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SMA is the connector of choice for cellular and cellular data applications:  LTE/4G, GSM/3G;  also for GPS and HAM radio.   RP-SMA (Reverse Polarity SMA) is the connector of choice for WiFi.  We generally have more RP-SMA antenna options than SMA antenna options:  We have many SMA to RP_SMA antenna cable and adapter options that enable you to connect an RP-SMA antenna to an SMA cable or connector. .

Data Alliance offers SMA antennas for WiFi, LTE, GSM, CDMA, Bluetooth, base stations, radio astronomy, hand-held radios or telephones, machine-to-machine communications. A 433MHz antenna is also likely to be an SMA antenna.

SMA antenna and coax connectors feature 50 Ohm impedance, drawing DC from 0GHz up to 18GHz.

SMA connectors have a relatively durable screw coupling (good for 500 couplings at recommended torque) and are resistance to vibration. They are also cost-effective when designed in gold-plated brass, nickel-plated brass, or stainless steel.

The male connector features a central pin coated with nickel or gold. The barrel screws on to an SMA female antenna or coax with threading spaced at 36 threads per inch. The female connector has a central receptacle for the pin, also coated with nickel or gold, the threads external to the outer casing. Both connectors are insulated with polytetratluoroethylene (PTFE) dialectric.

An antenna with an SMA connector couples to an SMA cable:  RF coaxial antenna cable shielded to prevent signal degradation. RF coax cables cannot be stripped and soldered together without signal loss. The SMA connector is one of several RF connector designs to connect coaxial cables and antennas while preserving the signal.

Antennas with a SMA connector 

SMA antennas are a diverse group of radio frequency antennas that possess an SMA connector for attachment to a coaxial extension cable or other radio frequency hardware. An SMA connector serves as the primary channel through which radio frequency signals can flow between the antenna and the device it is attached to. These antennas are capable of intercepting electromagnetic energy and translating it into electrical current and vice versa. They are designed to connect by soldering or crimping to semi-rigid coaxial cable. This widely used and hard-wearing connector is the primary point of connection for the antenna and may even have to provide mechanical and structural support as part of an antenna's design. A single SMA connector may be installed on an antenna, or additional auxiliary SMA connectors may be present, as we discuss further on. In this case, the type or class of antenna and its applications can vary widely but the consistent feature is the SMA connector used in the antenna.

The SMA connector

The letters SMA stand for sub-miniature version A and describes the sma connector dimensions and caliber of this connector according to its original US Military (MIL) sma connector specifications, outlined in MIL-C-39012.

SubMiniature Version A (SMA) is an RF coaxial connector designed for semi-precision applications. Visually it is similar to the common household 75 Ohm Type F connector that screws into cable boxes, the design varies by 2mm and the two cables cannot b connected without an adapter.

It was developed in the 1960s by the Bendix Scintilla and Omni Spectra Corporations, both US-based engineering companies. SMA connectors are:

  • sub-miniature - a smaller radio frequency connector class designed to perform in small spaces. The male connector has a diameter of 7⁄16 inch (11 mm), and the female's diameter is 3⁄8 in (9.5 mm).
  • semi-precision - the SMA connector is designed and manufactured in line with its specification to an accuracy of 1/64th of an inch.
  • threaded - the SMA connector is coupled via a screwing mechanism with 36 threads per inch on each connector.

Additional physical features include:

  1. A male plug that has internalized threads and center pin conductor surrounded by an insulator.
  2. A smaller diameter sma female jack that has externalized screws and inner mating interface with the center receptacle.
  3. A 5/16 inch hex nut on the male, that is used to tighten the coupled connector with a special wrench.

Most antennas with an SMA connector have a male connector; antennas with an SMA female connector are very rare.  The SMA connector is coupled to its complementary part by screwing the male part over the female. Asma connector wrench is then used to tighten the connector to the appropriate level of torque. When appropriately tightened, the connection of an SMA antenna should be waterproof, resilient against movement and vibration, and secure, being rated for up to 500 mating cycles. This makes the SMA connector an ideal termination for antennas that may be used in a range of environments. The SMA antenna connector is usually made from either brass (which may be gold or nickel-plated) or steel. The mating interface contains a copper-plated inner pin or receptacle which is surrounded by a PTFE insulator. The SMA connector also comes in a range of formats, such as right-angled and bulkhead SMA connectors which facilitate all sorts of mounting and installation arrangements for SMA antennas. On individual SMA antennas, the connector may be recessed, rotating, or articulating to increase the utility of a particular antenna. As it is small and lightweight it adds little to the weight and profile of the antenna despite being very secure.

