Complex interaction of passive multiport structures and their description by separate discrete models

It is demonstrated, using the example of a T-junction, that not every multiport structure can be accurately described by a discrete and separated modelling approach at millimetre and sub-millimetre wavelengths. It is shown that especially stub-networks, which are typically used in RF-matching networks, are affected. In this case, the discrete modelling approach predicts a different resonance frequency than the S-parameter measurement as well as the 3D electromagnetic field simulation (3D-EMFS) of the whole structure. However, these resonances are of particular importance for the design of a RF matching network and should be predicted by the model as precisely as possible. Therefore, the reason for the mismatch by accurate 3D-EMFS is investigated and a possible solution on how to model the so-called complex interactions in passive multiport structures at millimetre and sub-millimetre wavelengths is provided.