In radio frequency (RF) systems, RF coaxial cables are primarily used to transmit RF signals and are widely used in communications, testing, and measurement fields. The shielding layer of an RF coaxial cable is a crucial structure for resisting electromagnetic interference and preventing signal leakage; its design directly affects the system's electromagnetic compatibility and signal integrity. Today, we'll mainly discuss the different shielding layer structures of RF coaxial cables.
The main function of the shielding layer in an RF coaxial cable is to block external electric and magnetic fields from entering the cable, preventing useful signals from being contaminated by noise; and to prevent internal RF signals from radiating outwards, avoiding interference with surrounding circuits. Shielding effectiveness is measured in dB; the higher the value, the stronger the anti-interference capability. RF cable shielding layers are mainly composed of conductive materials, achieving interference suppression through reflection, absorption, and current conduction. Different structures exhibit significant differences in shielding effectiveness, flexibility, cost, and frequency adaptability. Based on application scenarios and performance requirements, their structural forms are mainly divided into the following categories:
1) Single-layer braided shielding: This is the most basic structure, usually braided from tin-plated copper or bare copper wire, with a braiding density generally between 60% and 95%. It boasts excellent structural flexibility, facilitating bending and installation, and is relatively inexpensive. However, due to the presence of braided gaps, its shielding effectiveness decreases with increasing frequency, and its ability to suppress magnetic field interference is limited. This type of cable is suitable for low-interference scenarios such as indoor low-speed communication and internal wiring in testing equipment.
2) Double-layer braided shielding: A braided mesh layer is added to the single-layer base, with the two layers interlaced for more complete coverage and a braiding density exceeding 95%. Shielding effectiveness is improved to 70-90dB, with significant suppression of mid-to-high frequency interference. The double-layer structure effectively compensates for leakage from the single-layer mesh while maintaining good flexibility, making it suitable for medium-interference environments such as industrial automation, base station RF links, and vehicle communication.
3) Aluminum foil + braided composite shielding: The aluminum foil provides 100% electric field shielding, while the braided layer enhances magnetic field suppression and mechanical reliability, achieving a shielding effectiveness of 90-100dB. Aluminum foil offers excellent high-frequency interference suppression, while the braided layer enhances low-frequency and magnetic field shielding. This structure achieves a good balance between anti-interference performance and flexibility, making it the preferred choice for many communication and test/measurement applications.
4) Solid or semi-solid shielding: In applications requiring extremely high shielding effectiveness, seamless shielding layers are formed using copper tubing drawn from steel or aluminum tubing welded together. This structure completely eliminates porosity, providing near-perfect shielding effectiveness while exhibiting extremely low transfer impedance. However, the trade-off is higher cable rigidity, stricter bending radius requirements, and greater weight.
