A field theoretical derivation of the three-dimensional TLM method wit
h expanded node and of the three dimensional TLM method with asymmetri
cal condensed node is given, In the derivation, the Method of Moments
is applied to Maxwell's equations, The wave amplitudes are related to
the tangential field components at the boundaries of the TLM cell, The
same approach is applied to derive the FDTD method from Maxwell's equ
ations. A complete dispersion analysis is given for the two TLM method
s as well as for the FDTD method.