Why are SMA antennas important?

SMA antennas are in widespread use in industry, network infrastructure, commercial and consumer use. Over the past 50 years, this versatile screw-down connector has become established as a reliable choice for secure and high-performance wireless communications, particularly in cellular networks and so SMA antennas are continually produced with this connector to meet ongoing demand and maintain compatibility with existing radio frequency hardware.

The selection of an SMA antenna is a discerning one and careful evaluation of both the antenna type and the suitability of an SMA connector will prevent device failure due to the incompatibility of the antenna or failure of the connection, especially if the connector is also the sole attachment point for the antenna. A high-quality SMA connector will help safeguard the performance and longevity of the attached antenna and prevent inopportune loss of function, which can be hazardous if the antenna is being used, for example, by the emergency services or for navigation.

It’s also important to select an RF connector that is most compatible with the antenna’s intended application. For example, an SMA connector is generally well-

The SMA connector provides not only a physical but electrical match for the antenna and downstream cabling or electronics. These microwave connectors are impedance matched and have the 50-ohm impedance necessary for most radio frequency circuits. A properly matched connector means that radio frequency signal conducted by the antenna will not be affected by step changes or discontinuities that cause reflections, multipath, and ultimately signal interference. The applications in which SMA antennas are used, typically involve microwave or sub microwave frequencies. As the SMA connector:

  • has a frequency range of DC to 18 GHz,
  • is tolerant of voltages up to 300 volts,
  • has maximum radio frequency leakage of -60 dB.

This means SMA antennas are able to handle the high frequency and high voltage applications with limited attenuation, making them well suited to the wide range of wireless applications shared below.

SMA Antenna Applications

The applications of the SMA antenna are determined largely by the applications for the SMA connector. Though initially developed for the defense, aerospace, radio astronomy, and Testing and Measurement sectors, the SMA connector has become much more prevalent in use in cellular telecommunications, radio navigation (including GPS), and wireless networking, being used often for sub-6 GHz frequencies.

Key types of SMA antennas

Knowing the typical applications of SMA antennas will inform the selection of the most appropriate type of antennas needed for effective wireless networking and communication. The key characteristics of an antenna that should be evaluated include:

  • Frequency: the portion of the radio spectrum at which the antenna becomes resonant. Some antennas operate at a specific frequency, others are multiband, which is particularly useful for cellular communication.
  • Bandwidth: the range of frequencies across which the antenna will perform as specified.
  • Directivity: whether or not the antenna radiates or receives a greater portion of electromagnetic energy in a specific direction. This usually differentiates directional SMA antennas, which focuses the electromagnetic energy in a specific direction, from omnidirectional SMA antennas, that radiate equally in all directions perpendicular to the antenna's axis.
  • Gain: essentially the antenna's use of input power to radiate electromagnetic energy.
  • Radiation pattern: also known as an antenna pattern, is a graphical two or three-dimensional representation of how an antenna radiates or receives electromagnetic energy.
  • Polarization: the orientation of the electromagnetic waves as they either radiate from or are received by an antenna. Antennas can have:

○      horizontal

○      vertical

○      elliptical

○      circular

These properties of antennas will determine how an SMA antenna can be optimally used in a wireless communication system and can be used to plan their locations and proximity to access points.

[A] Cellular SMA antennas

The SMA connector is recognized as standard output for cellular antennas. They cover the key cellular technologies including:

  • GSM: Global System for Mobile Communications, a telecommunications standard that is also known as 2G. It has worldwide coverage and is still in widespread use. Depending on the geographic region the carrier frequency will vary, usually within the 850-900 or 1800-1900 MHz bands so the antenna gsm users purchase will need to be compatible.
  • Universal Mobile Telecommunications System (UMTS): is a third-generation standard for cellular communication based on GSM that uses wideband radio access technology to provide bandwidth to operators. It also operates at a range of frequencies, notably the 850 MHz band and the 2100 MHz band (both of which are licensed), and is known to support international roaming where devices are compatible. It has largely been overtaken by 3G.
  • 3G: also known as the third generation, is a cellular telecommunication technology that superseded the 2.5G standard, providing faster data transfer rates and more secure operation. It is compliant with specifications (IMT-2000) devised by the International Telecommunication Union. The higher data transfer rates mean that in addition to voice telephony, 3G can support wireless and mobile internet access, mobile TV, and video calling. A number of standards including UMTS and CDMA2000 operate under the 3G identity.
  • LTE: also known as Long Term Evolution is a wireless broadband standard devised by the Third Generation Partnership Project (3GPP). LTE has been devised to provide a path for progression or upgrade of GSM and UTE technologies, increasing their capacity and data rates. A range of novel digital signal processing and modulation techniques are harnessed and utilizes a range of frequency bands which can lead to compatibility issues when roaming. It has some similarities to 4G but remains distinct and antenna LTE connectivity is usually achieved with paired antennas as explained below. The antenna 4g users require will need alternate frequencies.

