SMA Connectors

You must carefully inspect a SMA connector prior to mating with a precision 3.5 mm connector (this includes a new SMA connector). This must be both a visual and mechanical inspection. Use a precision connector gauge designed to measure SMA connectors. Remember that gauging SMA connectors is the most important step you can take to prevent damaging your equipment. Significant structural and dimensional differences exist between these SMA and precision connectors. Precision 3.5 mm connectors, also known as APC-3.5 connectors, are air-dielectric devices. Only air exists between the center and outer conductors. The male or female center conductor is supported by a plastic "bead" within the connector. On the other hand, a plastic dielectric supports the entire length of the center conductor of an SMA connector. In addition, the diameter of both the center and outer conductors of SMA connectors differ from that of a precision 3.5 mm connector. When an SMA connector is mated with a precision 3.5 mm connector, the connection exhibits a continuity mismatch (SWR), typically about 1.10 at 20 GHz. This continuity mismatch is less than the mismatch that occurs when precision 3.5 mm connectors are mated. Please keep this mismatch in mind when making measurements on SMA and precision 3.5 mm coupled junctions.