The structure of the coaxial cable is composed of four parts: sheath, outer conductor layer, insulating medium layer and inner conductor. The function of each part is described below.
The sheath, that is, the outermost layer of insulation, acts as a protective layer.
The outer conductor has a dual function as a shielding layer, it can not only conduct low level through the transmission loop, but also have a shielding effect. The outer conductor usually has 3 structures.
1. Metal tubular. This structure is made of copper or aluminum tape longitudinally welded, or a seamless copper tube is extruded and drawn. This structure has the best shielding performance, but poor flexibility, and is often used in trunk cables.
2. The aluminum-plastic composite belt is longitudinally packaged and lapped. This structure has better shielding effect and low manufacturing cost, but since the outer conductor is a circular tube with a longitudinal slit, the electromagnetic wave will pass through the slit and leak.
3. The combination of woven mesh and aluminum-plastic composite tape longitudinally. It is developed from a single woven mesh structure. It has the characteristics of good flexibility, light weight and reliable joints. It adopts a reasonable composite structure, which greatly improves the shielding performance. This structure is widely used.
Insulation medium, PE material, mainly to improve anti-interference performance and prevent water and oxygen erosion.
Inner conductor, copper is the main material of the inner conductor, which can be in the following forms: annealed copper wire, annealed copper tube, copper-clad aluminum wire. Usually the inner conductor of the small cable is copper wire or copper-clad aluminum wire, while the large cable uses copper tube to reduce the weight and cost of the cable. Tie the outer conductor of the large cable, so that you can obtain a good enough bending performance.
The coaxial line is a two-conductor transmission line in structure, and can establish an electromagnetic field distribution similar to a static field on its cross section. One of the characteristics of the coaxial line is that it can be applied from the DC segment to the millimeter wave band.