SMA (SubMiniature version A) connectors are coaxial RF connectors developed in the 1960's as a minimal connector interface for coaxial cable with a screw type coupling mechanism. The connector has a 50 Î© impedance. It offers excellent electrical performance from DC to 18 GHz. SMA and precision SMA-like connectors are by far the most popular coaxial connector, though by modern standards, their performance and durability are somewhat limited.
The SMA connector consists of a 0.250x36 thread. The male is equipped with a .312 inch hex nut. It is important that the nut be properly torqued with a 5/16 inch wrench, 3-5 in-lbs for brass, and 7-10 in-lbs for stainless steel connectors. When turning the nut, it is very important that the remainder of the connector does not rotate, otherwise premature wear of the connector will result. Furthermore, the connector should be carefully inspected before each use, and any debris cleaned with compressed air. When properly handled, a SMA connector should remain within specified performance through 500 mating cycles.
The SMA connector uses a PTFE dielectric which will contact along the mating plane. Variablilty in the construction and the mating of the connectors limit the repeatability of the connector impedance. For that reason, a SMA connector is not a good choice for metrology applications.