What is Subminiature A Connector (SMA)?
A subminiature A connector (SMA) is a coaxial cable connector that was developed in the 1960s as a semi-precise minimal connector interface with a screw coupling mechanism for coaxial cables.
This connector offers only 50 ohm impedance and a 1/4 inch 36 threaded coupling mechanism. It has excellent 0-18GHz performance and is typically used as an RF connector for antennas.
The SMA connector is a semi-precision, sub-miniature and high frequency connector designed for 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 long service life, as evidenced by its robust-looking metal construction.
The male connector is the one with the center pin and 1/4-inch-36 internally threaded while the female connector is the mating sleeve which is externally threaded and used to hold the connection in place. The latter is often placed on and attached to a sturdy device while the former is on the removable wire attachment.
A more recent reverse polarity SMA specification (RP-SMA or RSMA) reverses the polarity of the sexes so that the jack now has the center pin and the plug has the center jack, but the threads and other features remain the same. This was apparently done deliberately by the FCC to prevent home users from damaging sensitive RF equipment when screwing on the antenna.
Some mechanical properties of the SMA connector include:
- It uses a 1/4 inch 36 threaded coupling mechanism.
- The connector is equipped with a 5/16 "hex nut to allow torque with a 1/2" wrench.
- The socket has a 4.32 mm long thread for the coupling.
- It has a silicone rubber O-ring that separates the main body and union nut for dust resistance.