Typical features of the Transmission Line Matrix (TLM) algorithm inconnection with stub loading techniques and prone to be hidden in commonfrequency domain formulations are elucidated within the propagator approach toTLM. In particular, the latter reflects properly the perturbative character ofthe TLM scheme and its relation to gauge field models. Internal 'gauge' degreesof freedom are made explicit in the frequency domain by introducing the complexnodal S-matrix as a function of operators that act on external or internalfields or virtually couple the two. As a main benefit, many techniques andresults gained in the time domain thus generalize straight away. The recentlydeveloped deflection method for algorithm synthesis, which is extended in thispaper, or the non-orthogonal node approximating Maxwell's equations, forinstance, become so at once available in the frequency domain. In view ofapplications in computational plasma physics, the TLM model of a relativisticcharged particle current coupled to the Maxwell field is treated as aprototype.