Introduction to Common RF Connectors (2)
Time : 2022-08-19

In the last article, we introduced the SMA connector. Usually, when selecting RF connectors, the main factors are its frequency range, impedance, withstand voltage, VSWR, size, etc. Therefore, different connectors have different properties and are suitable for different scenarios.

There are several common types of RF coaxial connectors: N, SMA, L29, BNC, 2.92mm, 2.4mm, 3.5mm, 1.85mm, 1.0mm etc.

N Type Connector 

The Type N connector is a threaded medium power connector that can be rotated to lock. It was one of the first connectors capable of transmitting microwave frequency signals. It has the characteristics of high reliability, strong vibration resistance, excellent mechanical and electrical performance, etc. It is widely used in radio equipment and instruments and ground transmission systems under severe vibration and environmental conditions to connect radio frequency coaxial cables. It can be interchanged with similar products of NG type in the world.

The N-type connector is usually used in the frequency range: DC-18GHz, divided into 50Ω and 75Ω according to the characteristic impedance.

Applications: wireless, telecommunication systems, outdoor RF cables, instrumentation, waveguide transmission systems, etc.

SMA Connector

SMA connector is a widely used small coaxial connector with threaded connection. It has the characteristics of wide frequency band, excellent performance, high reliability and long life.

SMA connectors are suitable for connecting RF cables or microstrip lines in the RF circuits of microwave equipment and digital communication systems. There are two types of impedance: 50Ω and 75Ω, the general withstand voltage is 500Vrms, with the outer diameter 1.24mm and the inner diameter about 4.13mm.

SMA connectors are suitable for microwave applications in the frequency range DC-26.5GHz.

Applications: telecommunications, networking, wireless communications, testing and measuring instruments.

L29 Connector (or 7/16 connector)

L29 series RF coaxial connector is a kind of threaded coaxial connector produced in accordance with IEC169-4 and DIN47223, also known as DIN connector, or 7/16 connector.

It has the characteristics of low loss and high transmission power, and most of them have waterproof structure. It can be used outdoors as a connection for medium and high power transmission lines, and is widely used in microwave transmission and mobile communication antenna feeding systems.

The frequency can reach 8.5GHz, and the salt spray can reach up to 120 hours. It is produced in full accordance with the national standard or national military standard.

BNC Connector

BNC is another threaded connector available in 50 ohm and 75 ohm versions.

It has a maximum operating frequency of DC-12GHz.

BNC connectors are used for the transmission of radio frequency signals, including the transmission of analog or digital video signals, the connection of amateur radio equipment antennas, the connection of avionics and other electronic test equipment.

In the field of consumer electronics, BNC connectors for video signal transmission have been replaced by RCA terminals. With a simple adapter, RCA terminals can be used on devices that only have BNC connectors.

2.92mm Connector

2.92mm, that is, the inner diameter of the outer conductor is 2.92mm.

This series of RF coaxial connectors, also known as K-type connectors or SMK connectors, operates at a frequency of up to 46GHz, covering the entire 8mm frequency band.

Drawing on the advantages of air transmission lines, it has low VSWR and low insertion loss. Its structure is similar to that of 3.5mm/SMA connector, but faster the frequency band and smaller the size. It is one of the most popular millimeter wave connectors in the world.

With the positioning of China’s millimeter wave coaxial technology in military test instruments, 2.92mm coaxial connectors have been widely used in radar engineering, electronic countermeasures, satellite communications, test instruments and other fields. The 2.92mm connector is compatible with SMA and 3.5mm connectors. It performs well in the 46GHz band, and lower cost than 3.5mm connectors. Besides, it outperforms SMA connectors when used below 18GHz.

2.4mm Connector

2.4mm is the outer conductor diameter size of this coaxial threaded connector. It is compatible with 1.85mm connectors.

It is a connector for 50 GHz. Since there are not as many manufacturers of 2.4mm connectors as K-type connectors, the price is comparatively high. So the application is not as widespread as K-type connectors.

Applications: Precision measurement, millimeter wave communication systems.

3.5mm Connector

3.5mm coaxial threaded connector, 3.5mm is the inner diameter of the outer conductor, and the characteristic impedance is 50Ω.

Compatible with SMA, 2.92 series connectors, it usually operates up to 34GHz.

It is characterized by small size, light weight, high frequency, precision, good wear resistance, excellent electrical properties and strong reliability.

Application: widely used in the field of precision measurement, millimeter wave communication system.

1.85m Connector

1.85mm coaxial threaded connector with 1.85mm inner diameter of its outer conductor. Compatible with 2.4mm connectors, support operating frequency up to 65GHz.

In recent years, 1.85mm connectors have been optimized to reach 67 GHz frequency.

1.0mm Connector

1.0mm is the coaxial threaded connector, and 1mm is the inner diameter of the outer conductor. The 1.0 mm connector is designed to support all transmissions up to 110 GHz, an important achievement in precision manufacturing for reliable and flexible interconnects.


Operation instruction

As one of the precision instruments, RF coaxial connectors should be used properly, not only to prolong its service life, but also to bring convenience to subsequent connection use.

1. Do not use pliers to fix the RF connectors.

2. Follow the barrel principle and use connectors and cables that meet the test requirements.

3. Do not use the adapter in calibration for normal testing.

4. Follow the proper operation posture.

When unplugging the test cable assembly from the instrument, be sure to hold it on the connector. Don’t grasp the cable root to pull out, so it is easy to cause the cable and the connector connection failure.

5. Put a protective cap on the adapter. Those with external threads, such as N-Female and SMA-Female, are easily worn out. Especially the SMA-Female connector, if accidentally dropped on the ground, the thread is easily deformed. Therefore, it is best to put a plastic protective cap on the connector after use, and it can also play a role in dust prevention.

6. Pay attention to the cleaning of the RF connector, use a cotton swab dipped in alcohol to clean the connector. But do not use a cotton swab to clean the inner conductor of the air medium connector, such as 3.5mm and 2.92mm, etc.