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RP-SMA Cables & Adapters

 

Versions & Dimensions of RP-SMA connectors

RP-SMA Connector Dimensions RP-SMA Diameter
Hex Net for RP-SMA-female bulkhead connector:  Dimensions RP-SMA female connector Flange options:  7/16-inch and 5/16-inch
L-mount bracket for antenna with RP-SMA Connector

RP-SMA Connector Characteristics and Details

  • RP-SMA female and male diameter:
    • RP-SMA female outside diameter is 5/16" (7.9375mm): Accommodates a hex nut (bulkhead nut) with 5/16" nominal outer diameter
    • RP-SMA male inside diameter is 5/16" (7.9375mm) (the inside diameter where the threads are).
  • RP-SMA Gender Determination:  Key Points
    • RP-SMA gender is counter-intuitive: Please observe picture & note it is correct.  
    • The gender is referring to the pins inside--not the threads. RP-SMA male has threads on inside.
    • RP-SMA male has a socket inside rather than a pin, as you might expect, because the RP stands for "Reverse Polarity."  The socket/pin configuration is female when it appears to be male, and vice versa.
    • More details regarding RP-SMA gender determination.
  • Other RP-SMA Characteristics and Key Points
    • RP-SMA-male is also called "plug" and SMA female connector is also called "jack"
    • We offer an RP-SMA wrench to assist in installing antennas, cables and adapters with RP-SMA or SMA connector(s).
    • RP-SMA-male connector fits items that have an SMA-female connector.
    • RP-SMA is a round screw-type connector, with medium-sized, threaded coupling connectors that are rated for frequencies from the lowest (DC) up to 18GHz.
    • RP-SMA connectors are not compatible with the common, commercially available Type F coaxial connector. Type F connectors look similar but are of slightly different size and will not pair with RP-SMA or SMA connectors without an adapter.
    • We offer an RPSMA wrench to assist in installing antennas, cables and adapters with SMA or RP-SMA connector(s).
    • RP SMA is also known as SMA RP, SMA-R, SMA-RP, SMA R

RP-SMA connectors:  Deep Dive into the Details

An RP-SMA connector is a type of electrical connector which is used to transmit radio frequency signals across junctions between coaxial cables. They are able to maintain the signal transmission with similar shielding and electrical performance as the cabling as well as providing a secure mechanical union for cable lengths or attached peripherals. Sma reverse polarity connectors are a variant of the standard Sub-Miniature version A connector, which has been in widespread use since the 1960s. The RP in the name stands for Reverse Polarity and regards the gender of the inner interface ( male pin and female receptacle) which is reversed from the SMA's orientation. The RP SMA connector is the same as an equivalent SMA connector in all other respects.

Reverse polarity SMA connectors are:

  • Semi-precision. This means that the dimensions of these connectors carry a high degree of accuracy; to within 1/68th to 1/100th of an inch.
  • Sub-miniature. This class of radio frequency connector was one of the smallest and most compact designs of its day, though it has been superseded by far smaller coaxial connectors.
  • High frequency. These connectors are effective at conducting both sub-microwave and microwave frequencies of up to 18 GHz. This means that they provide good broadband performance in a range of applications and settings.

They are an excellent choice for creating strong and secure electrical connections, and their robust design withstands mechanical stress and environmental exposure.

The key physical and electrical features of this connector class are explored below.

Physical characteristics of the RP SMA connector

These connectors are typically fabricated in line with the military specification MIL-STD-348. They consist of:

  • A threaded body
  • A coupling 5/16 inch hex nut
  • A silicone rubber gasket
  • An inner gendered conductive interface with either a female pin or male receptacle surrounded by an insulator.
  • A crimp ferrule

The body of the connector is made from brass or gold-plated brass, but comparable designs can be made using stainless steel with copper or nickel passivation to protect against corrosion.

Shape and dimensions

Though not the smallest of coax connectors, the RP SMA still can be considered small. A standard RP SMA connector typically has a length of 18.16mm (0.715 inches), and a diameter of 7.92mm (0.312 inches). A male RP SMA connector or female SMA connector has a weight of just over 4 grams (0.009 lbs).

Gender

Reverse Polarity SMA connectors differ from the standard polarity SMA, because of the reversal of the gender of the mating interface, specifically the contact pin and receptacle. It is a physical characteristic and has no effect on the electrical profile or performance of the connector. The outer housing of the contractor remains identical to the standard polarity SMA.

