Wideband Dielectric Resonator Antenna With Linear and Circular Polarization Diversity for UAV Applications

Abstract This work presents a comprehensive Finite-Difference Time-Domain (FDTD) study of the multiband optical response and light-harvesting characteristics of Cu@TiO2 core–shell nanoparticles. By systematically varying the copper core radius and TiO2 shell thickness, the interplay between plasmonic and dielectric resonances is quantitatively elucidated. The hybrid nanostructure supports three distinct optical modes: an ultraviolet interband transition and two visible-range hybridized plasmon resonances arising from bonding and antibonding coupling between the Cu core plasmon and TiO2 shell polarization. Increasing the shell thickness or core radius enhances the spectral overlap with the solar spectrum, yielding up to an order-of-magnitude improvement in absorbed photon flux and hot-carrier generation compared with a dielectric reference. The optimized configuration achieves a high refractive index sensitivity of ~120 nm/RIU, indicating strong field confinement and efficient plasmon–dielectric interaction. The consistent enhancement in the spectral overlap integral (Γ), absorbed photon flux (APF), and hot-electron injection rate demonstrates that shell-thickness and core-size engineering offer powerful routes to tailor optical absorption, carrier generation, and sensing performance. These findings establish Cu@TiO2 as a cost-effective, broadband-active alternative to noble-metal hybrids for plasmon-enhanced photocatalysis and optical sensing applications.

ABSTRACT Metasurfaces represent a class of artificially engineered planar optical devices that achieve exceptional functional performance through optimized nanostructure design and array configurations. These devices have emerged as the predominant methodology for developing integrated, compact optical systems, offering micro‐ and nano‐scale solutions that enable comprehensive multidimensional optical modulation. Here, we report a full‐space switchable optical encryption platform exhibiting wavelength‐dependent information control. Through precisely engineered nanostructures, the system demonstrates three distinct operational regimes: selective reflection revelation without transmission, complete concealment of real‐space information via dual‐holographic encryption, and switchable recovery of both real‐ and k ‐space manifestations across transmission and reflection modes. Spectroscopic characterization and computational modeling reveal the critical role of dielectric nanopillar resonance in enabling these switchable states. This work establishes a paradigm for active optical security devices with potential applications in anti‐counterfeiting, optical communication, switching, and information encryption technologies.

Abstract A compact dual-port Dielectric Resonator Antenna designed for 5G millimeter-wave bands is proposed. The antenna employs a single rectangular DRA with two orthogonal feeding ports to achieve polarization diversity and minimize port-to-port coupling. A central notch is incorporated within the resonator to achieve dual-wide impedance bandwidth. The gain of the DRA is enhanced by increasing the profile to excite it in higher order modes. To further improve isolation between the orthogonal ports, a corner-placed defected ground slot is incorporated in combination with metallic strips attached to the resonator sidewalls. Unlike conventional dual-port DRAs, the proposed configuration incorporates orthogonal aperture coupling, a central notch, and a combination of isolation techniques to achieve the desired performance. The proposed antenna covers the dual bands of 24.45–30.23 GHz (21.1%) and 32.25–41.17 GHz (24.3%). It demonstrates an inter-port isolation exceeding 40 dB, peak realized gain higher than 7 dB, and maintains radiation efficiency above 93%, all within a compact footprint of 1.75 λ o × 1.75 λ o × 0.49 λ o . Owing to its compactness, dual-wideband capability, strong isolation, and efficient radiation, the proposed antenna offers a promising solution for fifth-generation mm-wave communication systems.

