How coaxial cables work

Coaxial cable is divided into four layers from the inside to the outside: the central copper wire (single-strand solid wire or stranded wire), plastic insulator, mesh conductive layer and wire sheath. The central copper wire and the mesh-like conductive layer form a current loop. It is named because of the coaxial relationship between the central copper wire and the mesh conductive layer [6].

Coaxial cables conduct alternating current rather than direct current, which means that the direction of the current is reversed several times per second [6] .

If a normal wire is used to transmit high-frequency current, the wire acts as an antenna that emits radio outwards, and this effect loses the power of the signal and reduces the strength of the received signal [6] .

Coaxial cables are designed to solve this problem. The radio emitted by the central wire is isolated by the mesh conductive layer, and the mesh conductive layer can control the emitted radio by grounding [6].

There is also a problem with coaxial cables, that is, if a certain section of the cable is squeezed or twisted, the distance between the center wire and the mesh conductive layer is not consistent, which will cause the internal radio waves to be blocked. reflected back to the source of the signal. This effect reduces the acceptable signal power. To overcome this problem, a plastic insulator is added between the center wire and the mesh conductive layer to ensure a consistent distance between them. This also causes the cable to be relatively stiff and not easy to bend [6].

coaxial cable

coaxial cable

In essence, the shielding material of coaxial cable is mainly to improve the outer conductor, from the initial tubular outer conductor to single-layer braid and double-layer metal. Although the tubular outer conductor has very good shielding performance, it is not easy to bend and is inconvenient to use. The shielding efficiency of single-layer braiding is the worst, and the transfer impedance of double-layer braiding is 3 times lower than that of one-layer braiding. It can be seen that the shielding effect of double-layer braiding is greatly improved than that of single-layer braiding. Major coaxial cable manufacturers are constantly improving the outer conductor structure of the cable to maintain its performance