Transmission Line Theory establishes the mathematical framework describing voltage and current wave propagation along conductors where distributed inductance, capacitance, resistance, and conductance parameters cannot be neglected. This theory relies on the telegrapher's equations to define characteristic impedance, reflection coefficients, standing wave ratios, and phase velocity within a lossless or low-loss domain. It constitutes the fundamental subfield of electromagnetic field analysis required when circuit approximations fail due to electrical dimensions approaching significant fractions of the signal wavelength.
Prerequisite chain context: requires Wave Propagation Constants in Transmission Lines.