Pair Of Degenerate Modes Research Articles

A low-profile wideband circularly polarized metasurface antenna based on characteristic mode analysis

Abstract A low-profile wideband circularly polarized (CP) metasurface antenna is demonstrated for C-band applications. The metasurface consists of 4 × 4 square patches with Z-shaped slots. Characteristic mode analysis is used to investigate the modal behavior of the metasurface, and a pair of degenerate modes is chosen as the operating modes. The CP radiation is realized by exciting a pair of degenerate modes of the metasurface through a slot antenna, which is used as a feed structure with a 90° phase difference. The CP bandwidth is further widened by combining the resonance modes of the metasurface and slot antenna. The measured results show that the −10 dB impedance bandwidth of the antenna is 3.47–4.76 GHz, and the 3 dB axial ratio bandwidth is 3.5–4.9 GHz with a peak gain of 6.9 dBic. Moreover, the antenna exhibits well left-hand CP radiation performances with a low profile of 0.046λ0.

Modal dynamics of self-excited thermoacoustic instabilities in even and odd numbered networks of lean-premixed combustors

Can-to-can acoustic interactions in a circumferential network of lean-premixed combustors have a prominent role in the development of complicated modal dynamics and large-scale pattern formations in can-annular gas turbine combustion systems. Despite recent progress in understanding these instabilities, however, previous relevant studies have been limited to an even number of constituent combustors; a fundamental characteristic of the modal dynamics in a can-annular arrangement consisting of an odd number of combustors remains unknown. To address this question, we compare key features of thermoacoustic instabilities in four-coupled (N = 4) and five-coupled (N = 5) can-annular combustor configurations obtained over a broad range of operating conditions. In conjunction with FEM-based Helmholtz simulations, our experimental data show that the dynamic behavior of the even-N case is characterized by the well-known interaction pattern, out-of-phase alternating modulations among the networked combustors. For the odd-N case, however, the can-annular system features complex phase dynamics originating from simultaneous excitation of the degenerate mode pair. We highlight that the development of self-excited azimuthal instabilities in the annular cross-talk section is associated with the modal interaction of the degenerate pair in the odd-N configuration. The initially degenerate pair can be split into two closely-spaced non-degenerate modes, and in consequence their modal interaction gives rise to a periodic transition between spinning and standing azimuthal modes in the annulus. Despite the formation of remarkably different inter-combustor interactions in the two can-annular configurations, however, the entire set of instability data collapses into very similar frequency regimes, suggesting the importance of flame-acoustic interactions occurring within each combustor, namely intra-combustor interactions.

Dual-Band Substrate Integrated Waveguide Filters Based on Multi-Mode Resonator Overlapping Mode Control

In this paper, a multi-mode resonator (MMR) overlapping mode control technique is proposed to realize dual-band substrate-integrated waveguide (SIW) bandpass filters (BPFs). A pair of via perturbations and two kinds of slotlines are introduced to control the overlapping modes. Five resonant modes TM110 (a pair of degenerate modes), TM210 (a pair of degenerate modes) and TM020 are perturbed to realize the dual-band filters. The degenerate modes can be rearrange by the via perturbations, and the overlapping modes can be adjusted by the slotlines. Thus, two kinds of dual-band filters can be realized in a single resonant cavity. Then a two-cavity dual-band filter is proposed to realize better out-band suppression and return loss performance. The proposed two-cavity dual-band BPF is synthesized, designed, fabricated, and measured, realizing the 3-dB fractional bandwidth (FBW) of 6.1% and 7.7% at Q-band and V-band, respectively.

Design of a highly mode-selective photonic lantern for IM/DD MDM transmission

Recently mode multiplexers and demultiplexers (MMUX/MDEMUX) based on photonic lantern (PL) techniques for few-mode fiber transmission have attracted great interest. However, the design of PLs with high modal selectivity has become a great challenge for weakly-coupled mode-division-multiplexing (MDM) applications. In this paper, we propose a highly mode-selective PL-MMUX/MDEMUX design for intensity-modulation/direct-detection MDM transmission adopting each non-degenerate mode or each pair of degenerate modes as an independent channel. For the PL-MMUX, differential-phase injection (DPI) scheme is adopted for each pair of degenerate modes and a corresponding low-modal-crosstalk dissimilar core arrangement method is proposed considering the interleaving positive and negative phase characteristics of modal lobes of degenerate linearly-polarized (LP) modes, which achieve very high modal selectivity. For the PL-MDEMUX, simultaneous reception of degenerate modes is achieved by combining the optical power of both degenerated modes utilizing non-mode-selective PLs. Numerical simulations for a 6-LP-mode PL-MMUX/MDEMUX are performed. Results show that the PL-MMUX with DPI scheme and proposed cores distribution achieve much lower modal crosstalk than other cores distributions and the overall modal crosstalk of the PL-MMUX and MDEMUX in back-to-back case is lower than -20.63 dB over the C-band for all modes. The tolerance of our design to imperfect fabrication of differentiator or environmental impact are also discussed. The proposed DPI and dissimilar core arrangement method have high expansibility and provide a new way for the design of highly selective PLs and are beneficial to the practical applications of weakly-coupled MDM transmission systems and networks.

