SMA connector
Figure 1. Standard male SMA connector: male body (inside threads) with male inner pin.
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| Type | RF coaxial connector | ||
|---|---|---|---|
| Diameter | Male: 0.312 in (7.9 mm) HEX | ||
| Cable | Coaxial | ||
| Passband | Typically 0–18 GHz, some up to 26.5 GHz |
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SMA (SubMiniature version A) connectors are semi-precision coaxial RF connectors developed in the 1960s as a minimal connector interface for coaxial cable with a screw-type coupling mechanism. The connector has a 50 Ω impedance. SMA is designed for use from DC to 18 GHz, but is most commonly used for hand-held radio and mobile telephone antennas, and more recently with WiFi antenna systems and USB Software Defined Radio dongles.
SMA connectors can be visually confused with the standard household 75-ohm type F coax connector (diameters: Male 7⁄16 inch (11 mm) circular or hex; female 3⁄8 in (9.5 mm) external threads), as there is only about a 2 mm difference overall in the specifications. Type F cannot be mated with SMA; this connection is possible using an adapter.
The SMA name is also used for a superficially similar optical fiber connector.
The SMA connector employs a 1/4-inch diameter, 36-thread-per-inch threaded barrel. The male is equipped with a hex nut measuring 5/16 inch (0.3125 inch / 7.9 mm) across opposite flats, thus taking the same wrench as a #6 SAE hex nut.
A standard-polarity SMA male connector has a center pin surrounded by barrel with inside threads, and the standard SMA female connector has a center sleeve surrounded by a barrel with outside threads. As with most other connectors, the gender assignment thus corresponds to the innermost electrical component. There are also reverse-polarity ("RP") SMA connectors in which the pin and sleeve are swapped; so that the "male" RP-SMA has a center sleeve surrounded by an inside-threaded barrel, and the "female" RP-SMA has a center pin and an outside-threaded barrel. See below for a fuller description.
The SMA connector uses a polytetrafluoroethylene (PTFE) dielectric which will contact along the mating plane. Variability in the construction and the mating of the connectors limit the repeatability of the connector impedance. For that reason and that they are just rated for a limited number of connection cycles, an SMA connector is not usually a good choice for metrological applications.
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