SMA connector
Encyclopedia
SMA connectors are coaxial
RF connector
s 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 18 GHz
.
In SMA and RP-SMA connectors, the terms "male" and "female" refer exclusively to location of the threads. Male connector has inside threads and 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 before mating.
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 (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.
Female RP-SMA connector is one you will see on your PCI card or WIFI router, and Antenna connected to it has male RP-SMA connector.
Female RP-SMA connector has outside threads but has inner pin (hence reversed), and male RP-SMA connector has inside threads and pin hole in the middle.
RP-SMA connectors were introduced to separate professional and commercially available equipment, preventing unintentional or intentional connection of high-gain professional antennas with SMA connector and commercial wireless equipment with RP-SMA connector, 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 plug, which consists of an outer shell with the thread on the inside; however, inner pin hole is replaced by a pin. Similarly, an RP-SMA male has threads on the inside like a conventional male, but is has pin hole instead of the 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.
Coaxial
In geometry, coaxial means that two or more forms share a common axis; it is the three-dimensional linear analogue of concentric.Coaxial cable, as a common example, has a wire conductor in the centre a circumferential outer conductor and an insulating medium called the dielectric separating...
RF connector
RF connector
A coaxial RF connector is an electrical connector designed to work at radio frequencies in the multi-megahertz range.RF connectors are typically used with coaxial cables and are designed to maintain the shielding that the coaxial design offers. Better models also minimize the change in transmission...
s developed in the 1960s as a minimal connector interface
Electrical connector
An electrical connector is an electro-mechanical device for joining electrical circuits as an interface using a mechanical assembly. The connection may be temporary, as for portable equipment, require a tool for assembly and removal, or serve as a permanent electrical joint between two wires or...
for coaxial cable
Coaxial cable
Coaxial cable, or coax, has an inner conductor surrounded by a flexible, tubular insulating layer, surrounded by a tubular conducting shield. The term coaxial comes from the inner conductor and the outer shield sharing the same geometric axis...
with a screw type coupling mechanism. The connector has a 50 Ω impedance
Electrical impedance
Electrical impedance, or simply impedance, is the measure of the opposition that an electrical circuit presents to the passage of a current when a voltage is applied. In quantitative terms, it is the complex ratio of the voltage to the current in an alternating current circuit...
. It offers excellent electrical performance from DC
Direct current
Direct current is the unidirectional flow of electric charge. Direct current is produced by such sources as batteries, thermocouples, solar cells, and commutator-type electric machines of the dynamo type. Direct current may flow in a conductor such as a wire, but can also flow through...
to 18 GHz
GHZ
GHZ or GHz may refer to:# Gigahertz .# Greenberger-Horne-Zeilinger state — a quantum entanglement of three particles.# Galactic Habitable Zone — the region of a galaxy that is favorable to the formation of life....
.
Connector design
The SMA connector consists of a 0.250x36 thread. The male is equipped with a .312 inch (7.925mm) hex nut.In SMA and RP-SMA connectors, the terms "male" and "female" refer exclusively to location of the threads. Male connector has inside threads and female connector has outside threads.
The SMA connector uses a polytetrafluoroethylene
Polytetrafluoroethylene
Polytetrafluoroethylene is a synthetic fluoropolymer of tetrafluoroethylene that finds numerous applications. PTFE is most well known by the DuPont brand name Teflon....
(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
Metrology
Metrology is the science of measurement. Metrology includes all theoretical and practical aspects of measurement. The word comes from Greek μέτρον , "measure" + "λόγος" , amongst others meaning "speech, oration, discourse, quote, study, calculation, reason"...
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
Pound-foot (torque)
A pound-foot is a unit of torque . One pound-foot is the torque created by one pound force acting at a perpendicular distance of one foot from a pivot point....
(0.3 to 0.6 N·m
Newton metre
A newton metre is a unit of torque in the SI system. The symbolic form is N m or N·m, and sometimes hyphenated newton-metre...
) for brass, and 7–10 in·lbf
Pound-foot (torque)
A pound-foot is a unit of torque . One pound-foot is the torque created by one pound force acting at a perpendicular distance of one foot from a pivot point....
(0.8 to 1.1 N·m
Newton metre
A newton metre is a unit of torque in the SI system. The symbolic form is N m or N·m, and sometimes hyphenated newton-metre...
) 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 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 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
Female RP-SMA connector is one you will see on your PCI card or WIFI router, and Antenna connected to it has male RP-SMA connector.
Female RP-SMA connector has outside threads but has inner pin (hence reversed), and male RP-SMA connector has inside threads and pin hole in the middle.
RP-SMA connectors were introduced to separate professional and commercially available equipment, preventing unintentional or intentional connection of high-gain professional antennas with SMA connector and commercial wireless equipment with RP-SMA connector, 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 plug, which consists of an outer shell with the thread on the inside; however, inner pin hole is replaced by a pin. Similarly, an RP-SMA male has threads on the inside like a conventional male, but is has pin hole instead of the pin in the middle.
| Male central Pin | Female central Receptacle | |
|---|---|---|
| Inside Thread | SMA Male | Reverse SMA Male |
| Outside Thread | Reverse SMA Female | SMA Female |
RP-SMA connectors are widely used by Wi-Fi
Wi-Fi
Wi-Fi or Wifi, is a mechanism for wirelessly connecting electronic devices. A device enabled with Wi-Fi, such as a personal computer, video game console, smartphone, or digital audio player, can connect to the Internet via a wireless network access point. An access point has a range of about 20...
equipment manufacturers to comply with specific local regulations {Section 15.203 Antenna requirement}, e.g. the FCC
Federal Communications Commission
The Federal Communications Commission is an independent agency of the United States government, created, Congressional statute , and with the majority of its commissioners appointed by the current President. The FCC works towards six goals in the areas of broadband, competition, the spectrum, the...
, which were intended to make it difficult for consumers to connect antennas with gain
Gain
In electronics, gain is a measure of the ability of a circuit to increase the power or amplitude of a signal from the input to the output. It is usually defined as the mean ratio of the signal output of a system to the signal input of the same system. It may also be defined on a logarithmic scale,...
and thereby breach compliance. However, RP-SMA equipped antennas are now widely available.
See also
- N connectorN connectorThe N connector is a threaded RF connector used to join coaxial cables. It was one of the first connectors capable of carrying microwave-frequency signals, and was invented in the 1940s by Paul Neill of Bell Labs, after whom the connector is named.-Design:Originally, the connector was designed to...
- SMB connectorSMB connectorSMB connectors are coaxial RF connectors developed in the 1960s. SMB connectors are smaller than SMA connectors.They feature a snap-on coupling and are available in either 50 Ω or 75 Ω impedance...
- SMC connectorSMC connectorSMC connectors are coaxial RF connectors developed in the 1960s. They use a #10-32 UNF threaded interface and are available in 50 Ω or 75 Ω impedances...
- TNC connector, also has RP-TNC version used for Wi-Fi