What Is an RF Connector (SMA / BNC / U.FL)?
An RF connector is a connector designed to be impedance-controlled so it carries high-frequency signals with minimal loss and reflection.
Why Special?
At RF the connector's characteristic impedance (usually 50Ω) must match the line. A mismatch causes the signal to reflect and creates RF loss. So RF connectors are made with care.
| Type | Property |
|---|---|
| SMA | Threaded, up to ~18 GHz, antenna |
| BNC | Bayonet, test instrument/coax |
| U.FL / IPEX | Very small, board-antenna pigtail |
SMA
Threaded-lock, robust and common; standard on Wi-Fi/antenna modules. It works with low loss up to a few GHz.
BNC and U.FL
BNC is a bayonet connector plugged with a quarter turn, used on oscilloscope/measurement cables. U.FL is a very small connector used for the antenna pigtail on tiny boards.
Male/Female and RP Types
The male/female distinction in RF connectors concerns both the outer thread and the inner pin. SMA also has a "reverse polarity" (RP-SMA) version: the outer thread stays the same while the inner pin/socket swaps. RP-SMA is standard on most Wi-Fi antennas and, if mixed up with normal SMA, no connection is made.
Common Mistakes
- Impedance: mixing a 75Ω connector/cable instead of 50Ω causes loss/reflection.
- Torque: over-tightening an SMA damages the connector.
- U.FL lifetime: U.FL is for a few plug cycles; frequent unplugging damages it.
Frequently Asked Questions
Why always 50Ω?+
Is U.FL used in the field?+
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