About Coaxial Cable Loss

The more high frequency the Coaxial Cable is used, the greater the loss, the reasons are as follows，

 

a. The higher the frequency of the signal, the stronger the skin effect. The more concentrated the transmission on the metal surface, the smaller the transmission cross-sectional area. Therefore, the greater the impedance, the greater the loss. In order to reduce the loss, the radio frequency line uses expensive Metal (high conductivity, precise manufacturing process, etc.).

 

b. Coaxial Cable loss is divided into dielectric loss and metal conductor loss. The main one is dielectric loss. Generally, the relative dielectric constant is low and the dielectric loss angle factor is small, so that the attenuation is small. The medium requires a consistent structure to ensure uniform impedance. The higher the frequency, the more difficult it is to maintain a consistent and continuous impedance, and the reflection loss will be larger.

 

1. Dielectric loss:

When the frequency is high, the dielectric constant is a function of frequency due to the dispersion of the medium. The fundamental reason is that the charged particles change differently with the alternating electric field. The dielectric coefficient changes with frequency should have a maximum value, but because the Coaxial Cable insulation is a highly non-polar material, the dielectric coefficient dispersion from low frequency to high frequency is very weak.

 

2. Conductor loss:

 Strictly speaking, conductor loss can actually be divided into two parts: heat loss and electromagnetic leakage caused by incomplete shielding. The same shielding rate has different shielding effects on electromagnetic waves of different frequencies, and shielding effects on high frequencies. Not as good as low frequency (of course, this is not the main part of the loss).

 

c. Skin depth δ=1/πfuσ; cross-sectional area of transmission current s=π[(r+δ)²-r²]; transmission resistance R=1/σs;

 

  Conclusion: The thicker the wire, the larger the cross-sectional area and the smaller the transmission resistance;

 

The greater the electrical conductivity, the smaller the skin depth and the smaller the cross-sectional area, which increases the transmission resistance; the greater the electrical conductivity, the transmission resistance can be reduced; from the two considerations, the latter is dominant, so the electrical conductivity The greater the rate, the smaller the resistance;

 

The higher the frequency, the smaller the skin depth and the larger the transmission resistance.

 

d. The thinner and longer the Coaxial Cable, the greater the loss, and the higher the signal frequency, the greater the loss.