Common antenna connectors

The basic structure of a coaxial connector includes: the center conductor (positive or negative center contact); the dielectric material outside the inner conductor, or insulator; the outermost part is the external contact, which plays the same role as the outer shield of the coaxial cable, that is, transmits signals, serves as a shield or a grounding component of the circuit. Coaxial connectors are mainly divided into: SMA, SMB, BNC, TNC, SMC, N type, BMA, etc.

1. Common sense about RF coaxial connectors

      Male: Male connector, with thread inside and needle inside, sometimes also called "J" port. Such as TNC(M)

      Female: Female connector, with threads on the outside and a hole on the inside, sometimes called the "K" port. Such as SMA(F)

      RP: Reverse Polarity means that the head and the needle inside are opposite.

      Bulkhead: It is a connector with lockable screws on the board. It includes washers, screws and retaining walls (such as SMA FEMALE BULKHEAD). It is generally used for boards.

      PCB: It is a connector with legs that can be soldered to the board. (Such as SMA FEMAL PCN).

      Panel: It is a connector with screw holes that can be locked on the board with screws. (such as SMA PANEL MOUNT) usually has 4 holes and 2 holes.

2. Describe the commonly used elements of RF connectors

      1、接头类型: SMA、SMB、BNC、TNC、SMC、N型、BMA等
      2. Characteristic impedance: 50 ohm is marked as 50 or 50 is not marked, 75 ohm is marked as 75
      3. Contact key mode: male, female
      4. Shell form: straight: no standard; curved: W
      5. Installation form: Flange: F Nut: Y Welding: H
      6. Wiring type: adapted cable model, inner diameter and outer diameter requirements, etc.
      7. Attenuation: corresponds to the signal strength attenuation caused by the passage of radio frequency signals in different frequency bands.
      8. Thread type: external thread, internal thread
      Note: Usually the connectors on the equipment side are female external threads, and the connectors on the cable side are mostly male internal threads.

3. Common transmission cable connectors

      Considering the effect of the feeder line, of course, the thicker the better. However, the thicker it is, the more expensive it will be. The price of connectors is also high, and it is difficult to handle them.It will be more troublesome. Therefore, when choosing a feeder, it is “appropriate”.

      3.1、SMA
      The SMA series connector is a widely used small threaded coaxial connector with long life, superior performance and high reliability. It is widely used in RF coaxial cables or microstrips for radio frequency loops of microwave equipment and digital communication equipment.
It is commonly used in wireless equipment for the GPS clock interface on the single board and the test port of the base station RF module. At this stage, the most common interface for handheld walkie-talkies is already very common.

      3.2、SMB
      The SMB coaxial connector is a small push-lock RF coaxial connector. It has the characteristics of small size, light weight, easy use, and excellent electrical performance. It is suitable for connecting coaxial cables in high-frequency circuits of radio equipment and electronic instruments. On wireless equipment, it is often used to connect the base station side E1 transmission cable to the base station DDF small transmission box.

      3.3、BNC
      BNC type coaxial connector is a bayonet type RF coaxial connector, which has the characteristics of fast connection and reliable contact. It is widely used in the field of radio equipment and electronic instruments to connect RF coaxial cables. Nowadays, it is used on some equipment that often needs to be replaced at any time, such as monitoring, radio, and detectors.

      3.4、TNC
      The TNC type coaxial connector is a threaded connector type radio frequency coaxial connector. It has the characteristics of wide operating frequency, reliable connection, and good earthquake resistance. It is used to connect radio frequency coaxial cables in radio equipment and instruments. It is especially suitable for mobile communication equipment under vibration conditions.

      3.5, N type
      The N-type series coaxial connector is a medium-to-high power connector with a threaded connector structure. It has the characteristics of strong shock resistance, high reliability, and excellent mechanical and electrical properties. It is widely used to connect radio frequency coaxial cables in radio equipment and instruments under vibration and harsh environmental conditions.

      Commonly used in GPS antenna feeders, RF connections of RF modules, lightning arresters, power dividers, combiners and other connectors.

      3.6、DIN
      The DIN type (also called 7/16 or L29) series coaxial connector is a larger threaded connector. It has the characteristics of firmness and stability, low loss, high working voltage, and most of them have a waterproof structure. It can be used outdoors as a connector for medium and high energy transmission, and is widely used in microwave transmission and mobile communication systems.

      Commonly used in base station antenna feeder connectors, antenna connectors, etc.

4. Some basic knowledge of antennas

      It is said that the transmission line has 50 or 75 ohms, so why?

      Hugo: For coaxial lines, we are mainly concerned with two issues: power transmission and energy attenuation during the transmission process. In order to maximize the power transmitted by a coaxial line, it is necessary to have a ratio between the inner and outer conductors of the coaxial line. For a coaxial line with air as the medium, when the outer radius/inner radius = the square root of constant E, the transmitted power is maximum, and the characteristic impedance at this time is 30Ω. When outer radius/inner radius = 3.59, this is the minimum attenuation, and the characteristic impedance at this time is 77Ω. In order to have both, the compromise value is 50Ω. Of course, 75Ω coaxial lines are now also used in some equipment, such as cable TV systems.