be realized at a lower cost compared to pure AESA. </p>