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Antennas with RP-SMA connector

RP-SMA Antennas

Since the late 1990s, RP-SMA has become a far popular connector than SMA, and as a result of this, there are far more RP SMA antenna options than SMA antenna options.

An RP-SMA antenna is a radio frequency antenna which has a reverse polarity SMA connector attached to it as the primary means of connecting it to a radio frequency circuit. This connection will enable the antenna to either emit or receive electromagnetic energy according to its design and specifications. The connection may be direct, as in the case of attachment of an rp-sma WiFi antenna to a router or access point or indirect; via an RP SMA extension cable or RP SMA adapter to a circuit board or alternate connector type.

Antennas with RP-SMA connectors are commonly seen on WiFi, LTE 4G, GSM 3G, and Bluetooth devices. Standard SMA connectors were used on WiFi devices for decades, with the problem that non-compatible SMA antennas and coaxial antenna cables were common on the market. The FCC mandated that WIFi devices feature a different connector assembly, one not compatible with off-brand antennas and coax cables. The RP-SMA antenna was developed to address this mandate by simply reversing which gender has the pin, and which gender has the receptacle.

Data Alliance provides weatherproof / waterproof RP SMA antennas suitable for long-term outdoor use.

An RP-SMA male antenna can be attached directly to the wireless device, or extended via a coax RP-SMA cable. The connection is rated for up to 500 uses, assuming manufacturer-recommended torque.

The male connector features a 7.67mm hex barrel with interior threading at 36 threads per inch, just like standard SMA. However, the male connector features the receptacle, not the pin. The female connector has exterior threading but features the pin instead of the receptacle. Housings can be constructed from brass or stainless steel, with nickel or gold plating on the connection points and polytetrafluoroethylene (PTFE) dielectric insulation.

Like the SMA, RP-SMA WiFi antenna connectors pull DC from 0GHm to 18GHz at 50 Ohms impedance.

About the RP SMA connector.

The RP-SMA connector is a specific class of radio frequency connector which is:

  • semi-precision
  • sub-miniature
  • and reverse polarity.

It is an alternate version of the standard polarity SMA connector. SMA stands for Sub Miniature class A and is a widely used type of connector for antennas and other RF equipment.

Physical description of the rp-sma antenna connector.

Though it may look like a household 75-ohm type F cable connector it is markedly different and cannot be connected to them. They are manufactured to precise US Military specifications such as MIL-STD-348. Both RP SMA and SMA connectors consist of:

  • an outer housing with a 5/16 inch hex nut.
  • 36 threads per inch threaded barrel of ¼ inch diameter
  • An inner, gendered mating interface consisting of a connector surrounded by a PTFE dielectric.

Connector gender.

The connector is made up of male plug and female jack connectors. In reverse polarity SMA connectors, the gender of the inner pin is swapped from that of a conventional SMA connector. This means that:

  • The female jack consists of a body with its threads on the outside and an inner mating interface which carries a pin. The pin is usually found on a male standard SMA connector.
  • The male plug has internal threads for making its screw connection. The mating interface of the rp-sma male carries a receptacle rather than a pin.

Inner gender reversal of the rp-sma connector.

This reversal is an important feature as both RP SMA and SMA connectors look identical when viewed externally. However, the reversal of polarity refers to the inner gender of the connector. Indeed, both types of connectors can make an interchangeable mechanical connection, but not an electrical one. Mating RP SMA to an SMA connector will either produce two pins or two receptacles, which cannot transmit signals. More on this below.

Electrical profile of the RP-SMA connector.

These connectors have a 50-ohm impedance in keeping with the antennas to which they are attached. They are able to handle signal frequencies up to 18 GHz via semi-rigid coaxial cable or 12.4 GHz if paired with flexible coax. Loss is low with radiofrequency leakage of -90 dB at between 2 and 3 GHz.The type of cable or antenna used with this connector will determine the voltage rating for the rp-sma connector which can be up to a maximum of 500 volts.

Its VSWR also varies with assembly, typically ranging 1.05 and 1.25. The contact resistance is 2.0 milliohms and the PTFE dielectric resistance is 5000 megaohms.

Types of rp-sma antennas

The RP SMA connector is found on a broad range of antennas, typically those used in enterprise or domestic wireless networking applications including WiFi. They operate at a range of frequencies and may be dual or multi-band. These antennas may be indoor or outdoor antennas and are broadly grouped according to their physical characteristics or directivity. Here are the main groups of RP-SMA antenna.

[A] Omni-directional RP SMA antennas

Omnidirectional antennas are able to send or receive radio frequency signals of equal strength in all directions surrounding the longitudinal axis of the antenna. The signal strength is weakest at the top and bottom of these antennas, producing characteristic circular 2 dimensional or doughnut-shaped 3-dimensional antenna patterns. Because the signal is radiated through 360 degrees on the horizontal plane, increasing the gain of these antennas within the legal power limits may be difficult. However, narrowing of their beamwidth can be used to achieve suitable results if signal strength needs to be increased. Omni antennas with an RP SMA connector can be used in either indoor or outdoor wireless networking applications. They come in a variety of designs, some of which are included below, which further define the use and capabilities.

