SMA (Sub-Miniature version A) connectors have a 50Ω impedance and offer excellent electrical performance from DC to 18 GHz with semi-rigid cable and a bandwidth of DC to 12 GHz on flexible cables.  They are compact, durable, and commonly used in communications including base stations, test and measurement, and military applications. The SMB (Sub-Miniature version B) connectors are a smaller version of the SMA connector.  They offer the added advantage of snap-on coupling rather than threads which make them ideal for fast connect and disconnect.  These connectors offer excellent electrical performance from DC to 4 GHz.