Experimental Validation of Frozen Modes Guided on Printed Coupled Transmission Lines

Apaydin, Nil; Zhang, Lanlin; Sertel, Kubilay; Volakis, John L.

doi:10.1109/tmtt.2012.2192746

Cited by 42 publications

(28 citation statements)

References 28 publications

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“…Therefore, the most unique DBE characteristic of a periodic waveguide is its respective dispersion diagram which portrays how the phase changes with frequency over the passband of the structure. Although different approaches exist to estimate the dispersion diagram of a waveguide from a measurement on the finite length waveguide (see [11] for example), we use a synthetic method [35] based on the measurement of the resonance frequencies of the cavity formed in Fig. 1.…”

Section: B Reflection Measurementsmentioning

confidence: 99%

“…The band edge condition is normally associated with slow-wave properties in the sense that group velocity exhibits substantial reduction near the band edge [7]- [10]. Resonators made of waveguides that support modes with extremely low group velocity possess very high quality (Q) factor [3], [9], [11]- [13] and therefore are very suitable to applications including filters, pulse forming networks, in high power microwave generation [14] and in RF accelerators [15].…”

Section: Introductionmentioning

confidence: 99%

“…Indeed, the DBE has been shown to provide unprecedented enhancement in the Q factor and field enhancement over RBE structures as demonstrated theoretically in [10], [19]. Furthermore, applications featuring slow-light properties associated with the DBE has been proposed such as small/directive antennas [12], [20]- [23], lowthreshold switching [10], [13], pulse compression [24], and filters [11]. The theory of four mode degeneracy was furthermore utilized for the first time to show giant gain enhancement [10] in slow-wave structures with DBE, for high power amplifiers [17] and oscillators [18], [25], when interacting with an electron beam.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

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

Othman¹,

Pan

Atmatzakis

et al. 2017

IEEE Trans. Microwave Theory Techn.

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Abstract-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 fourth order occurring in a periodic structure where four Bloch modes, two propagating and two evanescent, coalesce. It leads to a very flat wavenumber-frequency dispersion relation, and the finitelength 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, supported by a low-index dielectric. 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, as well as observing how quality factor and group delay scale as the structure length increases. 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 microwave generation in amplifiers and oscillators based on an electron beam interaction or solid state devices, pulse compressors and microwave sensors.Index Terms-Degenerate band edge (DBE), slow-wave structures, cavity resonators.

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Section: B Reflection Measurementsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

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

Othman¹,

Pan

Atmatzakis

et al. 2017

IEEE Trans. Microwave Theory Techn.

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“…Therefore, at an EPD one expects that the conjugate-symmetry condition (19) is no longer rigorously satisfied due to the extra radiation (scattering) losses in the chain. Nevertheless, as we show below, an EPD can still occur since a gain/loss balance can be achieved from the condition in (18). On the other hand, if one chooses the perfect conjugate symmetry condition (19) on the chain, an ideal EPD (where the eigenvectors are rigorously degenerate) can no longer be identified.…”

Section: Ii) Effect Of Gf Phase Retardationmentioning

confidence: 97%

“…5, we show the mode evolution in the complex k zplane [Re(k z )−Im(k z ) plane] as the frequency increases. As it can be observed, the modal wavenumbers are almost real, i.e., We also investigate the detuning of the second-order EPD by varying the gain and loss values implemented in the polarizabilities from their optimal condition (18). For that purpose, we assume an exact gain and loss symmetry in the chain, i.e., ).…”

Section: Ii) Effect Of Gf Phase Retardationmentioning

confidence: 99%

Exceptional points of degeneracy andPTsymmetry in photonic coupled chains of scatterers

2017

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We demonstrate the existence of exceptional points of degeneracy (EPDs) of periodic eigenstates in nonHermitian coupled chains of dipolar scatterers. Guided modes supported by these structures can exhibit an EPD in their dispersion diagram at which two or more Bloch eigenstates coalesce, in both their eigenvectors and eigenvalues. We show the emergence of a second-order modal EPD associated with the parity-time (PT) symmetry condition, at which each particle pair in the double chain exhibits balanced gain and loss. Furthermore, we also demonstrate a fourth-order EPD occurring at the band edge. Such degeneracy condition was previously referred to as a degenerate band edge in lossless anisotropic photonic crystals. Here, we rigorously show it under the occurrence of gain and loss balance for a discrete guiding system. We identify a more general regime of gain and loss balance showing that PT-symmetry is not necessary to attain EPDs. Moreover, we investigate the degree of detuning of the EPD when the geometrical symmetry or balanced condition is broken. Furthermore, we demonstrate a realistic implementation of the EPD in a coupled chain made of pairs of plasmonic nanospheres and active core-shell nanospheres at optical frequencies. These findings open unprecedented avenues toward superior light localization and transport with application to high-Q resonators utilized in sensors, filters, low-threshold switching and lasing.

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Dispersion Engineering for Slow‐Wave Structure Design

Chipengo

Nahar

Volakis

et al. 2021

High Power Microwave Sources and Technologies Using Metamaterials

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Experimental Validation of Frozen Modes Guided on Printed Coupled Transmission Lines

Cited by 42 publications

References 28 publications

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

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

Exceptional points of degeneracy andPTsymmetry in photonic coupled chains of scatterers

Dispersion Engineering for Slow‐Wave Structure Design

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