The SMA connector was developed by Amphenol from its line of microwave connectors known as “subminiature A”. The connector has a 3 mm stainless steel ferrule and a connector gap that is threaded on the inside. They are mostly used in military applications.
In addition to their compact size, the SMA connector has exceptional mechanical durability. The ferrule is traditionally made of steel, although ceramic versions are available. SMA connectors types: the SMA-905 has a straight ferrule, the SMA-906 has a stepped ferrule with lower insertion loss. SMA 905 is also available as a keyed connector.