A sma connector antenna can be used with a cellular antenna cable for cellular network infrastructure or as signal boosters, in areas where cellular coverage is poor. They are a key last-mile solution for remote areas where little cellular infrastructure is present or for temporary deployment. A sma cellular antenna can help overcome some of the limitations encountered with mobile communication including:

  • Frequent disconnection or loss of signal
  • Variable latency
  • Inconsistent speeds
  • Inability to utilize VoIP or mobile internet

Cellular antennas or cellular repeaters usually consist of an outdoor donor antenna which feeds the signal to a secondary antenna, installed indoors where coverage is required. These wideband or multiband SMA antennas can be used as vehicle-mounted cell phone signal boosters and may be single or multiband antennas depending on requirements.

[B] GPS SMA antennas

Global Navigational Satellite Systems, like the Global Positioning System, are reliant on sensitive, resonant antennas with good exposure to the open skies. This is because these radio navigation systems acquire their data from a constellation of orbiting satellites that continually broadcast time, status, and positional data. Ideally, four satellites are needed to facilitate a 'fix' on a GPS receiver. This signal is captured by a GPS antenna, amplified, and then used by GPS devices for location, tracking, and navigation functions. Due to the attenuation that occurs as the satellite signal penetrates the earth's atmosphere, a GPS signal is often weak, and further deteriorated in dense vegetation or built-up environments where reflections and multipath are common. An external GPS antenna is often more powerful than those present within devices and can assist in reducing the start-up time or Time To First Fix (TTFF) of the GPS system.

SMA connectors are a common feature on external GPS antennas, that can be optimally positioned using through-hole mounting, magnetic mounting, or extension cables. GPS antennas can also be paired via a gps antenna connector with LTE antennas for enhanced performance as we explore further on.

[C] 2.4 GHz SMA antennas

The 2.4 GHz frequency band is an unlicensed Industrial Scientific and Medical (ISM) band. It is therefore used by a wide range of wireless technologies, many of which are consumer-facing such as:

  • WiFi
  • Bluetooth
  • ZigBee

Wireless local area networking and personal area networking may require external antennas to enhance signal coverage. In contemporary domestic settings, a range of consumer products and devices use this frequency like wireless baby monitors, cordless phones, drones, closed-circuit television, printers, keyboards, headphones, and speakers. This is because certain environments, like built-up areas or inside buildings, can cause reflections, refraction, and multipath interference at this frequency. At 2.4GHz signal penetration through walls and materials like concrete can be variable. External SMA antennas can, therefore, be used to set up an optimized network that makes the most use of routers or wireless access points. A sma dual-band antenna can support both 2.4 and 5 GHz WiFi. If you are purchasing an SMA antenna for a WiFi application it is prudent to check connector compatibility as many WiFi routers utilize Reverse Polarity SMA connectors. These connectors appear similar to SMA connectors but are incompatible. More on this below.

[D] MIMO antennas with SMA connector

MIMOstands for multiple-input and multiple-output and refers to a type of spatial diversity where a radio link capacity and spectral efficiency is increased by multiplying the number of antennas transmitting and receiving a signal. This technique utilizes multiple signal paths between antennas and overall leads to faster propagation and increased throughput of data. Multipath, which is often associated with interference is used to advantage by MIMO and adds robustness to transmissions using this technique.

In MIMO, different antennas transmit the propagated spatial streams in the same frequency as the primary transmitting antenna, but with phase offsets that are known. This enables the receiver to reconstruct the original signal and recover the transmitted data.

MIMO is a feature of a number of wireless and cellular networking standards including variants of WiFi, WiMax, and LTE.

SMA antennas are frequently used for multi-antenna setups.

SMA antennas can be used to create wireless diversity schemes like antenna diversity or spatial diversity. Like MIMO, this technique uses paired antennas to enhance a wireless link. It is particularly useful in environments where line of sight between transmitting and receiving antennas is absent and rather, relies on multipath to propagate the signal. Multiple antennas transmitting and receiving on the same frequency provide several observations of the transmitted signal and increases the opportunity for it to be accurately recovered.

