RF connectors are a small but important part of almost every RF and microwave system. They provide the physical and electrical connection between components, cables, circuit boards, antennas, test equipment, and other parts of the signal path. The right connector can help maintain signal integrity, control losses, and support reliable operation across the required frequency and power range.
Choosing between different RF connector types is not simply a matter of selecting a connector that fits mechanically. Frequency, impedance, power handling, insertion loss, return loss, environmental conditions, mating cycles, and the physical requirements of the system all need to be considered. These factors become even more important as operating frequencies increase into the microwave and mmWave ranges.
What Are RF Connectors?
RF connectors are designed to carry radio frequency signals between different parts of an electronic system. Unlike ordinary electrical connectors, they are designed with controlled electrical characteristics so that the connection does not introduce unnecessary reflections, losses, or unwanted changes to the signal.
Most RF systems use a 50-ohm impedance, although 75-ohm systems are also common in applications such as video and certain communications equipment. Maintaining the correct impedance through the connector and the rest of the signal path helps reduce signal reflections.
An RF connector normally consists of a center contact, dielectric material, outer conductor, and mechanical housing. The geometry of these elements affects the connector’s electrical performance, particularly as frequency increases.
For this reason, an RF connector should be considered part of the RF signal path rather than simply a mechanical joining device.
Understanding RF Connector Types
There are many RF connector types, each developed for particular frequency ranges, mechanical requirements, and applications. Some are designed for general-purpose RF systems, while others are intended for higher-frequency microwave or mmWave applications.
Common connector families include SMA, SMB, SMC, BNC, TNC, N-type, 2.92 mm, 2.4 mm, and 1.85 mm connectors. There are also specialized connectors designed for specific applications, including high-power systems, test equipment, PCB integration, and miniature RF assemblies.
The connector family should be selected according to the complete system requirements rather than based only on physical size.
SMA Connectors
SMA connectors are widely used across RF and microwave equipment. Their threaded coupling provides a secure connection and makes them suitable for applications where reliable mechanical retention is required.
SMA connectors are commonly found in RF modules, amplifiers, filters, test equipment, antennas, and communications equipment. Their frequency capability makes them useful across many general RF and microwave applications, although higher-frequency systems may require other connector technologies.
N-Type Connectors
N-type connectors are larger than SMA connectors and are often used where greater mechanical strength and power handling are required.
They are commonly found in antennas, base stations, RF infrastructure, wireless communications equipment, and other outdoor or higher-power applications. Their construction also makes them useful in environments where a more substantial connector interface is needed.
BNC and TNC Connectors
BNC connectors use a bayonet-style coupling mechanism and are widely recognized in test and measurement equipment.
TNC connectors use a threaded coupling mechanism and can provide improved mechanical retention compared with BNC connectors. They are used across communications, instrumentation, and other RF applications where a secure connection is required.
2.92 mm, 2.4 mm, and 1.85 mm Connectors
Higher-frequency RF and microwave systems often require connectors with carefully controlled dimensions and electrical characteristics.
The 2.92 mm connector, sometimes referred to as a K-type connector, is commonly used for microwave applications. 2.4 mm and 1.85 mm connectors extend connector technology into still higher frequency ranges and are often found in high-frequency test and measurement, research, aerospace, defense, and mmWave applications.
At these frequencies, small changes in connector geometry can have a meaningful effect on electrical performance.
Coaxial RF Connectors and Impedance
Coaxial RF connectors are commonly used with coaxial cables because the connector maintains the basic geometry of the transmission line.
A coaxial cable consists of a center conductor surrounded by a dielectric and an outer conductor. The outer conductor provides shielding while helping establish the controlled impedance required by the system.
The connector must continue this electrical structure through the transition between cable and equipment. Poorly designed or incorrectly installed connections can introduce discontinuities that result in reflections and increased signal loss.
This is why connector specifications such as return loss, VSWR, insertion loss, and impedance are important when evaluating a coaxial RF connection.
Microwave Connectors and Frequency
As frequency increases, the physical dimensions of the connector become increasingly important.
At lower RF frequencies, small mechanical variations may have a relatively limited effect on performance. At microwave frequencies, however, the wavelength becomes much shorter. Features that appear physically small can therefore influence impedance, reflections, loss, and phase behavior.
Microwave connectors are designed with these requirements in mind. Their dimensions and construction are carefully controlled to provide predictable performance across their specified frequency range.
When moving into mmWave applications, connector selection becomes even more demanding. Engineers may need to consider connector geometry, launch design, PCB material, surface finish, cable characteristics, and the transition between different transmission structures.
Key RF Connector Specifications
Selecting an RF connector requires more than checking the connector’s physical interface. Several electrical and mechanical specifications should be reviewed.
