Coaxial connector

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Multimedia or satellite socket, top left and right: Belling-Lee sockets for radio and television, bottom center: F socket for data or satellite.
Foreground: female Belling-Lee connector ( coupling )

Coaxial connectors are used for the detachable connection of coaxial cables .

Like these, they are designed to be coaxial in order to obtain the advantages of coaxial cables: low electromagnetic interference and radiation as well as good electrical shielding.


Cross section of a connector

The higher the frequency of the signal, the smaller the wavelength of a signal in the cable. If the wavelength is on the order of the cable length or less, reflections can interfere with the transmission. Reflections always occur where the impedance of the transmission path changes. For a good transmission of high frequencies, the impedance should therefore have the same value over the entire route. Connectors should therefore have the same impedance as the respective cable. The impedance is therefore an important parameter of a connector for high frequency applications.

The impedance of a cylindrical connector, like the impedance of a coaxial cable, results from the ratio of the diameter of the inner conductor to the diameter of the dielectric :

where is the wave resistance of the vacuum and the relative permittivity of the dielectric. From this connection it can be seen that the inner pin of 75-ohm plugs with the same insulating material must be thinner than with 50-ohm plugs of the same size.

Further parameters are the maximum transmittable frequency, the maximum transmittable high-frequency power at a certain frequency and the insertion loss and the reflection factor .

Types of construction and use

BNC connector

BNC T-piece
Differences between BNC connectors in 50 Ω and 75 Ω

The most common coaxial connector design is the BNC connector ( Bayonet Neill Concelman ), named after the developers Paul Neill ( Bell Labs ) and Carl Concelman ( Amphenol ). They were designed as a scaled-down version of the C-connector in the late 1940s , based on a patent by Octavio Salati .

The interpretation of the abbreviation is controversial; Bayonet Navy Connector , British Naval Connector , Bayonet Nut Connector , Bayonet Naur Connector or Bayonet Norm Connector are also often mentioned .

BNC connectors are coaxial connectors with a bayonet lock for high frequencies up to around 1  GHz , sometimes up to 4 GHz, with a defined wave impedance of either 50 or 75 Ω. The 50 and 75 ohm types can be plugged together. They are mainly used in radio and video technology. Japanese and American-made home video recorders were usually equipped with BNC connectors from the late 1970s. After the SCART plug connection became established in Europe in the 1980s, only SCART and Cinch connections were built into home video recorders and the use of BNC plugs on these devices fell sharply.

The use of BNC in 10BASE2 - computer networks with RG-58 cable (50 Ω) is greatly decreased, since there twisted-pair technique has displaced the coaxial cable. As a special form, BNC connectors with a wave impedance of 93 Ω were also produced for certain network applications with RG-62 cables. BNC technology has also established itself for the transmission of weak direct currents, low-frequency alternating currents and pulses in laboratory operations, because the outer conductor shields electrical interference. The coaxial structure offers protection against external electrical fields. For this reason, the connections to measuring devices such as oscilloscopes , frequency counters and function generators are usually made using BNC technology. In the GDR, BNC connector versions were specially developed for measuring stations, which instead of a bayonet had a collar made of springy contact tongues, which could, however, be pushed onto normal BNC sockets. This allowed the measurement work to be carried out very quickly, as the plugs could be quickly plugged in. The Liechtenstein company Neutrik is pursuing a similar concept with its push-pull BNC connectors, which also prevent the connection from being loosened by pulling the cable. In order to release it, the plug must be pulled from the BNC socket on its plastic housing,

Since the bayonet connection should not contribute to the wave impedance of the system, because the external contact is made on a sleeve located under the bayonet, BNC connector variants with a bayonet lock made of plastic were also manufactured in the GDR. This made it possible to use an expensive metal-saving construction and the possibility of marking the plugs with colored plastics.

Screwable small housings with BNC connections are sold under the name Circuit box , BNC box or Shielded Box . In contrast to a tinplate housing, which has to be soldered, it can be opened and closed effortlessly with the same high-frequency properties.