[B] Directional rp-sma antennas

Also known as beam antennas, these radio frequency antennas will transmit and receive the majority of radiofrequency energy in a specific direction. These high gain rp-sma antennas when optimally positioned and properly installed can achieve high-quality signal transmission over a significant distance, with less interference than omnidirectional antennas. We explore more on their uses below.

[C] Puck r-sma antennas

Puck antennas are named after their flattened disc-like cylindrical appearance, with a radome shaped much like a hockey puck. They are typically robust and hardwearing. Puck antennas can vary in type, frequency, and specification but facilitate a range of mounting options including through-hole, magnetic mounting, and surface mounting.

[D] Rp-sma whip antennas

Whip antennas are a type of monopole antenna, made from a length of flexible wire connected to a transceiver. Its flexibility gives it a whip-like motion when moved and makes it very resilient. The length of these antennas will vary with the wavelength of radio waves it is used with. They are often mounted on vehicles and have a wide variety of applications including use in cordless phones and other WiFi-enabled devices.

[E] Rubber duck reverse-SMA antennas

Rubber duck antennas are named because of their bulbous base and springy movement. They are a variant of the whip antenna and are typically omnidirectional. Rubber ducky antennas consist of a wire helix covered in a plastic or rubber jacket. They are a popular choice for mobile devices.

[F] Panel antennas with RP-SMA connector

Discrete panel antennas can be used both indoors and outdoors and comprise a dipole antenna and a flat reflector.

[G] Sector rp-sma antenna

A sector antenna is named because its maximum radiation has a distinct sector coverage. These antennas have a wedge or sector-shaped 2D radiation pattern. They are often used for base stations as multiple units can be combined to provide specific areas of coverage.

[H] Yagi antenna with r-sma connector

The classic Yagi-Uda antenna is a Japanese designed directional antenna which is made up of multiple parasitic dipole elements arranged in parallel and an rp-sma connector attached to its transmission line.

Why is an r sma antenna important?

The RP-SMA connector is the connector for a wide variety of antennas, in keeping with its use in wireless networking applications. In particular, the RP-SMA antenna is likely to be found on WiFi antennas which may be selected or exchanged for improvements in performance. They are also increasingly used in radio frequency circuits and antennas of drones. RP-SMA antennas can also be used for:

  • GPS
  • GSM
  • ISM bands
  • Bluetooth
  • LTE

The deliberate reversal of the gender of the mating interfaces of reverse polarity SMA connectors was designed in the late 1990s to prevent consumer or public handling of wireless networking equipment, in particular, the connection of alternate antennas to wireless equipment. This was done to comply with the US Federal Communications Commission rules on antennas. These rules stipulate that wireless equipment should not be easily altered, to prevent the connection of powerful high gain antennas by the public that might cause interference with regulated bands.

When the rp-sma connector was first manufactured its availability was limited and its unique design was widely known. This meant that anyone attempting to connect radio frequency equipment via this connector would be likely to assume that the connector was a standard SMA connector, and fail to achieve the inner mating needed for a viable electrical connection.

The choice of radio frequency connector in antenna designs matters.

Connections are often a point of structural vulnerability in all designs. The antenna connector is a frequent cause of product failure for antennas and therefore should be selected and integrated into the antennas structure in a considered manner. Often the connector is an afterthought and the only point of mechanical connection and support. Poor design with inadequate stability around the connector will lead to physical damage to the antenna and impaired electrical performance with signal failure and data losses.

Advantages of using the rp-sma connector in antennas

Today the RP SMA connector has become widely available, meaning that wireless networks can be created and altered using antennas and cables that carry this connector. Connector selection for antennas is important as the antenna will rely on the connector for both a physical and electrical connection. Its 18 GHz frequency limit covers most of the commonly used operating frequencies, and as it is small it can be used in devices where space or compactness is a concern. Like the SMA connector, the RP SMA connector is rated for up to 500 mating cycles, meaning it can be repeatedly connected and disconnected with confidence. The mated connection is moisture resistant making this connector suitable for outdoor use with appropriate protection. There is an additional physical advantage to using the rp-sma male connector at the base of antennas. Because it carries a receptacle rather than a pin, the potential for damage when the antenna is disconnected is lessened.

Considerations on selecting an antenna with an rp-sma connector

Intended use of your rp-sma antenna:  Your choice of rp-sma antenna should be guided by where and how you intend to use it. The RP SMA connector is often used in settings where the antenna will not need to be repeatedly disconnected and reconnected, for example, a domestic or office-based indoor WiFi network. The RP-SMA connector also has efficacy in outdoor wireless networking installations, due to its connection being weatherproof when properly mated.

However, rugged or extreme environments such as those encountered by the military or emergency services are likely to necessitate the use of a larger and more hard-wearing antenna connector class that supports rapid deployment.