Frequency Range
The connector’s rated frequency range indicates the frequencies over which its electrical performance has been characterized.
Using a connector beyond its specified range can result in higher reflections, increased loss, or unpredictable behavior. Engineers should therefore select a connector with sufficient frequency capability for the intended application.
Impedance
Impedance must match the rest of the signal path. A mismatch between a 50-ohm system and a connector designed for a different impedance can create reflections and reduce signal transfer.
For most RF and microwave applications, maintaining a controlled 50-ohm environment is an important part of signal integrity.
Insertion Loss
Insertion loss describes the amount of signal power lost as the signal passes through the connector.
Low insertion loss becomes increasingly important at higher frequencies and in systems with multiple interconnects. Although the loss of a single connector may be small, several connectors, adapters, cables, and transitions can add together across the complete signal path.
Return Loss and VSWR
Return loss and voltage standing wave ratio, or VSWR, describe how well the connector and connected transmission line are matched.
A poor match causes part of the signal to be reflected toward the source. In sensitive RF systems, these reflections can affect gain, frequency response, power transfer, and overall system performance.
Power Handling
Power handling requirements depend on frequency, connector construction, cable type, and operating conditions.
High-power RF systems require connectors that can withstand the expected RF power without excessive heating, arcing, or electrical breakdown. The connector should therefore be evaluated as part of the complete cable and interconnect assembly.
Mechanical Considerations
Electrical performance is only part of the selection process. The connector also needs to survive the mechanical conditions of the application.
Threaded connectors may be appropriate where a secure connection is required, while quick-connect interfaces can be useful in systems that require frequent connection and disconnection.
The number of expected mating cycles is another consideration. Test and measurement equipment, for example, may see considerably more connector cycles than a connector installed inside a sealed system.
Connector size can also influence the design. Space-constrained systems may require smaller interfaces, while larger connectors may provide advantages in mechanical strength or power handling.
RF Connectors in PCB Applications
RF connectors are frequently mounted directly to printed circuit boards. These transitions require careful attention because the connector must transfer the RF signal from the connector interface into the PCB transmission line.
The PCB trace, dielectric material, ground structure, vias, connector launch, and component placement can all influence the transition.
At higher frequencies, the PCB launch can become as important as the connector itself. A connector with excellent published specifications may not deliver the expected system performance if it is poorly integrated into the board design.
For this reason, RF connector selection and PCB layout should be considered together during the design process.
RF Adapters and Interconnect Transitions
RF systems often need to connect components with different connector interfaces. Adapters can provide a practical way to connect these components without redesigning the entire system.
For example, a system may require an SMA-to-N-type connection, or a transition between a coaxial connector and another microwave interface.
However, every additional adapter introduces another interface into the signal chain. Engineers should therefore consider the frequency range, insertion loss, return loss, connector gender, and mechanical requirements before adding an adapter.
In high-frequency systems, minimizing unnecessary transitions can help reduce uncertainty and maintain signal integrity.
Environmental and Application Requirements
The operating environment can also influence the choice of RF connector.
Outdoor communications equipment may require protection against moisture, temperature changes, vibration, and other environmental conditions. Aerospace and defense systems may have additional requirements related to shock, vibration, temperature, size, weight, and reliability.
Laboratory equipment may place greater emphasis on measurement repeatability and connector mating cycles.
The correct connector is therefore the one that meets both the electrical requirements and the physical conditions of the application.
Selecting the Right RF Connector
A practical approach to connector selection starts with the signal requirements. Engineers should establish the operating frequency, impedance, expected power level, acceptable insertion loss, return loss requirements, and environmental conditions.
The mechanical interface can then be selected based on available space, cable type, mounting method, mating requirements, and expected service conditions.
It is also important to consider the connector as part of the complete interconnect. Cable assemblies, adapters, PCB transitions, and connectors all contribute to the performance of the signal path.
For demanding RF and microwave applications, reviewing these elements together can help avoid unexpected performance problems during testing and integration.
RF Connectors for Long-Term RF System Performance
The choice of RF connectors can influence much more than the physical connection between two components. Connector type, impedance, frequency capability, insertion loss, return loss, power handling, mechanical construction, and environmental requirements all contribute to the performance of the complete RF system.
Understanding the different RF connector types, coaxial RF connectors, and microwave connectors gives engineers a better basis for selecting interconnects that match the requirements of their application. At Rfiber Solutions, we help customers source RF, microwave, mmWave, and electronic components, including hard-to-find, long-lead-time, EOL, and obsolete parts. This includes the interconnect components needed to keep demanding RF systems operating reliably.