TNC connector

TNC T-piece and coupling (female)

TNC connector ( English Threaded Neill Concelman ) are coaxial connectors for high frequency to about 11 GHz with a defined wave impedance of typically 50 Ω, and there are still TNC variants with 75 Ω. TNC connectors are substantially similar to BNC connectors, however, are achieved by a thread (English: thread ) held by a bayonet connected to each other. Like the N connector, TNC connectors are designed up to approx. 18 GHz. The developers Paul Neill and Carl Concelman created this standard in the late 1950s as an alternative to BNC connectors, the electrical properties of which left something to be desired in environments with strong vibration, such as vehicles, due to the relatively loose bayonet lock.

The RP-TNC ( English reverse polarity threaded Neill Concelman ) is a special form of the TNC connector. Externally, both connectors are the same, only the inner parts have been swapped - RP-TNC connectors have a socket-shaped (female), the sockets a plug-shaped (male) central contact.

Belling-Lee connectors

Antenna connection cable for radio or television as Belling-Lee or IEC-60169-2

Belling-Lee connectors ( IEC 60169-2, therefore mostly referred to in the trade as IEC plug or IEC socket) were manufactured by the English radio manufacturer Belling-Lee Ltd. around 1922. and were originally only intended for medium wave . Although, unlike more modern coaxial plugs, they are not adapted to the 75 ohm impedance of the antenna cable, Belling-Lee connectors are still used today on every television set and many radios in Europe for connecting VHF (FM) and UHF antennas as well as cable networks and antenna sockets installed in houses .

Usually, for the sockets in televisions cable with a connector is required, while for radio device a cable with a coupling is needed. Since the wall sockets are also designed accordingly, a connection cable usually has a plug at one end and a coupling at the other and therefore fits (if necessary after it has been turned) for radio and television operation as well as an extension cable.

4/13 connector

Like the UHF connector, this connector is a derivative of the banana connector. There are two variants of this connector, with a short shield in accordance with DIN 47283 and with a long shield in accordance with DIN 47284. Because of the not clearly defined wave impedance, these connectors have become uncommon in HF technology. Plugs comparable to DIN 47294 are used as DIN 19262 for PH electrodes.

Dezifix connector

The specialty of the Dezifix connector is that it is a hermaphroditic connector. This allows devices to be connected to one another directly without connecting cables in between. Cables without an adapter can also be extended with additional cables.

6 sizes are defined, which are identified with letters A – F. Sizes A and B are intended for measurement technology, B to F for operating technology. The sizes E and F are connected with screw flanges and are watertight, the other sizes with a union nut. With the type I there is also a variant of the size E for interiors, which is connected with a union nut. Sizes B to E are specified in DIN 47285 to 47288.

C connector

C connectors have a two-prong bayonet lock and are suitable for frequencies up to 11 GHz. They are suitable for large transmittable powers (400 watts at 1 GHz). There are also versions for high voltage (5 kV).

F connector

F connector

F connectors (IEC 60169-24) are coaxial connectors with screw locking for high frequencies up to around 5 GHz with a defined wave impedance of 75 Ω. They are the television antenna plugs customary in North America and the most widely used connectors worldwide in the field of satellite television , but also in the field of cable television . The F plugs are externally coded for the cable diameter by rings in the corrugation.

  • 3 rings: 4.0 mm
  • 2 rings: 5.0mm - 5.2mm
  • 1 ring: 5.8mm - 6.1mm
  • No ring: 7.0mm - 8.2mm
Assembly of an F connector

The plug shown is intended for self-assembly. It can be screwed onto the cable through an internal thread in the sleeve. To make contact with the screen, it is turned over to the outside beforehand. The picture on the right explains the processing steps for an 8 mm connector. Special pliers usually help to strip the cable. If you stick to the specified length specifications, a simple knife is sufficient. The massive conductor of the cable is also the central plug contact. Therefore, these plugs can only be used with certain cable types.

These plugs are also available in a weatherproof version. An O-ring is inserted into this as a seal, which protects the inner conductor of the cable from moisture. In addition to the aforementioned F-connectors for twisting on, crimp or compression connectors are also available. Inside is a thin metal tube that slides between the insulation and the screen when the cable is pushed in. By pressing together with appropriate crimping pliers or compression pliers, a gap is closed between the outer sleeve and the tube, so that the cable is securely fixed in the connector.

In addition to the usual F connectors for screwing, there are also so-called Quickfix F connectors that are plugged onto the commercially available threads.