In-Band Full-Duplex Filtering Antenna Arrays Using High-Order Mode Cavity Resonators

In this article, a series of narrowband and wideband in-band full-duplex (IBFD) filtering antenna arrays (FAAs) using cavity-based high-order modes are investigated. It is found that the pairs of degenerate high-order modes in a single cavity resonator, TM <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{1n0}$ </tex-math></inline-formula> and TM <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{n10}$ </tex-math></inline-formula> ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$n$ </tex-math></inline-formula> is even), are suitable for the IBFD FAA designs due to their advantages: 1) in-phase and same amplitude for each magnetic loop, which helps to enhance the gain, and 2) the modal orthogonality, which guarantees the isolation and cross-polarization level between two channels. The higher order response can be achieved by cascading more high-order mode resonators with the required external quality factor ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q_{e}$ </tex-math></inline-formula> ) and coupling coefficient ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$K$ </tex-math></inline-formula> ). For proof of concept, two types of full-duplex waveguide arrays are implemented and tested. First, a second-order IBFD FAA with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$6\times $ </tex-math></inline-formula> 5 elements, using a pair of degenerate modes TM610 and TM160, is designed with 1% overlapped 10-dB bandwidth and 18.4-dBi realized gain within the passband. The method to improve realized gain and isolation level without increasing any circuit volume is also presented. Second, a fifth-order IBFD FAA using TM410 and TM140 modes is implemented with an overlapped 10-dB bandwidth of 15.6% and a realized gain of 12.5 dBi. The measured isolation between the two channels is better than 40.4 dB. An excellent agreement between simulated and measured results verifies that the proposed design methodology is feasible for designing high-order mode IBFD FAA.

Coherent Control of Topological States in an Integrated Waveguide Lattice.

Topological photonics holds the promise for enhanced robustness of light localization and propagation enabled by the global symmetries of the system. While traditional designs of topological structures rely on lattice symmetries, there is an alternative strategy based on accidentally degenerate modes of the individual meta-atoms. Using this concept, we experimentally realize topological edge state in an array of silicon nanostructured waveguides, each hosting a pair of degenerate modes at telecom wavelengths. Exploiting the hybrid nature of the topological mode, we implement its coherent control by adjusting the phase between the degenerate modes and demonstrating selective excitation of bulk or edge states. The resulting field distribution is imaged via third harmonic generation showing the localization of topological modes as a function of the relative phase of the excitations. Our results highlight the impact of engineered accidental degeneracies on the formation of topological phases, extending the opportunities stemming from topological nanophotonic systems.

Bandwidth-Enhanced Circularly Polarized Slot Antenna and Array Under Two Pairs of Degenerate Modes in a Single Resonant Cavity

A novel design concept of bandwidth-enhanced full-metal circularly polarized (CP) cavity-backed slot antenna and array based on two pairs of degenerate modes in a single cavity is proposed in this paper. Conventional CP antenna based on one pair of degenerate modes only has one axial-ratio (AR) minima and causes a narrow AR bandwidth. Two pairs of degenerate modes in a proposed multimode cavity resonator can initially produce two separate CP operating bands. Then, a pair of metal prisms is introduced to allocate the two bands in proximity to each other, thus obtaining a wide operating bandwidth with two AR minima. As the radiation slots are directly fed by the electric field of the cavity modes, 2 × 2 cross slots are placed on the top wall so as to comprise a CP array. As such, a very simple wideband CP antenna array is realized by virtue of a single multiple-mode resonator without needing extra power dividers. Finally, the 2 × 2 wideband CP antenna array is fabricated and measured. Measurement shows that the proposed antenna array can achieve 15% bandwidth, a peak gain of 11.8 dBic, and a peak total efficiency of 96%.

A Novel Design and Development of a Strip-Fed Circularly Polarized Rectangular Dielectric Resonator Antenna for 5G NR Sub-6 GHz Band Applications.

