Q.What is the purpose of using transmission lines in communication?

A transmission line is a system of conductors that carries electrical energy — as guided electrical waves — from one point to another, for example linking a transmitter or receiver to its antenna. Three types are common: the open-wire (two-wire) line, the co-axial cable, and the waveguide.

A transmission line is not a pair of ideal wires; its electrical properties are distributed along its length. Every short section has series resistance R and series inductance L (from the wires), a shunt capacitance C between the conductors, and a shunt conductance G (from leakage through the imperfect dielectric). The line is therefore modelled as a ladder network of series R-L sections with shunt C-G branches. At radio (high) frequencies $\omega L \gg R$ and $\omega C \gg G$, so R and G may be neglected and the line reduces to a low-loss LC ladder. …