Symmetrical reactive bipolar networks, which include microwave filters, constitute
the most commonly used class of passive electrical circuits in practice. This chapter develops
analytical models of these circuits in relation to their implementation on the basis of multi-wire
systems of coupled microstrip lines. Such systems are characterized by the inequality of the
residue mode phase velocities, which is due to the inhomogeneity of the substrate-air medium.
The substitution networks for this type of symmetric network are defined as an equivalent mode
representation, which forms the basis for the analysis and synthesis of high-selective filters.
The operating principle of these filters is built upon the inequality effect of residue modes phase
velocities. The relationship between the amplitude-frequency response and the group delay time
of symmetric networks of both minimum phase and non-minimum phase types has been
revealed.
Keywords: Dielectric substrate, Electromagnetic waves, Frequency response, High-selective filter, Microwave network, Microstrip line, Microwave range, Phase velocity, Symmetrical structures.
