  Typical features of the Transmission Line Matrix (TLM) algorithm in
connection with stub loading techniques and prone to be hidden in common
frequency domain formulations are elucidated within the propagator approach to
TLM. In particular, the latter reflects properly the perturbative character of
the TLM scheme and its relation to gauge field models. Internal 'gauge' degrees
of freedom are made explicit in the frequency domain by introducing the complex
nodal S-matrix as a function of operators that act on external or internal
fields or virtually couple the two. As a main benefit, many techniques and
results gained in the time domain thus generalize straight away. The recently
developed deflection method for algorithm synthesis, which is extended in this
paper, or the non-orthogonal node approximating Maxwell's equations, for
instance, become so at once available in the frequency domain. In view of
applications in computational plasma physics, the TLM model of a relativistic
charged particle current coupled to the Maxwell field is treated as a
prototype.