FME connector

FME connector

FME connector ( English For Mobile Equipment ) are miniature connector having an electrical impedance of 50 Ω for frequencies up to 2 GHz. They are mainly used for external cell phone antennas in vehicles. By default, the female FME plug is attached to the antenna's most commonly used RG-58 cable. It is unusual that the female FME connector has a union nut with an external thread and the male connector has a rigid external part with an internal thread. This ensures that the connectors are only slightly larger in diameter than the cable used and can easily be laid through narrow cable ducts.

SMBA (FAKRA) connectors

SMBA (FAKRA) plug connectors (from Fa ch kr eis A utomobil) DIN 72594-1 and USCAR-18 were developed in 2000 by Rosenberger Hochfrequenztechnik especially for use in the automotive sector. The area of ​​application extends from simple antenna signals ( VHF with or without remote power supply , television signals ) to high-frequency signals for keyless entry systems, mobile radio and digital camera systems to GPS and telematics . The special feature is the color and mechanical coding of the different variants. The connectors can also be processed in pairs or in multiple combinations. In addition, emphasis was placed on the special requirements in the automotive sector (temperature conditions, vibrations). The connectors are all available with 50 Ω wave impedance and specified up to 6 GHz.

MCX, MMCX and SSMCX connectors

MCX connector of a GPS antenna

MCX connectors (Miniature CoaX) are small (3.5 mm diameter) coaxial connectors that were developed in 1990 and are available in 50 Ω and 75 Ω. They are designed for frequencies up to 6 GHz. Similar to SMB, they use a snap connection and are therefore very easy to use. DVB-T sticks for USB OTG , for example, use this connection instead of the much larger Belling Lee socket ("IEC socket"), but it is also used in devices for use on PCs.

MMCX connector for PCB mounting ( THT )

MMCX connectors (Micro Miniature CoaX) are very small (3 mm diameter) coaxial connectors according to DIN EN 122340. They are widely used in PCMCIA cards. They are specified up to 6 GHz and available for 50 Ω. SSMCX connectors (Super Small MCX) are approx. 30% smaller than MMCX. They are specified for frequencies up to 10 GHz.

See also the very similar U.FL connector from Hirose.

UHF or PL connectors

UHF connector

UHF connectors, also incorrectly called PL plugs (from PL = plug, or SO = socket for socket), are mainly used in less demanding applications in the shortwave range , for example in amateur radio or CB radio . It is also (still) the standard connection in the area of ​​4 m BOS radio , as is the case with many older company radios.

The connector developed as a shielded variant of the 4 mm laboratory plug (" banana plug "). That is why it is often jokingly called “banana plug with union nut” or, due to the abbreviation UHF, also referred to as “unsuitable for high frequency”. It does not have a well-defined impedance. The plug and socket have small ribs or notches to prevent rotation, but the union nut is not secured against unintentional loosening and is therefore prone to loosening due to vibration (e.g. in a motor vehicle ). Otherwise, the UHF connector is simple, robust, inexpensive and easy to handle.

N connector

N connector (male)

N connectors were developed by Paul Neill at Bell Labs in the 1940s . There are different sources for the origin of the name with the letter N : The name goes back to the first letter in Paul Neill's surname. Other sources give the origin of the English Navy Connector , as this connector was first used in the US Navy.

N connectors are coaxial connectors with screw locking , with a range of application up to 11 GHz and with a line impedance of 50 Ω or less often 75 Ω. N connectors are among the most commonly used connectors in professional high frequency technology .

DIN 7/16 connector

DIN 7/16 connectors were originally developed by the Spinner company and are named after their metric dimensions of inner conductor diameter (7 mm) and dielectric diameter (16 mm). They allow higher transmission powers (up to 1800 watts at 1 GHz) than N connectors. These connectors form is the standard for mobile - base stations .

SMA connector

SMA panel jack on a printed circuit board

SMA connectors are primarily used for applications in frequency ranges from 1 GHz to 18 / 26.5 GHz (depending on the version). SMA stands for Sub-Miniature-A. Plugs are the versions with union nuts and sockets are those with an external thread, regardless of the design of the inner conductor as a metal pin or a metal tube (see below). The pairs that can be screwed together are SMA male and SMA female. Compared to other RF - connectors SMA connectors are quite small, due to the screw yet mechanically very robust. The wave impedance is usually 50 Ω. Modern SMA plugs are specified up to 27 GHz and beyond, they are then referred to as "Super SMA". SSMA stands for Small SMA , was designed primarily for use in space and allows use up to 40 GHz.

There is a derived form for fiber optic cables called F-SMA connectors.

RP-SMA connector

RP-SMA plug with inner conductor as a metal tube

The SMA connector should not be confused with the Reverse-Polarity-SMA (RP-SMA) variant , often also referred to as Reverse-SMA (R-SMA). Reverse polarity means that the pin and hole in the screw connectors are interchanged. That means, in contrast to SMA, the inner conductor of the RP-SMA plug has the hollow tube into which the pin of the RP-SMA socket is inserted. The position of the external thread on the socket and that of the union nut on the plug are identical to SMA; When plugged in, therefore, RP-SMA connections cannot be distinguished from SMA connections. RP-SMA is often used for antenna connections on WLAN devices. The idea behind it was to make the (unauthorized) connection of external antennas to increase the range more difficult, since no suitable plugs were available at the time. The market reacted quickly, however, and plugs and adapters are now available in all variants.

WLAN antenna
with RP-SMA connector

WLAN antennas usually have an RP-SMA plug (female) for screw connection with the RP-SMA socket (male) on the WLAN router or with the RP-SMA socket on the antenna cable.

Comparison of SMA and RP-SMA

Inner conductor Outer conductor image Inner conductor Outer conductor image
on the device
hole screw Sma-einbaubuchse.jpg pen screw RP-SMA socket.jpg
to antenna
pen mother SMA connector.jpg hole mother RP-SMA connector.jpg

3.5mm plug

3.5 mm plugs are mechanically compatible with the SMA plugs, but no dielectric (Teflon, Ultem, ...) is used, as is the case with the 2.92 mm, 2.40 mm, 1.85 mm mm and 1.0 mm plugs. The 3.5 mm plugs can be used up to 33 GHz and are often used with adapters 2.40 mm to 3.5 mm instead of 2.40 mm to SMA. While SMA plugs are manufactured at low cost with higher tolerances, 3.5 mm plugs have lower manufacturing tolerances and are therefore much more expensive. Therefore, 3.5 mm plugs are designed for many mating cycles, whereas SMA plugs are only specified for very few connections. When connecting SMA plugs to 3.5 mm plugs, reflections occur because the dielectric of the SMA cable causes a jump in capacitance. In addition, the 3.5 mm plug can easily be damaged by the SMA plug with such a connection.

K connector

K connectors or 2.92 mm connectors are a further development of the SMA connector . Instead of Teflon , air is used as the dielectric, which allows use up to approx. 40 GHz.

V connector

V plugs or 1.85 mm plugs are designed for frequencies up to approx. 70 GHz. 2.40 mm plugs are mechanically compatible with the V plugs. They are a further development of the 2.92 mm or K connector .

W connector

For even higher frequencies up to 110 GHz, the W plugs or 1 mm plugs are used.

Connectors of the types SMB, SMS, SMC and SMP

SMB connector crimped to 5 mm coaxial cable

SMB stands for Sub-Miniature-B . SMB connectors are used for frequencies up to 4 GHz. In contrast to SMC connectors, they are only plugged in and not screwed. They are mainly used for internal device connections. SSMB occurs in many UMTS cards, stands for small SMB or nano-SMB or SMB nano . SMS probably stands for sub-miniature sliding . Some manufacturers also call this connector standard SMG.

SMS connectors are used in the frequency range up to 4 GHz. In contrast to SMB connectors, the SMS connectors do not have a snap lock. They are therefore mainly used on slide-in assemblies because they have relatively low insertion forces. In terms of the dimensions of the coaxial interfaces, they are constructed like the SMB and SMC connectors, e.g. B. Diameter of the inner conductor plug pin 0.48 mm… 0.53 mm, outer diameter of the plug 3.66 mm… 3.71 mm. SMS and SMB connectors can be plugged together.

SMC T-piece (male) and coupling (female)

SMC connectors are similar to the SMA connector, but the wrench size of the screw lock is smaller (screw connection has wrench size 6.35 instead of 8 mm for the SMA connector). The electrical data and dimensions of the plug-in interface as with the SMB and SMS connector.

SMP connectors are the "norm" for high-frequency connectors for a frequency range from DC to 40 GHz.
The connection is made. The connectors are mechanically very compact (connector interface: inner conductor pin nominal 0.38 mm diameter, outer diameter at the interface about 3.2 mm). The plugs are available in three versions with different insertion forces: snap-on versions "full detent" and "limited detent" and sliding version "smooth bore". Similar to SMS connectors, the sliding variant is intended for plug-in modules or printed circuit boards that are plugged onto one another. Usually, the modules to be connected only have plugs ( male ) and can only be coupled to one another by socket-socket adapter pieces ( female-female ) inserted therein . The specialty is that this three-part construction enables not only an axial, but in particular a small radial tolerance compensation, which is essential for multi-pole connections.

WICLIC connector

WICLIC socket and plug

WICLIC connectors come from Wilhelm Sihn Jr. GmbH & Co. KG (WISI). The plugs are used, among other things, in automobile telephone installations (antenna connections) and as an alternative to the F-connector for connecting Internet cable modems, where the connection is often called broadband or multimedia socket. The cable network operators NetAachen , NetCologne and MDCC Magdeburg-City-Com use WICLIC sockets and plugs.


QN connectors were developed by Radiall and Huber + Suhner. They are based on the connectors of the N series , but are only plugged in instead of screwed. When plugged in, they can be rotated 360 °. The plug is suitable up to 11 GHz and corresponds to the QLF (C) standard (Quick Lock Formula). Among other things, they are used in cellular base stations (such as Nortel S18000) because they can be installed much faster. QMA connectors are the smaller version of the QN connector. They are based on the SMA interface and can be used up to 18 GHz.


TS-9 socket from above

TS-9 connectors were developed by SMK and are used, among other things, for UMTS / LTE sticks to connect external antennas. For example, the companies ZTE, Novatel and Huawei use these in their UMTS sticks . With 2.0 mm (plug) or 2.5 mm (socket), the plugs are particularly suitable for small devices without great mechanical stress. The connectors are only plugged in. They are suitable for a frequency range of up to 3 GHz and a voltage of up to 100 V. They typically have a wave impedance of 50 Ω.

The TS-9 socket of a standard LTE stick, see photo, has a switched connection for the inner conductor. If no plug is connected, then the two visible contacts of the inner conductor are connected in the socket. The internal antenna is active. After plugging in a TS-9 connector, the internal contact is opened and the right contact of both is connected to the inner conductor of the connector. This automatically deactivates the internal antenna.


CRC-9 connectors are almost identical to TS-9 connectors. They are also used with UMTS and LTE sticks to connect the antenna. The difference is that the CRC-9 socket has an outer diameter of 2.1 mm, which is slightly smaller than the TS-9 socket


The structure of the selected connector, in particular the quality and diameter of the coaxial tube, determines the usable operating frequency range (cutoff frequency) for the application.

diameter designation Cutoff frequency
7 mm APC-7 , N 18 GHz
3.5 mm (SMA) 34 GHz
2.92 mm K 40 GHz
2.4 mm - 50 GHz
1.85 mm V 67 GHz
1.0 mm W. 110 GHz

Web links

Individual evidence

  1. Technical data sheet: TNC Connectors . Retrieved February 24, 2020 .
  2. Technical data sheet (PDF) at
  3. AUTO SERVICE PRAXIS 8/2012 , page 10, overview of FAKRA connectors in automobiles
  4. a b Type N Connectors. (PDF) Amphenol RF, accessed October 16, 2014 .
  5. Hewlett-Packard (Ed.): Coaxial & Waveguide Catalog and Microwave Measurement Handbook . Palo Alto CA 1980 (Document No. 5952-8207D [1979-80]).
  6. Guidance on using Precision Coaxial Connectors in Measurement (PDF; 12.4 MB) on
  7. SIERRA Wireless and Huawei cards: Aircard 850, 860, 870, 875, 775, 555D; Aircard 580, 595.
  8. SSMB ( Memento of the original from January 24, 2011 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. (PDF; 32 kB) on (German, English) @1@ 2Template: Webachiv / IABot /
  9. SSMB-Nano ( Memento of the original from January 17, 2011 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. on @1@ 2Template: Webachiv / IABot /
  10. Wisi on
  11. Technical data sheet TS-9 connector (PDF; 75 kB) on
  12. Difference between TS-9 and CRC-9 connectors on