Frequently asked questions

Are SMA antenna connectors and RP-SMA connectors the same?

No. You will find that though SMA connectors and RP-SMA connectors may be able to be screwed together, they are unable to make an electrical connection. This is because RP-SMA or reverse polarity connectors are a distinct variant of the standard SMA connector. RP-SMA connectors have a deliberate reversal of the genders of the inner mating interface. This was originally done to prevent amateur or non-professional connection of high gain antennas to devices, in line with FCC guidance to prevent their illicit use. In reverse SMA connectors, the male pin is switched over to the female jack and the female inner receptacle is found instead on the male plug. This means that the mating interfaces of SMA and RP-SMA connectors are incompatible as you end up with either two pins or two plugs. A sma converter can be used so that an SMA antenna can be used with an RP-SMA extension cable.

What does the AUX Antenna do?

Many cellular antennas carry an SMA connector AUX output which is supplied to enable the antenna to be paired with a second identical or compatible antenna. This is done simply by attaching a high-quality SMA extension cable to join the antennas. In this arrangement, there will be a main antenna which is capable of transmitting and receiving and an auxiliary antenna which can only receive signal. As discussed above this simple diversity arrangement is necessary for LTE connectivity. A GPS antenna can also be connected to an LTE antenna for mutual signal enhancement.

Are there any certifications I should look out for when purchasing an SMA antenna?

When purchasing antennas, there are a number of certifications that can be present with your product. These should assist in providing confidence that you are buying an antenna of good quality, which is compliant with leading international safety and quality standards.

  1. REACH

REACH stands for Registration, Evaluation, Authorisation, and Restriction of Chemicals and is stringent European Union legislation that regulates the use of substances that have been deemed harmful to both human health and the environment. It has been in existence since 2007 and has had a global impact as compliance is necessary to market products within the EU. Certification is achieved by being able to demonstrate compliance to the European Chemicals Agency and show that the end-user is not being exposed to harmful substances and the action has been taken to manage and mitigate risk. Where chemical use is prohibited, alternate less harmful substances should be sought. It applies to substances used in quantities in excess of one tonne annually. Equivalent harmonized initiatives are also in operation internationally.

  1. RoHS

The Restriction of Hazardous Substances Directive is the second piece of EU law that mandates that the use of 10 key hazardous substances should be restricted in compliant electronics products. It was first enacted in 2007 and is law in each of the European Union member states. RoHS aims to reduce the harm to health and environmental damage of the large volumes of electronic waste generated worldwide. The ten substances specified are:

  • Lead
  • Diisobutyl phthalate (DIBP)
  • Cadmium
  • Hexavalent chromium
  • Polybrominated diphenyl ether (PBDE)
  • Dibutyl phthalate (DBP)
  • Polybrominated biphenyls (PBB)
  • Bis(2-ethylhexyl) phthalate (DEHP)
  • Butyl benzyl phthalate (BBP)
  • Mercury

These substances are subject to strict limits, both in antenna components and the finished device. Restricted substances should only be present in concentrations of 1000ppm or 100ppm in the case of cadmium. Like REACH, other countries have equivalent legislation that facilitates the necessary compliance of electronics products to be manufactured and shipped to the EU.

 

 

 

  1. IP Codes

 

The International Electrotechnical Commission (IEC) publishes Ingress Protection Codes, also known as IP Codes. These codes provide ratings and classification of the level of protection mechanical and electrical components like SMA connectors have from the ingress of dust dirt and moisture. After the initials 'IP,' the digits in the code pertaining to the degree of protection against solid particles and moisture. For example:

 

  • IP40 indicates that an item or component will be protected from wires or tools of a millimeter or more. The zero indicates that there is no protection against moisture ingress.
  • IP67 is a key rating for connectors as it indicates complete protection from particulate substances like dust or sand, as well as water resistance for at least 30 minutes at a depth of up to 1 meter.

In conclusion

SMA antennas are a heterogeneous group, but all benefit from the robust physical and electrical profile of the SMA connector. The use of this widespread connector makes creating networking solutions easier as connectors, adapters and coaxial cables are readily sourced and provide consistent performance. SMA antennas are particularly known for their applications within cellular networking and can be readily paired with like or alternate antenna classes for improved performance.

Learn more

 

SMA cables 2.4GHz WiFi Antennas Dual Band Antennas GSM Antennas, LTE Antennas, 4G Antennas GSM Antennas Weatherproof Wireless gear IP67 waterproof Bluetooth Antennas Magnetic Mount Antennas Combination Antennas LTE GPS WiFi Bluetooth 4G 3G