Industry News

Coaxial loss problem

2021-04-21


Coaxial loss problem

Coaxial cables are widely used in the industry, and their loss has always been a concern. The more high frequency the coaxial line is used, the greater the loss. The specific reasons are as follows.

First, 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 RF line uses Precious metals (high conductivity, precise manufacturing process, etc.).

    Second, the coaxial line 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 line 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).
   Third. The skin depth δ=1/πfuσ; the cross-sectional area of the transmission current s=π[(r+δ)²-r²]; the transmission resistance R=1/σs;
  Finally. The thinner and longer the coaxial cable, the greater the loss, and the higher the signal frequency, the greater the loss.
  The above is the loss of coaxial cable. Coaxial cable is the main product of our company. If you have any questions about coaxial cable, please feel free to contact us. Next, I will share with you some methods to determine the quality of the coaxial line:
1. Observe the roundness of the insulating medium.
2. Detect the consistency of the insulation medium of the coaxial cable.
3. Detect the braided net of the coaxial cable.
4. Check the quality of aluminum foil.
5. Check the tightness of the outer sheath.
6. Observe the shape of the coaxial line into a loop.