Shielding is to ensure the transmission performance of the system in an environment with electromagnetic interference. The anti-interference performance here should include two aspects, namely the ability to resist external electromagnetic interference and the ability of the system itself to radiate electromagnetic interference to the outside. Theoretically, covering cables and connectors with a layer of metal shielding can effectively filter out unnecessary electromagnetic waves (this is also the method used by most shielding systems). However, the effectiveness of this method is limited.
For a shielding system, it is not enough to have a metal shielding layer alone. More importantly, the shielding layer must be completely and well grounded, so that the interference current can be effectively introduced into the earth. However, during actual construction, the shielding system has some difficulties that cannot be ignored: due to the strict requirements for grounding of the shielding system, it is very easy to cause poor grounding, such as excessive grounding resistance, unbalanced grounding potential, etc., so that at certain two points of the transmission system A potential difference will be generated between them, which will generate a current on the metal shielding layer, causing the shielding layer to be discontinuous and destroying its integrity.
At this time, the shielding layer itself has become the largest source of interference, resulting in its performance being far inferior to that of the unshielded system. When transmitting at high frequencies, shielded wires need to be grounded at both ends, which is more likely to produce a potential difference on the shielding layer. It can be seen that the requirements of the shielding system itself constitute the biggest obstacle to ensuring its performance. A complete shielding system requires shielding everywhere. Once the shielding at any point cannot meet the requirements, it will inevitably affect the overall transmission performance of the system.