Distributed Degenerate Band Edge Oscillator

Abdelshafy, Ahmed F.; Oshmarin, Dmitry; Othman, Mohamed A. K.; Green, Michael M.; Capolino, Filippo

doi:10.1109/tap.2020.3018539

Cited by 15 publications

(8 citation statements)

References 26 publications

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“…This is similar to the method proposed by Oparina et al where a high-Q supermode is formed inside an oversized cavity based on the Talbot effect [25]. The results presented in this paper have relevance to the research carried out at the University of California, Irvine (UCI) [26][27][28][29][30] where multimode synchronization, provided by four degenerate modes, enables mode selection in similar oversized, 2D structures [28]. The principle of mode selection has previously been demonstrated in 2D-PSLs with planar geometry [31][32][33][34].To obtain high output power at a specified frequency, the dimensions and parameters of the 2D-PSL and the assembled…”

Section: Introductionsupporting

confidence: 83%

“…2(c) indicates a 'split band edge' and demonstrates that the structure can potentially support a degenerate band edge (DBE) [28] where four degenerate modes are implicated in the volume and surface wave coupling. Although this DBE phenomenon is strictly observed in the absence of gain media, the operating regime is only slightly shifted when an electron beam is passed through the structure and therefore certain properties [27], most notably the enhanced mode selectivity facilitated by the mode degeneracy, (and in this case enabled by the coupling of volume and surface waves) are retained [26][27][28][29][30]. While the coupled eigenmode inside the 2D-PSL is similar to a DBE mode, the DBE concept was not used in the design of the oscillator.…”

Section: Dispersion Diagramsmentioning

confidence: 98%

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Efficient, 0.35-THz Overmoded Oscillator Based on a Two-Dimensional Periodic Surface Lattice

MacLachlan

Robertson

Cross

et al. 2022

IEEE Trans. Electron Devices

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We present the theory, design and numerical modeling of a cylindrical, two-dimensional (2D) periodic surface lattice (PSL) intended for use as the interaction region of an electron beam driven, pulsed source. The production of 1.95MW peak, pulsed 0.35THz radiation with an electronic efficiency of 24% is reported. Mode selection in the oversized cavity, where the diameter D is almost 3.5 times larger than the operating wavelength 𝝀, is achieved by coupling volume and surface fields to form a coupled cavity eigenmode.We demonstrate the advantages (including enhanced output power and improved spectral purity) of using a 2D-PSL over a simpler 1D structure. The cylindrical 𝑫 𝝀~𝟑. 𝟓 ⁄ 2D-PSL demonstrates the 'proof-of principle' high-order mode coupling with the potential to increase 𝑫 𝝀 ⁄ to values of 20 or more for the realization of CW 2D-PSL sources or very powerful pulsed sources. The theory is applicable over a broad frequency range.

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Section: Introductionsupporting

confidence: 83%

Section: Dispersion Diagramsmentioning

confidence: 98%

Efficient, 0.35-THz Overmoded Oscillator Based on a Two-Dimensional Periodic Surface Lattice

MacLachlan

Robertson

Cross

et al. 2022

IEEE Trans. Electron Devices

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“…These results motivate the synthesis of DBE in periodic substrate-integrated waveguide (SIW) structures, which have the advantage of being low-cost, compact, are suitable for integration at millimeter-wave frequencies, and suppress radiation losses [30]. DBEs in SIW are therefore attractive for the design of integrated resonators with very high quality factors, and can pave the way to the realization of robust oscillators at high frequencies [29]. Furthermore, opening slots on the upper SIW plate would allow for the design of ultra-sensitive sensors based on the directive radiation of the periodic resonant guided wave.…”

Section: Introductionmentioning

confidence: 99%

“…The rapid growth of Q factors in DBE structures is particularly attractive for the design of high Q-factor resonators in compact size. Of course the presence of losses eventually prevents the fast increase of Q-factor for long DBE resonators; however, this factor can be compensated by introducing distributed elements providing gain to each cell [29]. These results motivate the synthesis of DBE in periodic substrate-integrated waveguide (SIW) structures, which have the advantage of being low-cost, compact, are suitable for integration at millimeter-wave frequencies, and suppress radiation losses [30].…”

Section: Introductionmentioning

confidence: 99%

Synthesis and Measurement of DBE Exceptional Points in Substrate-Integrated Waveguides

Zheng

Casaletti

Abdelshafy

et al. 2022

IEEE Trans. Microwave Theory Techn.

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This paper proposes a method to engineer degenerate band-edge conditions in periodic substrate-integrated waveguides (SIWs). A degenerate band edge is a fourth-order exceptional point originating from the coupling of four Floquet-Bloch modes; it leads to a dispersion relation flatter than a regular band edge and is suitable to design slow-wave structures and high Q-factor resonators. Design guidelines to achieve a degenerate band edge point are given based on Bloch analyses of unit cells. An oblique line of vias in SIW is proposed to form a suitable modal coupling between adjacent waveguides enabling a degenerate band-edge condition. The effect of losses and the robustness to parameter variations are discussed by means of rigorous Bloch analyses. A unit cell showing the best behavior concerning the losses and geometric tolerances is selected and prototypes of finite-length resonators are realized. Measurements validate simulated results and confirm the typical N 5 scaling of the loaded Q factor to the number of cells N of the resonator.

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“…We employ the Puiseux fractional power expansion series to illustrate the bifurcation of the system's dispersion diagram at the EPD [17]. The EPD has been studied for its applications in sensing devices [18], [19] and oscillators [20], [21], [22], [23].…”

mentioning

confidence: 99%

Exceptional Degeneracies in Traveling Wave Tubes with Dispersive Slow-Wave Structure Including Space-Charge Effect

Rouhi,

Marosi,

Mealy

et al. 2021

Preprint

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The interaction between a linear electron beam and a guided electromagnetic wave is studied in the contest of exceptional points of degeneracy (EPD) supported by such an interactive system. The study focuses on the case of a linear beam traveling wave tube (TWT) with a realistic helix waveguide slow-wave structure (SWS). The interaction is formulated by an analytical model that is a generalization of the Pierce model, assuming a one-dimensional electron flow along a dispersive single-mode guiding SWS and taking into account space-charge effects in the system. The augmented model using phase velocity and characteristic impedance obtained via full-wave simulations is validated by calculating gain versus frequency and comparing it with that from more complex electron beam simulators. This comparison also shows the accuracy of our new model compared with respect to the non-dispersive Pierce model. EPDs are then investigated using the augmented model, observing the coalescence of complex-valued wavenumbers and the system's eigenvectors. The point in the complex dispersion diagram at which the TWT-system starts/ceases to exhibit a convection instability, i.e., a mode starts/ceases to grow exponentially along the TWT, is the EPD. We also demonstrate the EPD existence by showing that the Puiseux fractional power series expansion well approximates the bifurcation of the dispersion diagram at the EPD. This latter concept also explains the "exceptional" sensitivity of the TWT-system to changes in the beam's electron velocity when operating near an EPD.

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Distributed Degenerate Band Edge Oscillator

Cited by 15 publications

References 26 publications

Efficient, 0.35-THz Overmoded Oscillator Based on a Two-Dimensional Periodic Surface Lattice

Efficient, 0.35-THz Overmoded Oscillator Based on a Two-Dimensional Periodic Surface Lattice

Synthesis and Measurement of DBE Exceptional Points in Substrate-Integrated Waveguides

Exceptional Degeneracies in Traveling Wave Tubes with Dispersive Slow-Wave Structure Including Space-Charge Effect

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