In this article, a rectangular dielectric resonator antenna (RDRA) with circularly polarized (CP) response is presented for 5G NR (New Radio) Sub-6 GHz band applications. A uniquely shaped conformal metal feeding strip is proposed to excite the RDRA in higher-order mode for high gain utilization. By using the proposed feeding mechanism, the degenerate mode pair of the first higher-order, i.e., at 4.13 GHz and at 4.52 GHz is excited to achieve a circularly polarized response. A circular polarization over a bandwidth of ~10%, in conjunction with a wide impedance matching over a bandwidth of ~17%, were attained by the antenna. The CP antenna proposed offers a useful gain of ~6.2 dBic. The achieved CP bandwidth of the RDRA is good enough to cover the targeted 5G NR bands around 4.4–4.8 GHz, such as n79. The proposed antenna configuration is modelled and optimized using computer simulation technology (CST). A prototype was built to confirm (validate) the performance estimated through simulation. A good agreement was observed between simulated and measured results.

Low-profile linear polarization conversion metasurfaces using degenerate modes for high selectivity

In this paper, two ultrathin polarization conversion metasurfaces (PCMs) were designedfor linear polarization of electromagnetic waves. A method of controlling degenerate modes was applied for enhanced selectivity. The surface resonator is a square patch etched with orthogonal cross-slots. Adjustment of the cross-slot size is beneficial as it introduces a perturbation factor and controls the splitting of the degenerate modes. The constructed dual-mode single-band and four-mode dual-band PCMs with different pairs of degenerate modes can efficiently reflect linear polarized waves to the orthogonal polarization counterpart in the range of 5.89–6.4 GHz and 5.88–6.30 GHz/8.19–8.59 GHz, respectively. Current distribution and an equivalent circuit model were studied to reveal the polarization conversion mechanism. Finally, experiments were implemented to verify the near unity cross-polarization conversion efficiency at the corresponding bands. Given the PCM’s advanced performance of low profile and high selectivity, it has great potential applications in controlling the polarization state of microwaves.

Compact dual-band balanced bandpass filter based on circular SIW cavity

Abstract A compact dual-band balanced bandpass filter with high frequency selectivity and adjustable passband based on the perturbed circular substrate integrated waveguide cavity is firstly proposed in this paper. Two pairs of metallic vias are located at 45°direction of cavities to separate a pair of degenerate modes (TM110 modes) to achieve the differential-mode (DM) dual-band response. Moreover, the perturbation vias can also be used to control the center frequency of the second DM passband while the first one still stays unaffected. The introduction of source-load coupling makes the filter exhibit excellent selectivity. And four controllable transmission zeros appear near two DM passbands. Finally, good common-mode suppression has been got owing to the proposed balanced structure. The measured results are in accordance with the simulated ones well.

A circularly polarized microstrip patch antenna with enhanced bandwidth based on substrate integrated waveguide techniques

In this article, a circularly polarized (CP) microstrip patch antenna (MPA) is proposed. The antenna adopts a substrate integrated waveguide (SIW) cavity and a microstrip patch as the feed structure and the radiator, respectively. In consequence, the patch dominates the radiation and improves the radiation efficiency, while the asymmetric SIW cavity enhances the bandwidth and generates a pair of degenerate modes, which provide the quadrature phase shift that the CP radiation requires. By this mean, the proposed antenna not only brings up a novel feed structure for CP MPA and improves its effective bandwidth, but also circumvent the limitation of the SIW cavity slot antenna, which is low radiation efficiency. Plus, the presented antenna remains the advantages of SIW structure, including high Q factor, high integrate compatibility, and so forth. The antenna was fabricated and measured, and the presented antenna exhibits an impedance bandwidth of 12% (from 2.09 to 2.36 GHz), an axial ratio bandwidth of 7.73% (from 2.15 to 2.32 GHz) with a minimum gain of 7.89 dB. The experiment results indicate a good agreement with the simulation.

Higher-Order-Mode Triple Band Circularly Polarized Rectangular Dielectric Resonator Antenna

The paper presents a triband circular polarized rectangular dielectric resonator antenna. A single coaxial cable feeds the DRA to a double stub strip on the DRA side. A patch strip coupled to the feed assists in widening the bandwidth of the proposed DRA. The degenerate mode pair TE∂11x and higher-TE∂23x has been excited to achieve CP and enhance the antenna gain. The higher-order mode has been excited using a low-cost simple excitation mechanism without compromising on the size and shape of the DRA. An impedance bandwidth of 48% with a gain ~6–9 dBic was achieved in all resonance frequencies. Additionally, the AR bandwidth of 5.5%, 4.2%, and 2.76% was obtained at three different frequencies. Note that the proposed DRA exhibits a wide beamwidth of 112o, which is good for better signal reception. A comparison between the measured with simulated results shows that the measured results are matched by the simulated result trends.

