There are 4 types of 50 Ohm impedance co-axial cable antenna connections which use the SMA (Subminiature version A) connections:
- SMA male has an internal screw thread with a pin in the center,
- SMA female is outside screw thread with a hole in the center
- Reverse polarity SMA male has an inside screw thread with a hole in the center,
- Reverse polarity SMA female has an outside screw thread with a pin in the center.
Please note the term “reverse polarity” (RP) above refers only to the gender of the connector’s contact pin, not to the signal polarity.
In general anything 2.4GHz (eg Bluetooth and WiFi) use the new SMA convention: RP-SMA male on the antennas and RP-SMA female on the modules.
Cellular and GPS (900/1700/1800MHz and 1.57542GHz respectively) use the old convention SMA male for the antennas and SMA female for the modules.
Part of the reason for these confusing connections is that with the advent of mass WiFi radio spectrum regulators did not want easy access to high gain antennas which may cause local area noise and interference with other users.