SMA connector

SMA connector

Figure 1. Standard male SMA connector: Female body (inside threads) with male inner pin.
Type	RF coaxial connector
General specifications
Diameter	Male: 0.312 in (7.9 mm) HEX
Cable	Coaxial
Passband	Typically 0-18 GHz, some up to 26.5 GHz

SMA (SubMiniature version A) connectors are 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. It offers excellent electrical performance from DC to 17 GHz.

Connector design

The SMA connector consists of a 1/4"-36 thread. The male is equipped with a 0.312" (7.925 mm) hex nut.

In SMA and RP-SMA connectors, the terms "male" and "female" refer exclusively to the male center pin and its female sleeve counterpart rather than to the threads that are used to hold the connection in place. The male connector has inside threads while the female connector has outside threads.

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, an SMA connector is not a good choice for metrological applications.

SMA connectors are rated for 500 mating cycles, but to achieve this it is necessary to properly torque the connector when making the connection. A 5/16 inch torque wrench is required for this, set to 3–5 in·lbf (0.3 to 0.6 N·m) for brass, and 7–10 in·lbf (0.8 to 1.1 N·m) for stainless steel connectors. Flats are sometimes also provided on the cable side of the connector assembly so that a second wrench can be used to prevent it from rotating and damaging the joint to the cable. It is also advisable to clean out loose debris from the internal surfaces with compressed air or a gas duster can before mating.

Variations

The SMA connector is typically rated for mode-free operation from DC to 18 GHz, though some proprietary versions are rated to 26.5 GHz. For performance above this, SMA-like connectors are used. These are the 3.5 mm connector, rated to 34 GHz, and the 2.92 mm (also known as 2.9 mm, SMK, or K type),^[1] good up to 46 GHz. These connectors keep the same outside thread as the SMA, so they can all be cross-mated, however they use an air dielectric, with the center conductors appropriately scaled. However, the life of the precision connector will be reduced, and can be easily damaged when mating with low-grade SMA connectors.

Beyond 46 GHz, the 2.4 mm, 1.85 mm and the 1 mm connector exist. These are similar to the SMA connector, but with the geometries incompatibly scaled. These have mode-free operation to 50, 65, and 110 GHz respectively.

Reverse polarity SMA

Figure 2. Female RP-SMA connector: Female connector body (outside threads) with a male inner pin contact. A male RP-SMA connector is the opposite in both respects — male connector body (inside threads) with a female inner sleeve contact.

Reverse polarity SMA (RP-SMA or RSMA) is a variation of the SMA connector specification which reverses the gender of the interface, as shown in Figures 1 and 2. The term "reverse polarity" here refers only to the gender of the connector's contact pin, not in any way to the signal polarity.

A Female RP-SMA connector is one you will see on your PCI card or WiFi router, and the antenna connected to it has a male RP-SMA connector.

A Female RP-SMA connector has outside threads but has an inner pin (hence reversed), and male RP-SMA connector has inside threads and a center receptacle.

RP-SMA connectors were introduced to separate professional and commercially available equipment, preventing unintentional or intentional connection of high-gain professional antennas with SMA connectors and commercial wireless equipment with RP-SMA connectors, violating federal or international laws. Today, however, both type of connectors are readily available.

The female RP-SMA connector has the same external housing as a standard or conventional female SMA connector, which consists of an outer shell with the threads on the outside; however, the center receptacle is replaced by a male pin. Similarly, the RP-SMA male has threads on the inside like a conventional male, but has a center receptacle instead of the male pin in the middle.

RP-SMA connectors are widely used by Wi-Fi equipment manufacturers to comply with specific local regulations {Section 15.203 Antenna requirement}, e.g., the FCC, which were intended to make it difficult for consumers to connect antennas with gain and thereby breach compliance. However, RP-SMA equipped antennas are now widely available.

See also

• SMB connector, SMC connector
• BNC connector, TNC connector, N connector
• Coaxial cable

References

• Radio-frequency connectors. Part 15: R.F. coaxial connectors with inner diameter of outer conductor 4.13 mm (0.163 in) with screw coupling — Characteristic impedance 50 ohms (Type SMA). International Standard IEC 60169-15, 1979.
• CECC 22110/111
• Connectors, plug, electrical, radio frequency. Military specification sheet MIL-C-39012.
• 47 C.F.R. Section 15.203 Antenna requirements.

External links

Wikimedia Commons has media related to: Connectors or SMA

• RP-SMA connectors
• SMA connectors
• RF Connectors from WA1MBA
• Coaxial SMA Connectors from CMPTER
• SMA Torque Wrench