The twisted-pair (TP) coil design is a promising strategy for developing novel, flexible, wearable MRI detectors that can provide SNR gains in various clinical applications of high-field MRI. We hypothesize that the TP coil's receive (Rx) sensitivity can be significantly increased by combining it with two complementary elements, such as dielectric resonators (DRs) and dipole antennas. TP coils were combined with DRs made of high-permittivity material (εr = 1070) and transceiver (TxRx) dipole antennas. The Tx and Rx performance of six different types of arrays (TP-only, dipole-only, TP with DRs, dipole with DRs, dipole with TPs, and dipole with TPs and DRs) was investigated through numerical simulations involving a cylindrical phantom suitable for lower extremity applications and two human voxel models. MR phantom experiments were conducted using a 7 Tesla whole-body MRI scanner to validate the Tx and Rx performance of all six array types. The array combining all three types of elements (TP coils, DRs, and dipole antennas) provided the highest overall Rx performance; MR phantom experiments showed that integrating DRs with TP coils increased peripheral SNR by 250% and central SNR by 23% (for a total 38% gain in the center when also using dipole antennas in Rx). Human voxel model simulations confirmed that similar SNR gains can be achieved in vivo. Integrating DRs into TP coils also increased central Tx field efficiency by 4.6% and reduced the peak SAR10g by 25.8% in the human voxel model Hugo. DRs and dipole antennas can significantly improve the overall Rx performance of TP coils. This concept can benefit MRI of the human lower extremity at 7 Tesla and encourage exploration of its utility for other clinical applications.

ABSTRACT Integrated sensing and communication (ISAC) is a key technology for next‐generation cognitive radio (CR) systems that allows for the smooth coexistence of several wireless services and effective spectrum utilization. A comprehensive review of current developments in ISAC antenna configurations specifically designed for CR applications is provided in this article. The significant representations of CR architecture are dielectric resonator antenna (DRA)‐based CR systems and microstrip patch antenna (MPA)‐based CR systems. A communication and sensing antenna enables CR antennas to perform multiple purposes. The communication antenna, which is combined with a reconfigurable filter, offers narrowband operation for dependable data transmission, while the sensing antenna, which is usually constructed as an ultrawideband (UWB) structure, allows spectrum awareness by collecting a wide range of frequencies. The study covers key design approaches, reconfigurability strategies, and trade‐offs related to ISAC antennas in CR systems, focusing on their use in adaptive wireless communication and dynamic spectrum access. The review paper also addresses the design, challenges, and performance parameters of CR.

We combine differential scanning calorimetry, broadband dielectric spectroscopy, and 1H and 2H nuclear magnetic resonance (NMR) for component-selective studies of molecular reorientation and diffusion in mixtures comprising the dipeptide N-acetyl-glycine-methylamide (NAGMA), which is commonly considered as a protein-backbone model, and deuterated water in a broad temperature range of 140-340 K. For a 7.5m NAGMA-D2O mixture, crystallization is largely avoided, revealing a separation of the dipeptide-dominated α process, which describes the glassy slowdown, from the water-caused ν process. The latter shows a dynamical crossover at Tg = 175 K and thermally activated motion governed by a temperature-independent Gaussian-like distribution of activation energies with a mean value of Em = 0.49eV and a standard deviation of σE = 0.035eV in the glassy state. Detailed NMR analyses show that, despite the time-scale separation, rotational-translational coupling is found for water dynamics at least down into the weakly supercooled regime. Moreover, NMR reveals that the ν process involves a quasi-isotropic reorientation of basically all water molecules even below Tg, while slow or restricted water reorientation does not occur. Based on our findings, we discuss the temperature-dependent coupling of the dipeptide and water motions. For a 2m NAGMA-D2O mixture, partial crystallization leads to an enhanced temperature dependence. Disentangling the rotational motions of the liquid and crystalline water fractions, we find that the liquid fraction exhibits Arrhenius behavior with Ea = 0.89eV until a dynamical crossover again occurs upon cooling, while the reorientation of the ice fraction highly resembles that in hexagonal bulk ice.

