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Characteristic Impedance of Transmission Line

The region through which a plane wave (unguided wave) travels is characterised by the intrinsic impedance (η) of the medium defined by the ratio of the electric field to the magnetic field. The guiding structure over which the transmission line wave (guided wave) travels is characterised the characteristic impedance (Z0) of the transmission line defined by the ratio of voltage to current.
Characteristic impedance of a transmission line is defined as the ratio of positively travelling voltage wave to current wave at any point on the line.

Lossless Transmission Line

A transmission line is said to be lossless if
  • the conductors of the line are perfect, i.e., the conductors have infinite conductivity and zero resistance (σ = ∞, R = 0), and
  • the dielectric medium between the conductors is ideal, i.e., the medium has zero conductivity and infinite resistance (σ = 0, G = 0).

Distortionless Transmission Line-Waveform Distortion

When the received signal is not identical with the transmitted signal, the signal is said to be distorted. There are two types of waveform distortion:
  1. Frequency Distortion
    During the transmission of a signal on a transmission line, it gets attenuated through attenuation constant α. It is known that α is a function of frequency.
    Description: 18576.png
    Hence, different frequencies transmitted along the line will then be attenuated to different extents. The received waveform will not be identical with the input waveform. This is known as frequency distortion.
  2. Phase Distortion
    The phase constant is given as,
    Description: 16837.png
    and velocity is given as,
    Description: 18148.png

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