Like the standard SMA connector:

  • the female RP SMA jack has an outer housing that has externalized threads.
  • the male connector has its threads on the inside of its housing.

But, unlike the standard polarity SMA:

  • the rp sma female possesses a male pin at its center.
  • the male connector has a center receptacle rather than a pin.

The brass or copper connector is gold plated and surrounded by a PTFE insulator.

This difference makes rp sma connectors completely incompatible with their SMA counterparts. Even if a female SMA and male RP SMA are screwed together there is no union of the inner connectors meaning transmission cannot occur via this combination.

Body geometry

This popular category of connector is commonly available in either a straight or right-angle orientation to accommodate coax cable assemblies in locations where space may be a challenge. Other modified RP SMA connector configurations are available and include:

  • Bulkhead feedthrough
  • Panel mount

as well as RP SMA plugs and jacks for printed circuit boards.

Coupling of RP-SMA connectors.

RP-SMA connectors are threaded for coupling by screwing the male and female connectors together. The threading on the connectors, internal in the male and external on the female is 36 threads per inch. The male connector screws down over the female connector. Within the connector, the male pin is inserted into the female receptacle for a secure and reliable connection. An RP SMA socket and SMA plug are able to make a mechanical connection by screw-on coupling but not an electrical one.

The RP SMA connector has a mating torque of 3 to 5 in-lbs and can be tightened with a suitable connector wrench. Their robust design ensures reliability for a high number of mating cycles and 500 cycles can easily be achieved if proper torque is applied when connecting.

Electrical profile of the reverse polarity SMA connector

The electrical characteristics of the RP SMA connector are identical to those of a standard SMA connector. This radio frequency connector has proven performance in:

  • Handling high-frequency radio frequency transmission in the GHz range.
  • Maintaining the shielding of the coaxial cable it is connected to.
  • Maintenance of transmission line impedance.
  • Keeping signal reflection and power loss to an absolute minimum.
  • Preventing electromagnetic interference from affecting signal transmission through the connector.

The frequency range of the reverse polarity SMA connector

As transmission frequency increases, any electrical variation between the coaxial cable and the connector are amplified. RP SMA connectors are engineered to minimize these effects They deliver reliable performance for mode free operation at frequencies between DC and up to 18 GHz when a straight oriented R-SMA is attached to semi-rigid or semi-flex cable.

The RP-SMA connector impedance of 50 ohms matches the impedance of the most common types of cable it is connected to. Impedance mismatching will produce reflections.

RP SMA VSWR

The efficiency of transmission of RF power from the source through the connector is measured by the Voltage Standing Wave Ratio. The typical RP SMA VSWR lies between 1.05 and 1.25 f in GHz and will depend on the coax cable it is connected to.

The resistance of the PTFE insulation of the R-SMA connector is high at over 5000 megaohms. At 2 to 3 GHz, radiofrequency loss across this connector is approximately -90dB per minute. 

Why are RP SMA connectors important?

The SMA connector from which the RP SMA connector is derived was invented in the late 1950s at Bendix Research Laboratories, with later development under the guise of the Omni Spectra Miniature. The design was later assimilated within the MIL specifications which led to the 'SMA' designation. The SMA connector is popular and widely used. It is in fact this popularity that created the necessity for the reverse gendering of the connector interface.

The expansion of the consumer electronics market in the late 20th century led to a massive expansion in the use of SMA connectors in consumer-facing wireless products. This posed a problem for telecommunications industry regulatory bodies, who were concerned about the ease with which RF antennas could be interchanged on or within devices, potentially in breach of regulatory codes and guidance.

As SMA connectors were frequently used in antennas, there was an apparent potential for amateur wireless equipment users to connect professional-specification high gain antennas in breach of restrictions.

Effective Radiated Power (ERP) is a key measure, in part, of directional radio frequency power emitted by antennas and radio frequency transmission systems. In the US, the Federal Communications Commission (FCC) and overseas regional telecommunications regulators place restrictions or otherwise specify limits on ERP and Equivalent Isotropic Radiated Power (EIRP) for transmitters, antennas, and cable and connector assemblies.

