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Factors Affecting The Attenuation Constant
Feb 02, 2018

Attenuation of RF cable is related with conductors, media, structure size, process level and the frequency of work.


1: Below 50MHz the attenuation constant is too large or too high, and there is marging on high frequency, often caused by the conductor conductivity is too low or aluminum-plastic composite tape in the aluminum-based is too thin. At low frequency, the aluminum-based the thickness is less than or equal to the transmission depth of the frequency, resulting in αR is too large. According to theoretical calculations, the transmission depth of the aluminum layer at f = 50 MHz is 12.2 μm. Generally take 12 ~ 15μm aluminum can solve this problem. (Of course, if you consider the requirements of shielding attenuation can be properly thickened)


2: Select the PE in the frequency of use of tanδ larger, such as to reach x × 10-3 level, it will result in insulation tanδ increases, so that the attenuation of the cable increases. Therefore, we should pay attention to two issues, first is tanδ should be small (such as the tanδ at 400MHz is 2 ~ 4 × 10-4, the smaller the better), second is process performance (such as the melt index of 0.5 to 10) should be suitable for insulation. The extrusion, different melt index have different temperatures.


3: The outer conductor braiding generally 60% -80% is appropriate, too large to reduce the attenuation effect is not very obvious.


4: Mold design and processing for insulation production are also the key points, and products should be guaranteed to have an even and uniform structure so that the equivalent dielectric constant reaches the design requirements.


5: Physical foam PE attenuation is qualified at low frequencies, and high frequency (such as over 800MHz) is ultra-poor, mostly is related with the dielectric loss tangent and the equivalent dielectric constant is too large, or with the outer conductor density is small, small diameter of the inner conductor. In addition, the attenuation constant also depends on the degree of foaming. Appropriately increasing the degree of foaming within the allowable range of impedance and echoes, which can be achieved by increasing the foaming degree, increasing the impedance and decreasing the attenuation, can help increase the attenuation constant of the cable and at the same time reduce the cost.


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