This paper presents a compact, wideband, high-gain circularly polarized (CP) hemispherical dielectric resonator antenna (HDRA) designed for millimeter-wave 5G applications. The proposed antenna employs a linearly polarized (LP) HDRA excited through an annular slot coupled to a 50-Ω microstrip feed, enabling efficient radiation at millimeter-wave frequencies. Wide impedance bandwidth from 20 to 28 GHz is achieved by overlapping multiple adjacent resonant modes of the HDRA. Circular polarization is realized by introducing a frequency-selective surface (FSS) superstrate positioned at an optimized distance above the antenna. To further enhance the axial-ratio bandwidth and gain, a 2 × 2 HDRA array with a sequential-phase feeding network and an additional dielectric superstrate is implemented. The antenna is fabricated and experimentally validated. Measured results demonstrate an impedance bandwidth of 33.3% (20–28 GHz), a peak realized gain of 11.8 dBi, and a 3-dB axial-ratio bandwidth of 31% (20.5–28 GHz). The proposed design offers a compact and efficient solution for millimeter-wave 5G and IoT applications.

Horizontally and Circularly Polarized Omnidirectional Filtering Dielectric Resonator Antenna

Microscale patterning of delicate materials such as colloidal nanoparticle monolayers, solvent-swollen polymer substrates, and 3D resonators in millimeter/terahertz (mm/THz) dielectric metasurface remains a formidable challenge for conventional photolithography. Overcoming these limitations is critical for the next generation of wearable electronics, photonic devices, and metamaterials. Here, a versatile strategy using photocurable perfluoropolyether (PFPE) is introduced to create high-precision, reusable soft template guided by predesigned photomasks. These templates enable non-destructive, high-fidelity transfer of diverse functional materials including metal films, composites, and nanoparticle monolayer onto a wide range of substrates. Remarkably, the PFPE template can be reused multiple times without compromising patterning fidelity, offering a cost-effective solution for large-scale manufacturing. Beyond general microscale patterning, this approach provides unprecedented control over 3D dielectric resonators in mm/THz all-dielectric metasurfaces, delivering superior electromagnetic performance. With its combination of precision, reusability, and adaptability to various surfaces, this method opens exciting opportunities for microscale fabrications across flexible electronics, advanced photonics, and metasurfaces, redefining what is possible with soft-template patterning.

C-band dielectric resonator antenna with novel ultralow tanδ and temperature stabilized LaTmO3 microwave dielectric ceramics

Bi-doped performance-enhanced LaBO3 microwave dielectric ceramics for dielectric resonator antennas with leaky mode

A Dual-Polarized Stacked Dielectric Resonator Antenna Array with Extremely Low Mutual Coupling for 6G Base Stations

Background. One of the promising elements of optical and quantum communication systems is various delay lines built on the high-quality dielectric resonators (DRs). These lines typically comprise a substantial number of elements, making the optimisation of their parameters quite challenging. The theory of DRs serves as a foundation for comprehending, calculating, and optimising the parameters of delay lines and other devices, facilitating a considerable reduction in the computational resources that typically require the use of powerful computers. Objective. The study aims to derive analytical expressions for the electromagnetic parameters of diverse optical waveguides, composed of numerous types of DRs, to utilise them as transmission lines for optical communication systems. To address this issue, an infinite linear system of equations has been derived based on the perturbation theory applied to Maxwell's equations, which connects the complex amplitudes, wave numbers and the resonator frequencies. Methods. To derive solutions for the analytical expressions, perturbation theory and the theory of infinite linear equations are employed. The outcome is a set of new general analytical formulae that describe the dispersion curves of lattices made up of an infinite number of various types of DRs. Results. A theory of wave propagation in systems of interconnected one-, two-, and three-dimensional lattices of DRs extended infinitely in one or more directions has been developed. New analytical expressions for the dispersion characteristic of eigenwaves, delay times, and distributions of complex amplitudes of resonators, without any limitations on their quantity, have been derived. By utilising perturbation theory, a novel analytical model has been developed that describes the eigenwaves of three-dimensional lattices composed of identical ring structures of DRs. General analytical solutions for frequency dependencies and amplitudes for one-, two-, and three-dimensional lattices with varying arrangements of resonators have been identified. Conclusions. The developed theory serves as the foundation for the analysis and design of many devices operating within the optical wavelength spectrum, constructed upon an infinite variety of distinct types of DRs. The obtained new analytical expressions for calculating optical waveguide parameters, based on coupled oscillations of DRs, enable the development of innovative and more efficient mathematical models for various optical communication devices.