A single‐feed circularly polarized loop antenna using characteristic mode analysis

A novel method for a single-feed circularly polarized (CP) loop antenna with both broad impedance bandwidth and axial ratio (AR) bandwidth is presented based on characteristic mode analysis (CMA). The circular polarization characteristics are generated by exciting two orthogonal degenerate modes (DMs) via single feeding simultaneously. The 90° phase difference is achieved by loading the lumped inductors or capacitors. The wide bandwidth characteristics are generated by splitting a pair of DMs. Consequently, the two overlapping resonance points are split. The positions of feeding and loadings are determined with the aid of CMA. Compared with conventional methods, the presented method can simplify the feeding structure and provided a compact antenna. Based on this method, a loop antenna with two inductors is demonstrated for circular polarization application. The measured results show an impedance bandwidth of 47% and 3 dB AR bandwidth of 8.3% at 2.4 GHz wireless local area network (WLAN) bands. Both the simulated and measured results agree well.

Compact Dual-Band Dual-Mode SIW Balanced BPF With Intrinsic Common-Mode Suppression

In this letter, a compact dual-band dual-mode substrate integrated waveguide (SIW) balanced band-pass filter (BPF) with intrinsic common-mode (CM) suppression is designed by using a single perturbed SIW circular cavity. The vias and slot perturbations are introduced to tune the resonant modes TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">010</sub> , TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">110</sub> (a pair of degenerate modes), and TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">210</sub> of a circular cavity. Thus, they can be used to form two differential-mode (DM) passbands with independently adjustable center frequencies and bandwidths. The SIW can be seen as a natural balun with intrinsic CM suppression. Furthermore, the planar differential excitation structure is designed to excite the perturbed SIW cavity. The CM noise cannot excite SIW cavity due to the characteristics of hybrid electromagnetic boundary. Finally, a compact dual-band dual-mode SIW balanced BPF at 8 and 10 GHz is designed and fabricated, and the measured results show good agreement with the simulated ones.

Unidirectional emission and nanoparticle detection in a deformed circular square resonator.

We propose a novel deformed square resonator which has four asymmetric circular sides. Photons leak out from specific points, depending on the interplay between stable islands and unstable manifolds in phase space. By carefully breaking the mirror reflection symmetry, optical modes with strong chirality approaching 1 and unidirectional emission can be achieved simultaneously. Upon binding of a nanoparticle, the far-field emission pattern of the deformed microcavity changes drastically. Due to the EP point of the degenerate mode pairs in the deformed cavity, chirality-based far-field detection of nanoparticles with ultra-small size can be realized.

A low‐profile circularly polarized dielectric patch antenna with bandwidth expansion

A new technology for expanding the axial ratio (AR) bandwidth of the circularly polarized (CP) dielectric patch (DP) antenna while maintaining the low-profile characteristic is proposed for the first time. By making full use of the multimode characteristic of the DP resonator, two pairs of degenerate modes (ie, TM101 and TM011, TM121 and TM211) are selected for the broadband design. The key to the proposed technology is that according to the EM field distribution of the two pairs of degenerate modes, four air holes are introduced in the DP and their position and size are elaborately designed to discriminately control the frequency of the two pairs of degenerate modes. Then, these modes become close and are merged to effectively expanding the AR bandwidth of the low-profile CP DP antenna. For demonstration, a prototype centered at about 10 GHz is designed, fabricated, and measured. The measured results exhibit that the proposed CP DP antenna with a low profile of 0.07λ0 owns a 3 dB AR bandwidth of 9.7% and a peak gain of 7.66 dBic. Good agreement is observed between simulated and measured results.

High Isolation and Low Cross-Polarization of Low-Profile Dual-Polarized Antennas via Metasurface Mode Optimization

A low-profile dual-polarized metasurface antenna with high isolation and low cross-polarization is proposed in this communication. The proposed metasurface consists of an array of $4\times 4$ patches. Through characteristic mode analysis (CMA), a pair of degenerate modes is identified to achieve the desired radiation features. By modifying the patches of the metasurface, the strongest mode current distributions of the two modes are moved from the center to the edge of the metasurface. One feed port can efficiently excite only one particular mode, and the other mode cannot be excited simultaneously. Each of the modes are differentially fed using two Y-shaped microstrip lines via two slots. As a result, both high isolation and low cross-polarization can be obtained. The simulation and experimental results show that the proposed antenna achieves not only a low profile of $0.05\lambda _{0}$ (where $\lambda _{0}$ is the free-space wavelength at the center resonant frequency) but also a broad impedance bandwidth of 36% and a high isolation of 53 dB. In particular, the enhanced cross-polarization discrimination (XPD) is lower than −40 dB at the broadside, lower than −33 dB within ±30° of the main lobe, and lower than −28 dB within ±60° of the main lobe.

