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Antenna aperture
Antenna aperture is the area over which an antenna intercepts power from an incoming radio wave. Its effective area is proportional to gain, defined by Harald Friis in 1946.
Antenna deployment mechanism
An antenna deployment mechanism is the mechanical system that stows a spacecraft antenna for launch, releases it in orbit, and moves it into its operating position.
Antenna effect
The antenna effect, also called plasma-induced damage, is gate oxide degradation in integrated-circuit fabrication caused by charge accumulating on conductors during plasma etching and polishing.
Antenna efficiency
Antenna efficiency is the fraction of power delivered to an antenna that it actually radiates rather than dissipating as heat; radiation efficiency counts only ohmic losses, total efficiency also mismatch.
Antenna gain
Antenna gain measures how strongly an antenna radiates or receives in a given direction versus a reference antenna, combining directivity with efficiency and usually quoted in dBi or dBd.
Antenna pattern measurement
Antenna pattern measurement is the experimental determination of an antenna's radiation pattern, gain, and polarization, using far-field ranges, compact ranges, and near-field scanning, as codified in IEEE Std 149-2021.
Antenna selection
Antenna selection is a MIMO wireless communication technique in which only a subset of transmit or receive antennas is connected to RF chains, keeping most performance at lower cost.
Antenna tuner
An antenna tuner, also called an antenna tuning unit (ATU) or transmatch, is a network of adjustable inductors and capacitors that matches an antenna's impedance to a 50-ohm transmitter.
Antenna TV
Antenna TV is an American classic-television digital multicast network launched January 1, 2011 by Tribune Media, now owned by Nexstar, airing 1960s-1970s programming including Johnny Carson reruns from WGN-TV in Chicago, with sister network Rewind TV.
Antennae Galaxies
The Antennae Galaxies, NGC 4038 and NGC 4039, are a pair of colliding spiral galaxies in Corvus, discovered by William Herschel in 1785 and named for their insect-like tidal tails.
Antennae search algorithm
The antennae search algorithm, usually called beetle antennae search (BAS), is a beetle-inspired metaheuristic for continuous optimization that iterates a single candidate solution, reported by Jiang and Li in 2018.
Antennagate
Antennagate was the 2010 controversy over the iPhone 4 losing reception when gripped at its lower-left corner, which Apple answered with a free case for every buyer.
Antennaria
Antennaria (pussytoes) is a genus of about 45 accepted species of dioecious perennial herbs in Asteraceae, tribe Gnaphalieae, native from subarctic and temperate Northern Hemisphere to Mexico and southern South America, known for apomixis and polyploid complexes.
Antenor (crater on Dione)
Antenor is an 81-km impact crater on Saturn's moon Dione at 7.00 S, 11.54 W, named in 1982 after Priam's nephew who founded Padua; Dione craters follow Trojan and Aeneid naming themes.
Anténor Firmin
Anténor Firmin (Joseph Auguste Anténor Firmin, 1850–1911) was a Haitian anthropologist, journalist, and politician whose 1885 book De l'égalité des races humaines rebutted racial hierarchy theories.
Antenora Mons
Antenora Mons is a 122 km mountain feature on Jupiter's moon Io near the north pole, approved by the IAU on January 29, 2025 and named after Antenora, the second ring of Cocytus in Dante's Inferno.
Anteon
Anteon Jurine, 1807 is a cosmopolitan genus of dryinid parasitoid wasps attacking leafhoppers; largest Anteoninae genus with 464 species, extreme sexual dimorphism, and DNA barcoding used to link sexes and delimit species.
Antepartum fetal death
Antepartum fetal death (ICD-11 KD3B.0) is fetal death before the onset of labor, distinct from intrapartum death; maceration suggests antepartum timing, and it accounts for over half of stillbirths.
Antepartum haemorrhage
Antepartum haemorrhage (APH, ICD-11 JA41) is genital tract bleeding in late pregnancy before labour, complicating 2–5% of pregnancies; main causes are placental abruption and placenta praevia, with vasa previa and uterine rupture rarer.
Antera Duke
Antera Duke (ca. 1735–ca. 1809) was an Efik slave-trading chief of Duke Town, Old Calabar, Nigeria, known for his pidgin-English diary of 1785 to 1788.
Anterior cerebral artery
Anterior cerebral artery (ACA), artery of the circle of Willis supplying medial frontal and parietal cortex and corpus callosum; segments A1-A5, variants include azygous ACA and persistent primitive olfactory artery, associated with aneurysms.
Anterior cerebral artery syndrome
Anterior cerebral artery syndrome: stroke deficits from infarction in ACA territory, also called ACA infarction syndrome. Rare (0.3–4.4% of strokes), cardioembolic in origin, with leg-predominant weakness, abulia, alien hand, and akinetic mutism.
Anterior cervical discectomy and fusion
Anterior cervical discectomy and fusion (ACDF) is a spine operation that removes a herniated or degenerative neck disc through the front of the neck and fuses the adjacent vertebrae.
Anterior chamber paracentesis
Anterior chamber paracentesis (ACP) is an ophthalmologic procedure using a fine needle through the cornea to withdraw aqueous humor for diagnostic testing or to lower intraocular pressure.
Anterior cingulate cortex
Anterior cingulate cortex (ACC), including subgenual, pregenual, and anterior midcingulate subregions: medial frontal cortex around the corpus callosum involved in pain affect, conflict monitoring, motor control, and decision-making, targeted by cingulotomy and neuromodulation.
Anterior cruciate ligament
The anterior cruciate ligament (ACL) is one of two cruciate ligaments of the knee, joining femur to tibia and stabilizing the joint against excessive movement.
Anterior cruciate ligament injury
Anterior cruciate ligament (ACL) injury: rupture of the knee ligament preventing tibial forward slide. Over 200,000 US cases yearly, 70% noncontact, females 2-8x higher risk; surgery versus rehabilitation compared in KANON, COMPARE, and ACL SNNAP trials.
Anterior cruciate ligament reconstruction
Anterior cruciate ligament reconstruction (ACLR) is an orthopedic surgical procedure that replaces a torn knee ligament with a tendon graft routed through bone tunnels, restoring knee stability.
Anterior cruciate ligament repair
Anterior cruciate ligament repair is a knee operation that reattaches a patient's own torn ACL rather than replacing it with a graft, as ACL reconstruction does.
Anterior cutaneous nerve entrapment syndrome
Anterior cutaneous nerve entrapment syndrome (ACNES), also called abdominal cutaneous nerve entrapment syndrome or intercostal neuralgia, is entrapment of T7-T12 intercostal nerve branches at the rectus abdominis border, causing chronic localized abdominal wall pain diagnosed by Carnett test and treated with injections or neurectomy.