The most obvious characteristic of a connector is its physical size, other considerations include power handling and frequency range capabilities. To ensure maximum power transfer, the characteristic impedance of the connector should match the source and load. All of these characteristics, as well as the durability and cost of the connector, must be considered for each application.
The most common types of connectors used in RF applications are male and female configurations, standard and precision grades, high frequency, and in some cases high power versions:
BNC
The BNC connector is probably one of the most widely used connectors in the test and measurement world. It was developed by Bell Labs in the early 1950s and is commonly used for low power interconnects in RF test equipment such as audio and signal generators, oscilloscopes, and amplifiers. Cheaper BNCs use a bayonet retaining ring to provide a quick mating/unmating action and also prevent accidental disconnection. BNC connectors are typically designed to provide a characteristic impedance of 50 or 75 ohms, depending on the application. BNC connectors are typically rated for use in the DC – 4 GHz frequency range; however, they are rarely used above 500 MHz. While they are capable of handling 80 – 100 watts of average power up to 1 GHz, they typically do not have a maximum power rating.
TNC
The TNC connector is simply a threaded version of the BNC connector. It provides a more secure connection, thus reducing vibration issues that can occur with the BNC. The TNC will operate at higher frequencies than the BNC, and there are also high-power TNC versions available.
SMA
The SMA type connector was developed in the 1960s and has proven to be a very popular choice for low-power, high-frequency applications. It was originally intended for use with type 141 semi-rigid coaxial cable, where the center conductor was used as the center pin. Its use was later extended to flexible cables soldered to the center pin. It consists of an inner contact ring and a hexagonal clamping nut attached via a snap ring. A special wrench is used to achieve the correct torque; typically 5 lb-in. Different versions are available, such as high frequency, self-locking, and precision. The SMA is commonly used as an interconnect for RF boards, microwave filters, and attenuators, operating up to 18 GHz. The precision version extends the upper frequency limit to 26.5 GHz. While the SMA will mate with the 2.92mm/'K', 3.5mm and APC-3.
3.5mm
The 3.5mm connector is a precision connector primarily developed by Hewlett Packard (now Keysight Technologies). It is similar in design to the SMA but features an air dielectric for higher performance. These connectors perform well to 34 GHz but are typically used to 26.5 GHz. Because the 3.5mm is a precision connector it is more expensive than similar designs and therefore is typically used in calibration kits and metrology applications rather than common test and production applications.
2.4mm
This 50 GHz connector was developed by Hewlett Packard (now Keysight Technologies) in the mid 1980s and features a 4.7mm outer conductor arranged around a 2.4mm center conductor. The 2.4mm is available in three grades; general purpose, instrumentation and metrology. Because these connectors are not directly compatible with the SMA family, precision adapters are required to mate 2.4mm connectors to SMAs.
2.92mm/Type K
This connector was designed and developed by Wiltron (now Anritsu Corporation). This connector performs comparable to the 2.4mm, but is limited to a maximum frequency of 40 GHz. The "Type K" designation comes from its ability to cover all K-band frequencies.
Type N
This is one of the most commonly used RF connectors in the world today. Designed by Bell Labs in the 1940s, this high-performance connector features a threaded coupling interface and internal gaskets to keep out the elements. The Type N connector is rugged, relatively inexpensive, and the standard version is capable of operating at 11 GHz without mode. Precision versions push the upper frequency limit to 18 GHz. Commonly found on instruments such as amplifiers, directional couplers, power meters, and coaxial attenuators, this threaded, durable connector provides a very secure connection. Available in 50 and 75 ohm versions; the latter is commonly used in the cable TV industry.
Type C
The Type C connector was designed by Amphenol to handle high power applications and provide a quick mating/unmating operation. It uses a dual stud bayonet retaining ring similar to the BNC design. Over the years, the C connector has declined in popularity but is still available. The 7-16 DIN is used as a replacement in many cases due to its similar frequency and power capabilities. There is a 75 ohm version as well as an "SC" version that contains a threaded collar for a more secure connection.
7-16 Standard
This is the newest connector in the United States compared to the other connectors mentioned previously. The 7-16 DIN was developed by the Deutsches Institut fur Normung, hence the name "DIN". The numeric portion of its name refers to the size of the inner and outer conductors; the "7" represents the inner conductor outer diameter in millimeters and the "16" represents the outer conductor inner diameter in millimeters. The 7-16 uses an M29 x 1.5 threaded coupling nut. The 7-16 DIN connector was designed with low intermodulation in mind and is suitable for communications applications. Other common applications include antennas, base station connections, RF cables, satellite communications, and lightning protection systems.
EIA
The EIA series of coaxial connectors are available in EIA 7/8", EIA 1 5/8", EIA 3 1/8", EIA 4 1/2", and EIA 6 1/8" versions, all for RF applications. Designed to support foam or air dielectric cables, they consist of a body, a mounting flange with various bolt circles, and typically feature an interchangeable/removable center conductor "bullet". Due to the flexibility of their design, EIA connectors are not typically identified as male or female, as the connector can typically be configured as either. EIA connectors are used in high power applications such as directional couplers, coaxial cables, power amplifier outputs, and communication tower and antenna interconnects. The most common sizes for general test and measurement applications are the 1 5/8 and 7/8 EIA.
