TLM — transmission line matrix

TLM (transmission line matrix) is a numerical method that models wave propagation in the cavity using a network of equivalent transmission lines. The Earth-ionosphere cavity is represented by nodes connected by line segments; the propagation and scattering of electromagnetic energy between nodes imitates the actual propagation of a wave through space.

TLM belongs among the time-domain approaches and is conceptually related to FDTD — both discretize space and track the progress of the wave step by step. The network character of TLM offers a natural physical picture: the resonances of the cavity correspond to standing waves in the interconnected network of lines.

TLM complements the palette of modeling methods as an alternative time-domain approach to solving the resonances in the cavity. In the context of SR modeling it is less widespread than TDTE, FDTD and FEM, but it represents a conceptually useful way of viewing the propagation of ELF waves as the transfer of energy through a network of lines.