SMA connector is semi-precision coaxial RF connectors developed 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+).