Type N. Type BNC. Type MMBX

Image Credit: Aeroflec | TE Connectivity | Huber + Suhner 

Radio frequency (RF) and microwave connectors are used to connect the ends of cables in systems that operate in the radio frequency or microwave spectrum. Microwave refers to electromagnetic energy with a frequency higher than 1 gigahertz and a wavelength shorter than 30 centimeters. Radio frequency refers to alternating current which generates an electromagnetic field suitable for wireless broadcasting and/or communications if the current is input to an antenna. An RF connector can be found in transmission systems and allows for the coupling or uncoupling of system components. A mated pair consists of a plug and a jack.

Connector Classifications

There are three basic ways to categorize RF connectors:

• Cable connectors include plugs and jacks which terminate cables.
• Receptacles include plugs and jacks which terminate to printed circuit boards.
• Equipment chassis and adapters are used to join multiple incompatible units in, or between, series.

They include threaded or bayonet-style couplings that snap, screw, or push into place.

Bayonet - style coupling.

Image Credit: SPI

Types of RF and Microwave Connectors

There are many types of RF and microwave connectors. Please see the tables below.

MMCX. Image Credit: Samtec

Micro- miniature RF and microwave connectors

SMA. MCX. SSMB

Image Credit: AerFlex | Digi-Key | Radiall

Sub-miniature RF and microwave connectors

BNC Connector. TNC Connector. MHV Connector

Image Credit: TE Connectivity | Digi-Key | Huber + Suhner

Minature RF and microwave connectors

Type N. 2.4 connector. 7-16 connector

Image Credit: AeroFlex | AeroFlex | Digi-Key

Standard RF and microwave connectors

FME connector. Twinax connector. Type C

Image Credit: Comtelco | TE connectivity | Radiall

Other common types of RF and microwave connectors

Images for each type of RF and microwave connector can be found here.  

Cable Variations

RF and microwave connectors vary in terms of gender, geometry, and cable type.

Cable Type

Coaxial cables are transmissions lines consisting of two concentric conductors insulated from each other.

Conformable cable.  Flexible cable.

Image Credit: ITT | Delphi

• Semi-rigid cables - The connectors have a solid outer conductor made of aluminum or copper. Semi-ridge cables perform better, electrically, than flexible cable with an extended frequency range. The center is usually solid silver plated copper.
• Flexible - The cable has either a solid or stranded center conductor surrounded by a dielectric. A braid is woven around the dielectric. This forms the outer conductor and an additional plastic covering is placed on top. Flexible cables are able to handle the tight bending radii and physical stresses associated with moving applications.
• Conformable cables - Conformable cables have a center conductor of various types of metallic braid. Semi-ridge connectors can be used with a conformable cable and it will retain its shape once bent.

Gender

• Male connectors or plugs are often called header or free connectors. In coaxial RF connections, the plug is normally movable and usually attached to a cable. In shell-type, multiple-contact connectors, the plug contains the socket contacts and mounts on the rack or “hot” side of the system.

• Female connectors or jacks are connecting devices into which plugs are inserted to make circuit connections.

Connector gender.

Geometry

In terms of device geometry, RF and microwave connectors are either straight or right-angled. The geometry of the connector is based on the system in which it needs to fit.

Mounting Styles

There are several mounting styles for RF and microwave connectors. 

Bulkhead. PC Mount.

CableEnd. JamNut

 Aeroflex | DigiKey

Huber + Suhner | TE Connectivity

Specifications

Performance specifications for RF and microwave connectors include:

• Impedance- Impedance is a characteristic property of a transmission line describing the ratio between the electric and magnetic field. Most RF and microwave connectors provide a nominal resistance of 50 or 75 ohms (Ω). Some connector series come in both 50Ω and 75Ω. Fifty ohms connectors on 75Ω cables should be used at frequencies below 500 MHz (and vice versa). This practice is done since 50Ω connectors are generally less expensive due to their greater usage.
• Size of cable- The connector size (diameter) should match the cable diameter as closely as possible. This will help reduce reflections which hinder performance. Reflections will generally increase as a function of frequency, and smaller connectors will generally perform well at higher frequencies.

Connector diameter. Image Credit: Bixmart

• Frequency range- Frequency and cable range are the primary factors when selecting a connector. This specification helps identify the connector series used. It is recommended to use push-on or bayonet style connectors at low frequencies (below 6GHz) and threaded connectors for high performance, low noise applications.

Bayonet style connectors are used for low frequencies and threaded connectors are best for high performance.

Image Credit: Norgren | Xmultiple

• Power- Power handling is limited by the cable's power specification and is determined empirically. Higher power applications require large diameter connectors. Power handling capability will diminish as a function of frequency and altitude.
• Working voltage - Working voltage is the maximum operating voltage of the connector
• Operating temperature - Operating temperature is the full-required range of ambient operating temperature.
• Insertion loss - Insertion loss (in dB) is the total RF power transmission loss resulting from the insertion of a device in a transmission line. It is defined as the ratio of signal power at the output of the inserted device to the input signal power at the input of the inserted device.
• Voltage standing wave ratio (VSWR) - Voltage standing wave ratio (VSWR) is a unit-less ratio that ranges from one to infinity and expresses the amount of reflected energy at the input of the device. A value of one indicates that all of the energy passes through. Any other value indicates that a portion of the energy is deflected. There are many online calculators available to determine this ratio.

Features

RF and microwave connectors are available with many different features to ensure that the device fits the application.

• Moisture or oil resistant - Gaskets or seals protect the connector against moisture, oil, and other contaminants.
• Hermetically sealed - A hermetic seal is impervious to air or gas. They can also be used to protect against internal moisture.
• Hospital grade - Hospital grade connectors must conform to rigorous safety standards associated with official Hospital Grade certification. The testing for this certification includes prevention of inadvertent plug disengagement from outlets and increased shock and impact ratings.
• Environmentally resistant - Environmentally resistant connectors can be used in hazardous chemical environments.

Resources

RF & Microwave Solutions Guide