Commonly Used Coaxial TNC/BNC/QMA/SMB/SMC Connectors

The named model of the RF TNC / BNC / QMA / SMB / SMC /DIN /FME connector is generally located by the internationally accepted main name model. The structural form naming models of different products should be formulated in accordance with detailed standards and specifications. How much do you know about the basics of RF connectors?

The Development of RF Coaxial Connector

RF coaxial connector development
The invention of RF and microwave coaxial connectors dates back to the 1940s during World War II. With the birth of radar and various radio communication equipment, connectors such as N and BNC first appeared.
With the development of radar, radio and microwave communication, N, C, TNC, and other series have been produced. After 1958, miniaturized products such as SMA, SMB, and SMC appeared. In 1964, the US military standard MIL-C-39012 “General Specification for Radio Frequency Coaxial Connectors” was formulated. From then on, RFC began to develop in the direction of standardization, serialization, and generalization, so the earliest development started from the military engineering department.

High frequency microwave coaxial connector

Type N, BNC and TNC wave coaxial connector

0.8 mm TNC coaxial connector

2.92 mm DIN coaxial connector

The N-type connector originated in 1942 and is named after its inventor, Paul Neill. The initial working frequency was 4GHz, and it was improved to 11GHz after the 1960s. The precision type can work up to 18GHz, and it is one of the most widely used connectors. There are two specifications of 50Ω and 75Ω, which cannot be interconnected. The inner diameter of the outer conductor is 7mm. Type N is similar to the Chinese standard L16, but the two are not compatible and require a dedicated N-L16 adapter.

1.35 mm QMA coaxial connector

1.85 coaxial SMB connector

3.5 mm FME coaxial connector

SMA coaxial connector

BNC is the earliest radio frequency coaxial connector, during World War II. Due to the urgent needs of the war, various types of shipboard and airborne electronic equipment were damaged, causing a large amount of damage to the US naval and air combat weapons to be repaired. In order to shorten the repair time, the U.S. Department of the Navy gathered some excellent researchers and engineers to invent the quick mating and separation connector BNC in a short period of time, which became a plug-in N-type connector. It is the originator of RF coaxial connectors all over the world. Commonly used in low-frequency circuits, the inner diameter of the outer conductor is 6.5mm. Similar to the Chinese standard Q9, but not fully compatible.

TNC is an acronym for Threaded Neill–Concelman. Do you see Neill-Concelman familiar? By the way, the NC of TNC is the same as the NC of BNC, that is to say, they have the same inventor. The TNC connector is a variant of the BNC connector and an improved version of the BNC, and its frequency characteristics are basically the same as those of the N-type. The TNC uses a threaded connection.

The APC/7mm connector (Amphenol Precision Connector) originated in the 1960s. Amphenol standard, non-polar, is the lowest standing wave among all connectors up to 18GHz, commonly known as “flat connector”. Commonly found in network analyzers. The inner diameter of the outer conductor is 7mm.

DIN7-16 coaxial connector

HN coaxial connector

TNC coaxial connector

BNC RF coaxial connector

The HN-type connector is a high-voltage version of the N-type connector introduced in the 1950s. It can work up to a voltage of 5kV, and its size is close to N-type, but its power capacity is larger.

N type coaxial connector

The DIN7-16 connector (Deutsche Industries Norm) is derived from the 6-16 (60Ω) connector invented by Spinner. The outer diameter of the inner conductor is 7mm, and the inner diameter of the outer conductor is 16mm, which is the connector with the best passive intermodulation (PIM) performance among all connectors. Commonly found in cellular base stations and broadcast television transmitters. Compatible with Chinese standard L29.

SMA was designed by Bendix in the late 1950s for semi-rigid coaxial cables. Its matching space is filled with polytetrafluoroethylene medium, and its structure is relatively simple. This connector was not intended to be used for a long time, let alone considered as a precision connector, so it is only a connector for common systems. But it is probably the most widely used connector in the world.

