SMA (SubMiniature version A) connectors are semi-precision coaxial RF connectors developed in the 1960s as a minimal connector interface for coaxial cable with a screw-type coupling mechanism. The connector has a 50 Ω impedance. SMA is designed for use from DC (0 Hz) to 18 GHz, and is most commonly used in microwave systems, hand-held radio and mobile telephone antennas, and more recently with WiFi antenna systems and USB software-defined radio dongles. It is also commonly used in radio astronomy, particularly at higher frequencies (5 GHz+).
SMA connectors can be visually confused with the standard household 75-ohm type F coax connector (diameters: Male 7⁄16 inch (11 mm) circular or hex; female 3⁄8 in (9.5 mm) external threads), as there is only about a 2 mm difference overall in the specifications. Type F cannot be mated with SMA connectors without the use of an adapter.
The SMA name is also used for a superficially similar optical fiber connector.