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An SubMiniature version A (SMA) connector is a coaxial cable connector developed in the 1960s as a semi-precision minimal connector interface with a screw-type coupling mechanism for coaxial cables. This connector features only 50 ohms of impedance and a 1/4-inch-36-thread-type coupling mechanism. It offers excellent performance from 0 to 18 GHz and is usually used as an RF connector for antennas.
The SMA connector is considered a semi-precision, sub-miniature and high-frequency connector that is rated to deliver reliable broadband performance from DC to 18 GHz, with a constant impedance of 50 ohms and low reflection. The main features of this connector are its high mechanical strength and high durability, as evidenced by its robust-looking metal construction.
The male connector is the one with the center pin and inside threads of size 1/4-inch-36, whereas the female connector is the sleeve counterpart that features an outside thread and is used to hold the connection in place. The latter is often placed on and attached to a stable device, whereas the former is located on the detachable wire attachment.
A newer reverse-polarity SMA specification (RP-SMA or RSMA) reverses the polarity of the genders so that the female connector now has the center pin and the male connector has the center receptacle, but the threads and other features remain the same. This was apparently done on purpose by the FCC to prevent home users from damaging sensitive RF equipment when screwing on the antenna.
Some mechanical features of the SMA connector include: