SMA connector

SMA connector

Figure 1. Standard male SMA connector: male 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 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. It is designed for use from DC to 18 GHz.

Connector design

The SMA connector consists of a 1/4"-36 thread. The male is equipped with a 0.312" (5/16") 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 and the fact they are just rated for a limited number of connection cycles, an SMA connector is not usually a good choice for metrological applications.

SMA connectors are rated for up to 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 inspect and 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), 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 precision connector 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. 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. NB: this is very confusing to many people, as they (incorrectly) assume that a connector labeled "male" must have a pin. Despite this confusion, the overwhelming industry convention for RP-SMA is clearly different as shown by the previous references. The difference in the RP-SMA interface was required by the FCC so that consumer-level equipment (using RP-SMA connections) cannot physically mate with professional grade (and typically higher-gain) equipment (using SMA connections).

	Center Pin	Center Receptacle
Inside Thread	SMA Male	RP-SMA Male/Plug
Outside Thread	RP-SMA Female/Jack	SMA Female

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. 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

• SMA & RP-SMA Antenna Cable Connector Types: Photo Gallery / Gender & Compatibility - Data-Alliance.net
• 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

• RF Connectors from WA1MBA
• SMA from CMPTER