Novel Propagation Model of Degenerate Band Edge Modes Using Dual   Non-identical Pair of Coupled Transmission Lines
  We present a novel propagation medium using a pair of non-identical coupled transmission lines. The medium is referred to as `butterfly' structure and is composed of four coupled transmission lines. These four coupled transmission lines generate higher-order dispersion modes by coupling the modes supported on each of the transmission lines. When these transmission line pairs are placed inside a circular waveguide, they support a strong TM01-like Degenerate Band Edge mode. This property can be used to enhance coupling of the electron beams to RF waves for high-power Traveling Wave Tubes. In this paper, we present the slow wave characteristics and Degenerate Band Edge mode formation using the coupled pair of transmission lines. 
Muhammed Zuboraj, Kubilay Sertel, John L. Volakis
physics.class-ph physics.optics