How does transmission line theory apply to high-frequency circuit analysis?

At high frequencies where wavelength is comparable to conductor length, lumped circuit analysis fails. Transmission lines have distributed L, C, R, G parameters per unit length. Key concepts include characteristic impedance Z0 = sqrt((R+jwL)/(G+jwC)), propagation constant gamma, and reflection coefficient. Standing waves occur with impedance mismatch, measured by VSWR. Smith charts visualize impedance matching. Applications include RF/microwave circuits, high-speed digital interconnects, and PCB trace design.