What is a Coaxial Antenna?

Coaxial cable refers to a cable with two concentric conductors, and the conductor and the shield layer share the same axis. The most common coaxial cable consists of a copper wire conductor isolated by an insulating material. On the outside of the inner insulating material is another layer of ring conductor and its insulator. Then the entire cable is covered by a sheath of polyvinyl chloride or Teflon material. ^[1] .

The development of coaxial cables is mainly divided into four generations: the first generation was the use of polyethylene as a solid core insulation medium in the mid-19th century; the second generation was the use of chemically foamed PE material as an insulation medium; the third generation was the core core Porous PE material is used as the insulating medium; the fourth generation is the use of physical foamed PE material as the insulating medium. Coaxial cables can be classified according to their structure: leaky coaxial cables, multi-core coaxial cables, reduced diameter coaxial cables, and composite coaxial cables ^[3]

China's sustained and rapid economic growth

Coaxial cables can be divided into two basic types, baseband coaxial cables and broadband coaxial cables ^[6]

Coaxial cable is divided into four layers from the inside to the outside: the center

The advantage of coaxial cables is that

Coaxial cables use hard copper wires as the core and are covered with a layer of insulating material. This layer of insulating material is surrounded by a densely woven mesh conductor, which is covered with a layer of protective material. There are two widely used coaxial cables. One is a 50 ohm cable for digital transmission. Since it is mostly used for baseband transmission, it is also called a baseband coaxial cable; the other is a 75 ohm cable for analog transmission, that is, a broadband coaxial cable. This distinction is caused by historical reasons, not technical reasons or manufacturers ^[9]

Coaxial cables are usually installed between the devices. A connector is provided at each user location to provide an interface for the user. The installation method of the interface is as follows ^[10]

Electrical parameters

(1) The characteristic impedance of the coaxial cable: The average characteristic impedance of the coaxial cable is 50 ± 2, and the periodic variation of the impedance along a single coaxial cable is a sine wave, the average value of the center is ± 3, and the length is less than 2 meters ^11]

1.Check the integrity of the insulation medium

Standard coaxial cable has a round cross section

In cable television transmission, coaxial cables have been widely used in small and medium transmission systems due to their low cost and easy construction. Especially in HFC (Hybrid Fiber-Coaxial, hybrid fiber coaxial cable) network "last 1 km" transmission, can not be replaced with other cables. Many passive devices, active devices, and users require cable connections, and all devices connected with coaxial cables need to achieve impedance matching. If they do not match, the signal will be reflected between the component and the cable, increasing the impact of noise and ghosting on the transmitted image. The cables of the same specifications produced by different manufacturers on the market are very different in quality. However, as long as the cables produced by regular manufacturers are selected (the price is high), their raw materials, electrical properties, and production processes can be guaranteed, and the quality is trustworthy ^[13] .