10.2 TYPES OF TRANSMISSION LINES

Transmission lines are classified as balanced or unbalanced according to the symmetry of the voltages and currents on their conductors, each suited to particular applications depending on noise immunity, shielding requirements, power handling, and installation constraints. In a balanced line, the voltages on the two conductors are equal in magnitude and opposite in polarity with respect to ground, so that the currents are equal and opposite. In an unbalanced line, one conductor carries the signal while the other is connected to ground (earth) and serves as the return path. Balanced lines are preferred where external noise and interference must be minimized because the symmetry allows unwanted common-mode voltages to cancel at the receiver input.