Transmission lines

Definition

Transmission lines are specialized cables or other structures designed to conduct alternating current (AC) and radio frequency (RF) signals from one point to another with minimal loss. They are essential in the efficient transfer of electrical energy over long distances.

5 Must Know Facts For Your Next Test

1. Transmission lines have characteristic impedance, typically denoted as $Z_0$, which must match the load impedance for maximum power transfer.
2. The primary parameters of transmission lines include resistance (R), inductance (L), capacitance (C), and conductance (G).
3. Standing wave ratio (SWR) is used to measure the efficiency of power transmission; an SWR of 1:1 indicates perfect impedance matching.
4. Transmission lines can exhibit phenomena such as reflection and refraction when there is a mismatch between line and load impedances.
5. Skin effect causes the AC current to flow near the surface of conductors at higher frequencies, increasing effective resistance.

Review Questions

• What is characteristic impedance in a transmission line and why is it important?
• How do resistance, inductance, capacitance, and conductance affect the performance of a transmission line?
• Explain what happens when there is an impedance mismatch in a transmission line.

Related terms

Characteristic Impedance:

$Z_0$ is the inherent impedance of a transmission line determined by its inductance and capacitance per unit length.

Standing Wave Ratio (SWR): A measure of how efficiently RF power is transmitted from a source through a transmission line into a load.

Skin Effect:

The tendency for AC current to distribute within a conductor such that the current density is largest near the surface, reducing effective cross-sectional area at higher frequencies.