RP stands for "reverse polarity". An RP-SMA antenna is designed to prevent the unauthorized connection of an external antenna to increase the range. In an RP-SMA connector, the gender has been changed. The RP-SMA male is also the connector with inside threads, but it has the metal sleeve as an inner conductor. The RP-SMA female socket has a barrel with external threads and a center pin.
When they are plugged in, the two are indistinguishable and the signal quality is the same. Although an RP-SMA plug fits mechanically into an SMA socket, it does not fit electronically. Such a connection is not functional.