TABLE OF CONTENTS A general microwave circuit is a multiport (i.e., a circuit with a number of ports) [1 4]. In the network picture, a port is constituted by a pair of external nodes where the currents flowing into the two nodes of a port have equal amplitude and opposite signs. In microwave circuits a multiport usually exhibits waveguide ports. The port is defined by the junction plane of the waveguide. If more than one mode is excited in the junction plane of the waveguide, we have to assign one port to every mode. In the following we assume that in every waveguide only a single transverse waveguide mode is excited. In this case the number of physical ports is identical with the number of ports in the abstract multiport scheme.
Figure 10.1 shows the schematic drawing of a multiport. The port either may be of a coaxial type, a waveguide type, or any other type. To each port a pair of complex amplitudes is assigned; these describe the incident and scattered electromagnetic waves completely. The complex amplitudes are defined for a certain plane of reference in the waveguide termination. To describe the state of the kth port ( k = 1... n) we may take the incident and scattered wave amplitudes a k and b k or the current I k and the voltage V k. Current and voltage may be defined in a conventional way for TEM ports. For...
