Propagation of Degenerate Band-Edge Modes Using Dual Nonidentical Coupled Transmission Lines
AbstractDegenerate band-edge (DBE) modes are known for their exceptionally high field intensity at the nearly flat dispersion-diagram profile. Because of the latter property, resonances supported by these modes are associated with a very strong field at the band edge. DBE modes and similar resonances of this class have been typically realized by introducing anisotropic dielectric slabs in volumetric photonic crystals. By contrast, in this paper, we present an analytic model of DBE modes using a simple set of nonidentical coupled transmission lines. The unequal phase velocities of the supported waves supported by these transmission lines lead to mode degeneracy, that in turn provide quartic solutions of dispersion (ω-β) relations. The DBE mode appears as one these quartic solutions. As such, the proposed model generalizes the concept of DBE modes using the construct of nonidentical coupled transmission lines. In this paper, we also propose a propagation medium using a dual pair of nonidentical transmission lines. The medium is referred to as a “butterfly” structure and is composed of four coupled transmission lines. These four coupled transmission lines generate the TM01-like degenerate band-edge mode. This is done by coupling the TE modes supported on each pair of the transmission lines. Mode purity at the resonance frequency and the intense field profile on the axis are properties that can be exploited for high-power microwave sources.