In particular, Section 15.203 of FCC guidance mandates that products should not be designed to operate with antennas other than those provided by the original equipment manufacturer or that at least professional installation should be required.

The near-ubiquitous adoption of the SMA connector was a problem as it had the potential to facilitate amateur and consumer use of radiofrequency equipment in breach of the FCCs specified power limits. Harmful emissions from unlicensed devices could also be capable of interfering with licensed services, such as the cellular network. By reversing the genders in the RP-SMA connector, a new class of connectors was created that could limit the public's attachment of unapproved RF equipment in their wireless communications networking. They could try but would not be able to achieve a viable connection despite the appearance of a mated connection.

However, over time widespread availability and use of the Rp SMA connector, which was introduced in the 1990s, has eroded its unique status and alternate connector types may be needed to create FCC compliant devices. An example is the related RT-SMA connector, where the direction of the connector threads is reversed.

RP SMA also has a practical advantage in comparison to its SMA counterpart. Antennas usually have a male SMA antenna attached with the delicate internal pin exposed if the antenna is disconnected. Physical impacts, ingress of moisture, or grime can corrode or break the pin. Repeated matings can also impact the pin leading to a determination in radio frequency performance over time. This will lead to an awkward repair or cost of a replacement antenna. With an RP SMA male connector, the antenna will have the receptacle, which is much more resilient and a damaged cable with a female RP-SMA connector is less costly to replace than an antenna.

RP-SMA connector applications

Both SMA and RP-SMA connectors are an excellent choice of threaded connector for a range of applications operating at microwave frequencies. Whereas the standard SMA connector has proliferated in cellular/ GSM networking applications, the r-SMA connector is predominantly used in the antennas, routers, and other hardware of Wireless Local Area Networks (WLANs) in particular, the rp-sma wifi antenna. This connector is a staple component in ISM band antennas, such as the 2.4 GHz rubber duck rp-sma antenna or the rp-sma antenna 5ghz. It also features in devices and r-sma antenna units for:

Due to its prevalence in consumer wireless networking products, antennas that use this connector can be swapped out and replaced with a different WLAN antenna. Also, an rp sma antenna extension cable can be used to connect an rp-sma antenna outdoor for WiFi coverage. In recent times the market in high specification recreational drones and quadcopters has necessitated the use of various types of rpsma antenna in a range of custom assemblies. There is also consumer demand for a range of reverse sma adapter assemblies that feature this connector.

RP-SMA vs SMA

Here is a quick summary of the key comparative points for sma or rp sma connectors.

 

SMA

Reverse polarity SMA

Similarities

Sub-miniature connector

36 thread per inch

Screw-on coupling with 5/16 hex nut

Male connector threads are internalized

Female connector threads are externalized

50-ohm impedance

Rated for 500 matings

Differences

  • The male mating interface has a pin.
  • The female mating interface has a receptacle.

 

Predominantly used in cellular/ GSM applications.

  • The male mating interface has a receptacle
  • The female mating interface has a pin

 

Mainly used in WiFi and other wireless networking applications particularly the reverse sma antenna.

Frequently asked questions

What should I be looking for when choosing a radio frequency connector?

Your choice of connector is critical to the performance of your radio frequency system. SMA rp connectors vary in quality and performance among manufacturers so it is essential to make a discerning selection. Many antennas rely solely on a single connector as the point of mechanical and electrical connection and a poor connector selection is a common cause of sub-optimal antenna performance.

Here are some key considerations:

  • Crimped vs soldered connector. Crimping is a more reliable method of securing a connector to coax cable. The connections made tend to be stronger and more reliable. Solder can be chipped away or broken off.
  • Materials and fabrication. There can be significant variation in the quality of materials and manufacturing used to make RP SMA connectors, despite standardized dimensions and specifications. Key components like bulkheads can vary significantly in thickness. Data Alliance carries RP-SMA female connectors with a bulkhead that is 3.5mm thick, compared to the thinner and less durable 2mm bulkhead commonly found.
  • Quality of plated finishes. Plated finishes on the connector like nickel-silver or gold will protect it against environmental exposures and corrosion. Black chrome is a special coating on connectors that provides low reflectivity, which may be advantageous in some settings.

What kinds of adapters and cable assemblies are available that feature the RP SMA connector?