The connection of the antenna to the R-SMA connector.  The RP-SMA antenna connector will be attached to the antenna by either soldering or crimping. Soldering provides a superior physical connection between the antenna's conductor and the RP SMA center pin or receptacle. Soldering the antenna's ground shield to the shank of an integrated antenna also improves mechanical and electrical resilience over crimping and tends to be long-lasting.

Materials and fabrication of the r-sma antenna connector.  The antenna connector itself should have a decent shank for its soldered or crimped connection to the antenna. Metals used should be compatible and minimize structural or electrical discontinuities with the antenna. The plating of the connector with materials such as gold or nickel will help the connector withstand environmental exposures that might degrade it.

Concealed or recessed antenna connectors.   Some RP SMA antenna designs have recessed or embedded connectors that are housed within the outer structure of the antenna. This may be of advantage when space for the antenna is limited and affords integration of the antenna into compact spaces on vehicles, machines, and devices. Recessed rp-sma antenna connectors that are covered by the antenna radome, can provide additional protection of the antenna connection from moisture ingress or environmental exposure.

Antenna cables:  Some rp-sma connectors are attached to a length of integrated antenna cables and connectors rather than directly to the antenna radome. This is often used where that antenna is installed at a distance from the rest of the RF system. In cabled antennas, the reverse sma cable will need to be able to rotate to prevent twisting of the attached cable while it is tightened. Rotating RP SMA connectors have an additional outer shell that provides independent rotation of the connector.

Angled and articulation of rp-sma antenna connectors:  45 and 90 degree right angled RP SMA connectors may be used in antennas to enable them to be installed at right angles to their connection point. Depending on specifications and design, these angled connectors can be affected by insertion losses and reflections along with an unfavorably high VSWR.

Many WiFi antennas, particularly those on routers, feature articulating or rotating parts. These connectors typically are attached to a wire that passes through the articulating joint of the antenna. This knuckle is often poorly sealed and a point of vulnerability to wearing, exposure, and moisture ingress.

Frequently asked questions

How can I connect an rp-sma antenna to an SMA extension cable?

Trying to attach an RP-SMA antenna to an SMA connector is a common mistake. SMA antenna connectors and their reverse polarity counterparts are incompatible and you will be unable to achieve an electrical connection. If you still want to use an SMA cable you will need to purchase an SMA to reverse polarity SMA adapter of the correct gender to convert the antenna connector so it can accommodate the cable. They are usually either:

  • RP SMA male to SMA female adapters.
  • RP SMA female to SMA male adapters.

Simply screw the adapter into the rp-sma connector and then connect the antenna extension cable.

I want to connect an rp-sma antenna to a u.fl connector. How can I achieve this?

Again adapters can be used to achieve a suitable connection to different antenna connectors including micro-miniature connectors like Hirose's U.FL or MMCX connectors. These tiny radio frequency connectors are often PCB mounted, fragile to handle, and difficult to mate. Attachment of a pigtail u.fl to rp-sma adapter is useful as the antenna can be connected at a distance via the reverse sma adapter.

How do I protect an outdoor antenna connection?

Although the RP SMA connector is a weatherproof coax cable connector, the connection can be a weak point in an outdoor antenna setup. Extremes of temperature can affect the performance of your assembly and any moisture ingress will eventually corrode not only the connector but the antenna and cable too. It is best to protect outdoor antenna installations by covering them with weatherproof coax seal tape that seals and shields the connection from the outside environment. The stretchy coax seal tape is applied by wrapping around the connection and cabling under tension and molding it down for a good seal.

Should I tighten an RP SMA connector with my hands?

Hand tightening is an unreliable method of mating rp-sma connectors. Over-tightening can badly damage the mating interface of these connectors by crushing the insulator and pin. Under-tightening potentially leaves a gap between the inner insulator surfaces that causes discontinuity and alteration of impedance and VSWR. The inner conductor and receptacle may not be adequately coupled.

For an rp sma antenna connector to be properly connected, it must be tightened with the appropriate torque. This can be done by using an SMA wrench at the hex nut on the male rp-sma connector. Wrenches can be either open box or torque radiofrequency wrenches. The wrench should be held towards the end of the handle with force applied perpendicularly to the handle. Tightening should be stopped when the break point is reached. To stop the cable assembly rotating a second wrench may need to be used to hold the assembly in place while the tightening is performed.

In conclusion

RP-SMA is a connector of choice for a range of radiofrequency antennas that operate in a variety of indoor and outdoor settings. Now the rp-sma connector is now in wide circulation, they can be readily connected to radiofrequency devices that have a compatible connector. This small connector provides a convenient means of attachment for customization of WiFi and other wireless networking setups, due to its secure connection and the high number of mating cycles it offers. Rp SMA antennas can also be connected via adapters and rp sma extension cabling to routers, wireless access points, and circuit boards for increased scope for their deployment.

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