Exceptional Points of Degeneracy in Periodic Coupled Waveguides and the Interplay of Gain and Radiation Loss: Theoretical and Experimental Demonstration

We present a novel paradigm for dispersion engineering in coupled transmission lines (CTLs) based on exceptional points of degeneracy (EPDs). We also develop a theory for fourth-order EPDs consisting of four Floquet-Bloch eigenmodes coalescing into one degenerate eigenmode; present unique wave propa...

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Bibliographic Details
Published in:IEEE transactions on antennas and propagation 2019-11, Vol.67 (11), p.6909-6923
Main Authors: Abdelshafy, Ahmed F., Othman, Mohamed A. K., Oshmarin, Dmitry, Almutawa, Ahmad T., Capolino, Filippo
Format: Article
Language:English
Subjects:
Coalescing
Degeneracies
Dispersion
electromagnetic bandgap
Figure of merit
Microstrip
Microwave frequencies
multi-transmission lines (TLs)
Optical waveguides
Oscillators
Periodic structures
Power combiners
Power efficiency
Symmetric matrices
Tolerances
Transmission line matrix methods
Transmission lines
Wave propagation
Waveguides
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Summary:We present a novel paradigm for dispersion engineering in coupled transmission lines (CTLs) based on exceptional points of degeneracy (EPDs). We also develop a theory for fourth-order EPDs consisting of four Floquet-Bloch eigenmodes coalescing into one degenerate eigenmode; present unique wave propagation properties associated with the EPD; develop a figure of merit (FOM) to assess the practical occurrence of the fourth-order EPDs in CTLs with tolerances and losses; and experimentally verify for the first time the existence of a fourth EPD (the degenerate band edge), through dispersion and transmission measurements in microstrip-based CTLs at microwave frequencies. In addition, we report that based on experimental observation and the developed FOM, the EPD features are still observable in structures that radiate (leak energy away), even in the presence of fabrication tolerances and dissipative losses. We investigate the "gain and loss balance" regime in CTLs as a means of recovering an EPD in the presence of radiation and/or dissipative losses, without necessarily resorting to parity-time (PT)-symmetry regimes. The versatile EPD concept is promising in applications such as high-intensity and power-efficiency oscillators, spatial power combiners, or low-threshold oscillators and opens new frontiers for boosting the performance of large coherent sources.
ISSN:0018-926X
1558-2221
DOI:10.1109/TAP.2019.2922778