RF radio frequency connector

3.5mm connector: In the mid-1960s, the U.S. Department of Commerce established a Joint Industry Research Council (JIRC) for the standardization of small precision coaxial connectors. After efforts to propose a civilian product standard in 1972, the size of the air transmission line was reduced to 3.5mm, and the frequency under the modeless working state was extended to 36GHz. However, due to its high precision and high price, it has been hindered from being widely used as a general connector. Due to the needs of the situation, companies such as Hewlett-Packard have developed a high-precision, relatively cheap 3.5mm connector. Add a non-slotted protective cover on the outside. Rated operating frequency up to 33GHz. The 3.5mm connector is compatible with SMA and can be docked without loss. In the SMA working frequency range, the VSWR characteristics of the 3.5mm connector are similar to those of the SMA. The 3.5mm connector is especially suitable for test equipment due to its precision and good wear resistance.

The 2.92mm connector is similar to the 3.5mm connector in structure, but it is smaller, allowing the operating frequency to 46GHz, and its inner conductor size is the same as SMA at 0.05 inches (1.27mm). The 2.92mm connector was first developed by Maury Microwave (MPC-3 type). Such connectors developed by other companies include K-type, KMC-type, WMP4-type, etc.

The K-type connector was developed by Wiltron in 1983 (Wiltron was acquired by Japan’s Anritsu in 1990), and it is compatible with SMA, 3.5mm, and WSMA connectors. The heart of the K-type connector is its transition device, which uses a glass insulator to realize the rigid transition from the coaxial connector to the microstrip circuit, which ensures that the circuit will not be damaged when the connector is replaced or repaired.

The 2.4mm coaxial connector was invented by Julius Botke and Paul Watson in 1986 and is compatible with 1.85mm connectors. Also known as OS-50 type, the inner diameter of the outer conductor is 2.4mm. The successful development of the 2.4mm coaxial connector marks a new step in the development of millimeter wave connectors. A series of small coaxial connectors developed in front of it have made many improvements in structure, but the robustness and repeatability of the connectors are still not improved enough. This creates a cascade of problems with instrumentation and calibration standards, where greater alignment, robustness, and repeatability are required.

The 2.4mm connector can be used in a wide range of fields, and it is the first product with three grades: production grade, instrument grade and measurement grade.

1.85 and 1.0mm connectors; Hewlett-Packard Company of the United States is a manufacturing company engaged in electronic equipment and components, and it has been in a leading position in the development of millimeter wave connectors. At the European Microwave Conference in 1986, they introduced the 1.85mm connector for the first time, extending the working frequency to 65GHz. Later, Wittron Company (Wiltron Company was acquired by Japan’s Anritsu in 1990) was improved and announced in January 1989 that the 1.85mm (V-type) connector was used in the 360-type network analyzer, and it was compatible with the 2.4mm connector. The structural form of the V-type connector is the same as that of the K-type, but the size is smaller. It is also connected to the microwave circuit with a transition – a glass insulator whose center conductor is only 9 mils (0.23mm) in diameter.

The 1.35mm connector will be launched around 2020 by the German National Institute of Metrology, the German Federal Institute of Physics and Technology, Rohde & Schwarz, Rosenberg High Frequency Technology and SPINNER.

In the 1990s, Hewlett-Packard announced that they had successfully developed a 1.0mm connector with an inner conductor diameter of about 0.43mm (50Ω) and a maximum operating frequency of 110GHz, which is a top microwave connector.

The 0.8mm connector is currently the world’s smallest millimeter-wave top connector. The 0.8mm and 1.0mm connectors have some similarities, have similar structural dimensions, and have similar physical appearances. But the interior of the two is quite different. Although the technology of the 1.0mm connector can be used for reference, the 0.8mm connector still needs some new designs to obtain better performance.

For example, the ME7838D series broadband vector network of Anritsu Company uses a 0.8mm coaxial calibrator.