The ultimate target of any analysis tool is the simulation of complex systems or subsystems involving filters, amplifiers, couplers and so on. In the previous chapter we have treated structures by assuming they were uniform along the propagation direction, namely, we dealt with 2D structures. The greater part of the information obtained may be directly used in the complete 3D design: once the characteristic impedance and the propagation constant of a transmission line are known, it is possible, to a first degree of approximation, to treat by a circuit approach a system involving cascaded lines or interconnected subsystems. Each element is treated by means of its matrix representation (whatever matrix has been selected: S, Z, transmission matrix...) and the matrix representation of the complete system may be computed by composing the matrix representation of each subpart. However, this way we are neglecting what happens when different structures are interconnected together, that is, whenever there is an abrupt change in a structure along the propagation direction of the wave. In this case, we have what is named a “discontinuity”, that is, a genuine 3D problem.

Inspec keywords: transmission lines; substrate integrated waveguides; planar waveguides; matrix algebra

Other keywords: interconnected subsystem; matrix representation; passive planar waveguide; multilayered substrate; active planar waveguide; cascaded line; transmission line; circuit approach

Subjects: Waveguides and microwave transmission lines