International Journal of Infrared and Millimeter Waves, VoL 16, No. 3, 1995 ON THE MODAL SPECTRUM OF THE CHANNEL WAVEGUIDE E Frezza and P. Lamparieilo "La Sapienza'" University of Rome, Electronic Engineering Department Via Eudossiana 18, 00184 Roma, Italy Received January 24, 1995 Abstract The modal spectrum of the channel waveguide, that is a rectangular waveguide without one of the side walls, is studied, including higher-order modes. Both cases of the flanged structure and of the open-ended one are considered, solving the characteristic equations in the complex plane. The analysis is of interest for the understanding of recently noticed coupling phenomena in leaky-wave antennas and in shielded planar structures, and for applications to microwave hyperthermia. Key Words: Waveguides; Leaky waves; Antennas. 1. Introduction The so-called channel waveguide [1-5] was introduced for the first time by Rotman many years ago [1]. It is simply a rectangular waveguide where one of the side walls is removed. A ground plane is added for flush mounting (see Fig. 1), or the waveguide may be simply open-ended. The polarization of the electric field is along the y direction, as that of the electric field of the dominant TElo mode in the closed rectangular waveguide, which is used to excite the actual channel waveguide. The modes of this kind are called channel-guide modes. 591 0195-9271/95/0300~0591507.50/0 o 1995 Plenum Publishing Corporation