To the author’s knowledge

not so much has been discussed about the excitation of cavities by a waveguide. In analyzing this problem

it is necessary to consider the re-excitation of the waveguide by the excited cavity. Here the author utilizes the concept of an equivalent exciting field

which conveniently takes into account both the exciting and the reexciting fields.Equivalent networks of the waveguide-cavity system

as well as their parameters

are obtained. The form of the networks and values of their parameters depend upon how waveguide and cavity are connected

and on the coupling parameter and tuning of the cavity.The above results are verified by the measurement of a cavity wavemeter of the absorption type working on 3-cm wavelength.