Q.Draw the equivalent circuit of Transmission line. Explain the primary and secondary constants.

A transmission line is represented by a ladder equivalent circuit with series resistance R and inductance L and shunt capacitance C and conductance G distributed along its length. R, L, C and G are its four primary constants; the attenuation, phase-shift and propagation constants are its secondary constants. …

[!TLDR]

The line is a ladder of series R and L with shunt C and G (its four primary constants); its secondary constants are the attenuation constant $\alpha$, phase-shift constant $\beta$ and propagation constant $\gamma=\alpha+j\beta$.

Equivalent circuit: A transmission line can be represented by a repeated ladder network. Each small section has a series resistance R and a series inductance L along the conductor, together with a shunt capacitance C and a shunt conductance G between the two conductors. At high (radio) frequencies the inductive reactance is much greater than R and the capacitive susceptance is much greater than G, so R and G are neglected and the line reduces to a simple LC ladder.

Primary constants (four): these describe the line per unit length.

1. Series resistance R - due to the resistance of the conductors; R per unit length is proportional to the square root of frequency.
2. Series inductance L - due to the magnetic field around the current-carrying conductors; for a two-wire line $L=\dfrac{\mu}{2}\log\!\left(\dfrac{2D}{d}\right)$, where $D$ is the spacing between the wires and $d$ the wire diameter.
3. Shunt capacitance C - because the two conductors, separated by a dielectric, act as a capacitor; $C\cong\dfrac{\mu\varepsilon}{\log(2D/d)}$.
4. Shunt conductance G - due to the leakage of current through the imperfect dielectric between the conductors (dielectric loss).

Secondary constants: these describe how a wave behaves as it travels along the line and are derived from the primary constants.

1. Attenuation constant $\alpha$ - gives the rate at which the amplitude of the wave decreases (attenuates) as it moves along the line (measured in neper or dB per unit length).
2. Phase-shift constant $\beta$ - gives the phase change of the wave per unit length of the line (radian per unit length). …