2020/03/09 by Tarek Mealy, Filippo Capolino · 1 citation
Engineering · Materials Science · Physics and Astronomy · #Advanced Antenna and Metasurface Technologies #Degeneracy (biology) #Degenerate energy levels #Electric power transmission #Invariant (physics) #Lossless compression #Lossy compression #Metamaterials and Metasurfaces Applications #Microstrip #Microwave Engineering and Waveguides #Planar #Series (stratigraphy) #physics.app-ph
paper · pdf · doi:10.1109/tmtt.2020.2999498
arxiv created 2020/03/09 · openalex publication_date 2020/06/15 · openalex created_date 2020/06/19 · arxiv updated 2020/08/26 · openalex updated_date 2026/08/06
We present the general conditions to realize a fourth-order exceptional point of degeneracy (EPD) in two uniform (i.e., invariant along z) lossless and gainless coupled transmission lines (CTLs), namely, a degenerate band edge (DBE). Until now the DBE has been shown only in periodic structures. In contrast, the CTLs considered here are uniform and subdivided into four cases where the two TLs support combinations of forward propagation, backward propagation, and evanescent modes (when neglecting the mutual coupling). We demonstrate, for the first time, that a DBE is supported in uniform CTLs when there is proper coupling between: 1) propagating modes and evanescent modes, 2) forward and backward propagating modes, or 3) four evanescent modes (two in each direction). We also show that the loaded quality factor of uniform CTLs exhibiting a fourth-order EPD at k = 0 is robust to series losses due to the fact that the degenerate modes do not advance in phase. We also provide a microstrip possible implementation of a uniform CTL exhibiting a DBE using periodic series capacitors with very subwavelength unit-cell length. Finally, we show an experimental verification of the existence DBE for a microstrip implementation of a CTL supporting coupled propagating and evanescent modes.