Do you know the testing method for shielded cables?
There are two methods for measuring shielding attenuation of shielded cables: leakage method and penetration method.
1. Leakage method is to generate a strong electromagnetic field inside a coaxial cable. Due to insufficient shielding of the cable, the strong electromagnetic field between the inner and outer conductors of the cable can leak out through the gaps in the outer conductor. The leakage field strength is measured to characterize the shielding attenuation of the cable, and the absorption clamp method uses the leakage method.
2. Penetration method is to place the tested cable in a uniform electromagnetic field. Due to the gaps in the outer conductor of the cable, the electromagnetic field penetrates into the interior of the cable through the gaps. Measuring the penetration field strength can also characterize the shielding attenuation of the cable. With the development of electromagnetic compatibility measurement equipment, GTEM chambers that can generate uniform transverse electromagnetic fields are used to measure the shielding attenuation of cables. This measurement method is called the GTEM chamber method, which belongs to the permeation method and is more complex than the absorption clamp method. But the GTEM chamber method has a measurement range of DC-1GHz, which is wider than the absorption clamp measurement range. In theory, the electromagnetic field strength that a GTEM chamber can generate is only related to the input signal power, and as long as the power amplifier is large enough, it can generate a high field strength. This greatly improves the sensitivity of measuring shielding attenuation in the GTEM chamber.
