RF cables are different from coaxial video cables in that they are filled with 100% polyethylene, which reduces energy loss. They can transmit relatively large frequency amplitudes and are easier to install and have a relatively simple structure compared to coaxial video cables. Due to their different functions and characteristics, RF cables have many classifications. This article will classify RF cables based on several common classification standards.
一, Classified by insulation type
1. Air insulated cable: In the insulation layer of the cable, except for a portion of the solid medium supporting the inner and outer conductors, the majority of the volume is air. Its structural feature is that it can travel from one conductor to another without passing through a dielectric layer. Air insulated cables have very low attenuation and are a commonly used structural type at ultra-high frequencies.
2. Semi air insulated cable: This structural type is an insulation type between the above two types, and its insulation is also composed of air and solid medium, but it needs to pass through a solid medium layer from one conductor to another.
3. Solid insulated cable: This type of cable is filled with solid high-frequency dielectric between the inner and outer conductors, and most soft coaxial RF cables use this insulation type.
二, Classified by cable structure
1. Symmetric RF cable
The electromagnetic field of a symmetrical RF cable circuit is open, and due to the radiation of electromagnetic energy at high frequencies, the attenuation increases and the shielding performance is poor. In addition, due to the influence of atmospheric conditions, it is usually less commonly used. Symmetric RF cables are mainly used in low RF or symmetrical feeding situations.
2. Spiral RF cable
The conductor in coaxial or symmetrical cables can sometimes be made into a spiral coil shape to increase the inductance of the cable, thereby increasing the wave impedance of the cable and delaying the transmission time of electromagnetic energy. The former is called a high impedance cable, and the latter is called a delay cable. If the density of spiral coils wound along the length direction is different, variable resistance cables can be made.
3. Coaxial RF cable
Due to the concentric position of its inner and outer conductors, electromagnetic energy is confined to the medium between them, resulting in significant advantages such as low attenuation, high shielding performance, wide frequency bandwidth, and stable performance. Usually used to transmit radio frequency energy ranging from 500 kHz to 18 GHz. At present, there are two commonly used types of RF coaxial cables: 50 Ω and 75 Ω RF coaxial cables. RF coaxial cable with characteristic impedance of 75 Ω is commonly used in cable optic networks, hence it is called cable optic cable. The transmission bandwidth can reach 1GHz, and currently the transmission bandwidth of commonly used cable optic cable is 750MHz.
三, Other classification criteria
According to the classification of insulation materials, they can be divided into plastic insulated cables, rubber insulated cables, and inorganic mineral insulated cables.
According to flexibility classification, it can be divided into flexible cables, flat flexible cables, rigid cables, etc.
According to the size of transmission power, it can be classified into low-power cables below 0.5 kilowatts, medium power cables between 0.5-5 kilowatts, and high-power cables above 5 kilowatts.
According to the characteristics of product usage, it can be classified into low attenuation, low noise, miniature, high stability phase cables, etc.
