Coaxial Cables (RF)
1. Coaxial Cables Overview
RF coaxial cable (RF) is a cable designed to transmit RF signals. Its structure achieves electromagnetic shielding through the coaxial design of the inner and outer conductors and is suitable for the transmission of high-frequency signals. Due to its low loss and strong anti-interference characteristics, it is widely used in communications, radio and television, and test equipment.
2. What are the Structure and Materials of Coaxial Cables?
RF coaxial cable consists of four layers:
Inner Conductor: usually a single-core/multi-strand wire made of copper or silver-plated copper, responsible for signal transmission.
Insulation Layer: polyethylene (PE), polytetrafluoroethylene (PTFE), and other materials that wrap the inner conductor to provide electrical isolation and fix the structure.
Outer Conductor: copper mesh braid or aluminum foil, used to shield external electromagnetic interference and protect signal integrity.
Outer Sheath: PVC or weather-resistant material to prevent environmental factors (such as wear and moisture) from damaging the cable.
3. What are the Technical Characteristics of Coaxial Cables?
1) Impedance Characteristics:
50Ω: mainly used for digital signal transmission (such as base stations and test equipment).
75Ω: Commonly used in video signal transmission (such as cable TV and satellite communications).
2) Low loss: Reduce signal attenuation through high-purity conductors and optimized insulation materials.
3) Shielding Effectiveness: The outer conductor can provide a single-layer braid (95% coverage) or braid + aluminum foil (100% coverage) shielding solution.
4) Frequency Range: Covering 500 kHz to 18 GHz, suitable for a variety of RF scenarios.
4. Where are Coaxial Cables Used?
Communication System: wireless communication base station, satellite signal transmission, long-distance telephone network.
Broadcasting and Television: cable television networks (CATV) and broadcast signal distribution.
Test and Instrument: RF test equipment, laboratory high-frequency signal transmission.
Computer Network: early local area network (such as RG-58), short-distance high-speed data transmission.
5. What are the Common Types of Coaxial Cables?
1) Classification by Impedance:
RG Series: such as RG-6 (75Ω, video), RG-11 (75Ω, long distance).
Semi-rigid Cable: The outer conductor is a copper tube, which is used for high-precision RF connection.
2) Classification by Use:
Baseband Cable: Transmits digital signals (such as 50Ω coaxial cable).
Broadband Cable: Supports multi-channel analog signals (such as 75Ω cable TV cable).
6. What are the Key Parameters of Coaxial Cables?
Attenuation (Insertion Loss): Measured in dB/unit length, increases with increasing frequency.
Bending Radius: The minimum bending value that does not affect performance, affecting installation flexibility.
Propagation Speed: The ratio to the speed of light, affecting signal delay.
Voltage Standing Wave Ratio (VSWR): Characterizes the degree of signal reflection, the lower the value, the better the performance.
7. Development History of Coaxial Cables
Coaxial cable was invented by Oliver Heaviside in the 19th century and was widely used in telephone and television networks in the 20th century. Later, it gradually turned to the high-frequency RF field in competition with optical fiber.