An RP-SMA (Reverse Polarity SMA) RF adapter is a variant of the traditional SMA connector, used to prevent accidental connection to mismatched antennas. The RP-SMA is designed with reversed gender interfaces: the male connector has an inner receptacle instead of a pin, and the female connector has an inner pin instead of a receptacle.
The RP-SMA connector can be identified by its small threaded interface, similar to the standard SMA connector, but with the pin and receptacle switched. It’s crucial to note this difference because, although an RP-SMA and SMA connector can be physically mated, the connection would lack electrical functionality. Every technician has come across this situation at least once in their career.
RP-SMA adapters are commonplace as most RF cables are supplied with standard SMA connectors, but WiFi and specialised wireless equipment is often RP-SMA.