Dual‐band filter based on one single circular patch resonator with highly improved bandwidths and compact size

In this Letter, a new design of dual-band patch filter is proposed with greatly improved bandwidth and miniaturised size based on one single modified circular patch resonator. In this design, a metallic via is introduced in the centre region of the patch to develop the modified resonant TM01 mode (TM′01 mode), while two types of slot perturbations are adopted to separate a pair of degenerate modes of TM11 (TM11A and TM11B) and control another pair of degenerate modes of TM21 (TM21A and TM21B), respectively. Thus, two passbands with one transmission zero (TZ) can be attained by elaborately exploring these resonant modes (the TM′01 and TM11A modes form up the lower passband while TM11B and TM11A modes constitute the upper passband, and TM21B mode is responsible for the TZ). For verification, one prototype is implemented. Results indicate that the novel dual-band filter (centred at 3.7 and 5.3 GHz) exhibits not only relative compact size (0.36 λ g × 0.36 λ g), but also much larger 3-dB fractional bandwidths (27 and 13%), nice return loss (better than 21 dB) and insertion loss (better than 1.0 dB), compared with other reported patch filters.

Topologically protected edge states of elastic waves in phononic crystal plates

&lt;sec&gt; The topologically protected edge states of elastic waves in phononic crystal plates have the outstanding characteristics in wave manipulation such as the strong suppression of back-scattering and defect immunity, which can be used for controlling vibration and noise, detecting the structural damage, conducting the material nondestructive test and other engineering practices, and therefore have received much attention. But for plate structures, the propagation of elastic waves is complicated due to the coexistence and coupling of different types of wave modes, resulting in a challenge in designing topologically protected states. &lt;/sec&gt;&lt;sec&gt;In this paper, a simple phononic crystal plate with triangular holes is designed for elastic wave manipulation based on topologically protected edge states. The band structure characteristics of the unit cell are studied by varying the rotation angle &lt;i&gt;θ&lt;/i&gt; of the triangular holes around their geometric centers from the initial positions. It is found that the band structure of the initial unit cell with rotation angle &lt;i&gt;θ&lt;/i&gt; = 0° has two pairs of degenerate modes. At &lt;inline-formula&gt;&lt;tex-math id="M6"&gt;\begin{document}$ \theta = \pm 33^\circ $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="15-20200542_M6.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="15-20200542_M6.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;, a double Dirac cone appears at the center &lt;i&gt;Γ&lt;/i&gt; point of the Brillouin zone without requiring the lattices to fold, and a band inversion occurs on both sides of &lt;inline-formula&gt;&lt;tex-math id="M7"&gt;\begin{document}$ \pm 33^\circ $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="15-20200542_M7.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="15-20200542_M7.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; which can be characterized as a topological phase transition. &lt;/sec&gt;&lt;sec&gt;The elastic band gap and two kinds of pseudospin states with clockwise or counterclockwise circulating mechanical energy flux patterns in the band structure are found by calculating the projected band structures of a supercell which is composed of phononic crystals with different topological phases. Based on this finding, different constructions of phononic waveguide are used for implementing the numerical analysis to demonstrate the back-scattering immunity of the edge states when disorder, tortuosity and cavity are introduced into the waveguide. Unidirectional robust propagation and multichannel waveguide switch due to the pseudospin-dependent one-way edge modes are also validated with numerical models. The phononic crystal plate presented in this paper provides a simple realizable method of designing the topologically protected elastic edge states. &lt;/sec&gt;

Pin‐loaded triple‐mode patch resonator for bandpass filter design

AbstractIn this letter, a pin‐loaded triple‐mode square patch resonator is proposed for bandpass filter (BPF) design. By loading short‐circuited pins underneath the patch, the patch resonator not only enables DC‐blocking, but also brings out one additional resonant mode, thus a triple‐mode patch resonator can be formed up under operation with a pair of degenerate modes. According to the field distributions, these three resonant modes can be tuned by virtue of loaded slots and pins, while these two degenerate modes can be properly split by offset‐positioning the two sets of pins. In final, a pin‐loaded triple‐mode patch BPF is designed, fabricated and measured to validate the predicted results.