There is a wide range of sma reverse polarity adapter options that facilitate the maximum utility of this connector in radio frequency setups. In particular, they can be used as a wifi antenna adapter, which typically allows an RP SMA male connector antenna to be connected via a range of alternative connectors. Some example adapter types are shared further down.

An SMA connector can be directly converted to accommodate an RP-SMA cable with an rp sma adapter. These are sma female to rp sma male or vice versa and simply screw on to the existing connector. Most sma reverse polarity adapter selections deliver a decent low-noise connection which is more than adequate for attaching an

rp-sma male antenna or other peripherals.

Other types of R-SMA adapters include:

  • u fl to rp smapigtails of varying length allow easy connection of RP SMA antennas to a PCB mounted U.FL connector.
  • mmcx to rp-smacable assemblies allow mounting of an antenna further away from printed circuit boards where the micro-miniature coaxial connector attaches.
  • rp sma to n malepigtail adapters are rp-sma to n-type adapter assemblies that can be used for conversion between RP-SMA and N-type connectors in PCI cards, routers, and wireless access points.

An rp sma splitter or T adapter can be used to distribute signals to two antennas from one coaxial cable.

Which coaxial cable is suitable for the RP SMA connector?

The connector should have dimensional similarity to the connector it will be attached to. This keeps any irregularities in impedance to a minimum. Compatible coaxial cable types and gauges for the RP SMA connector include:

  • RG58
  • RG55
  • RG142
  • RG141
  • LMR-195

The reverse polarity SMA connector can be clamped or soldered on using the steps outlined below. Complete assemblies should have low rp-sma extension cable signal loss.

How do I attach a reverse polarity SMA connector to coaxial cable?

RP-SMA connectors can be used to terminate coaxial cable by either soldering or crimping application. Always ensure that you have the correct

  • connector type,
  • gender of the connector,
  • and polarity of the connector

before commencing the termination of your coax. The principles of attaching an RP-SMA connector to coax cable are similar to attaching an SMA connector but as explained above the inner genders are reversed.

Preparing your coaxial cable

To attach the connector, the coax cable will need to be stripped down to expose the inner conductor. This can be done with a three-blade coaxial cable stripper, which cuts three notches into the cable at varying depths and can be adjusted with an Allen key for the correct alignment for your cable.

This enables ready stripping of the terminus of the cable of its outer jacket and shielding layers, leaving the inner dielectric and connector.

The plastic dielectric can be carefully cut away to expose the length of conductor needed for the connector's center pin.

Attaching the center pin of a female RP-SMA connector.

The crimp ferrule and any sleeving for the finished cable assembly should be threaded on to the cable before the pin and connector are attached.

For a female RP-SMA connector, the inner pin can be either soldered or crimped into place over the conductor wire. It is essential that the conductor wire is cut down to the tip length. Dry assembly beforehand ensures that your final assembly is feasible.

  • To crimp: feed the cable's conductor wire into the center pin. Push the pin into a crimping tool and crimp down.
  • To solder: apply a little flux to the tip of your connector and apply a small amount of solder to the connector wire tip. Fit the pin over the connector wire, slide down, and apply heat with a clean soldering iron. Alternatively, solder can be applied through a small hole on the pin. Once cool check that the pin is firmly attached. Any excess solder can be removed with a sharp blade.

Once the pin is secure, the connector sleeve can be threaded on. Once in place, the connector can be secured in place by crimping with a hex crimp or soldering at its base to ensure a solid electrical and mechanical connection. When properly assembled they are weatherproof coaxial cable connectors. The connectors may also be additionally protected against humidity and cold with heat sharing sleeving over the assembly.

A similar technique also applies to attach the male RP-SMA connector.

In conclusion

The reverse polarity SMA connector will almost certainly be encountered if you are dealing with WiFi antennas and other wireless networking equipment. Though the RP SMA design was originally implemented to prevent amateur interference with wireless antennas, it has now become a widely available and versatile connector sub-class. A failure to properly identify and gender this connector type is a key cause of presumed antenna failure, so it is important to carefully work out the RP SMA connector or rp sma extension cable needed for your specific setup prior to ordering. Simply remember that it is the location of the male pin that will have swapped over to the female interface. These connectors can be attached to compatible coax with crimping or soldering or pre-assembled coaxial cables of a suitable length may be preferred.

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