Experimental Demonstration of Degenerate Band Edge in Metallic Periodically Loaded Circular Waveguide

• Published in: IEEE transactions on microwave theory and techniques Vol. 65; no. 11; pp. 4037 - 4045
• Main Authors: Othman, Mohamed A. K., Xuyuan Pan, Atmatzakis, Georgios, Christodoulou, Christos G., Capolino, Filippo
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.11.2017; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Beam interactions; Cavity resonators; Circular waveguides; Coalescing; Compressors; degenerate band edge (DBE); Dispersion; Eigenvectors; Electron beams; Geometry; Group delay; Loaded waveguides; Loss measurement; Microwave sensors; Microwaves; Optical waveguides; Oscillators; Periodic structures; Propagation modes; Q factors; Q-factor; slow-wave structures; Solid state devices; Wave propagation; Wavelengths
• ISSN: 0018-9480; 1557-9670
• DOI: 10.1109/TMTT.2017.2706271

We experimentally demonstrate for the first time the degenerate band edge (DBE) condition, namely, the degeneracy of four Bloch modes, in loaded circular metallic waveguides. The four modes forming the DBE represent a degeneracy of the fourth order occurring in a periodic structure where four Bloch modes, two propagating and two evanescent, coalesce. The DBE is associated with four Bloch eigenmodes representing wave propagation in the periodic structure that coalesce in both wavenumbers and eigenvectors (i.e., polarizations), at a single frequency. It leads to a very flat wavenumber-frequency dispersion relation, and the finite-length structure's quality factor scales as N 5 , where N is the number of unit cells. The proposed waveguide in which DBE is observed here is designed by periodically loading a circular waveguide with misaligned elliptical metallic rings. We validate the existence of the DBE in such structure using measurements, and we report good agreement between full-wave simulation and the measured response of the waveguide near the DBE frequency; taking into account metallic losses. We correlate our finding to theoretical and simulation results utilizing various techniques, including dispersion synthesis, and scaling of the quality factor and group delay with length. Moreover, the reported geometry is only an example of metallic waveguide with DBE: DBE and its characteristics can also be designed in many other kinds of waveguides and various applications can be contemplated as high-power microwave generation in amplifiers and oscillators based on an electron beam interaction or solid-state devices, pulse compressors, and microwave sensors.