Abstract An advanced isolation control technique is proposed for a terahertz (THz) multi-input multi-output (MIMO) antenna, significantly enhancing port-to-port isolation. This approach utilizes a silicon-based dielectric resonator antenna for high-performance tunable THz MIMO system. The design follows a structured evolutionary process, beginning with a dual-feed (DF) configuration without a dielectric resonator as the baseline model. Enhancements were introduced by incorporating a graphene metal coating, improving tunability and isolation. Further refinements involved integrating a split square ring resonator without an RDRA, enhancing isolation and polarization characteristics. The design was then optimized by introducing a metal-coated RDRA, improving gain, radiation efficiency, and circular polarization purity. Additionally, a complementary split ring resonator-loaded circularly polarized DF structure was incorporated for further performance enhancement. The proposed MIMO antenna achieves 25.5 dB isolation at 7.2 THz without a metal coating. By applying a graphene coating, isolation increases to 49 dB at 7.42 THz, using graphene’s tunable conductivity under an external DC bias for dynamic reconfiguration. The antenna exhibits excellent pattern diversity, with an envelope correlation coefficient below 0.003 and a diversity gain of 9.94 dB. Further isolation improvement is achieved by integrating a split-ring resonator on the dielectric material, enhancing isolation up to 59 dB. These advancements make the proposed antenna highly suitable for THz applications.

Wideband graphene-based THz metasurface absorber with cylindrical dielectric resonator for biomedical refractive index sensing

Bound states in the continuum (BICs) offer an exceptional platform for wave trapping. Quasi-BICs in an isolated dielectric resonator with high quality factors (Q-factors) can be realized through leveraging avoided crossing between two modes due to strong coupling arising from destructive interference. In this work, we present a general strategy for constructing quasi-BICs in dimer dielectric resonators, achieving Q-factors that are enhanced by two to tens of times compared to quasi-BICs in a single dielectric resonator. Starting from a single dielectric structure supporting quasi-BICs, we optimize the Q-factors of supercavity modes by introducing an air gap within the single structure and systematically varying several structural dimensions of the dimer configuration. Multipole decomposition indicates that the enhancement in Q-factors originates from the suppression of multiple radiation channels. Moreover, we demonstrate that the design approach is universal via investigating high-Q quasi-BICs in both one-dimensional (1D) dimer rectangular nanowires (NWs) for transverse electric (TE) and transverse magnetic (TM) polarizations and three-dimensional (3D) dimer cuboids. Additionally, we explore the potential for further increasing the Q-factors of quasi-BICs using a trimer-resonator system. This work provides a rational framework for designing ultrahigh-Q resonances based on dimer or trimer dielectric resonators, with promising applications for enhancing light-matter interactions.

Enhancing the spontaneous and stimulated emission rates of magnetic quantum emitters through the Purcell effect is essential for designing high-performance quantum devices based on high quality factor and small mode volume. At room temperature, structures constructed using high-index dielectric materials have been favored due to their ability to effectively confine electromagnetic fields. However, these dielectric resonators are plagued by an inherent sensitivity to thermal variations, which are unavoidable during the optical excitation or readout of the quantum states. Here, we propose to solve this issue with a dielectric-free, all-metallic toroidal split-ring resonator cluster of subwavelength size (≤λm/17), which exhibits a fundamental magnetic mode at approximately 1.45 GHz (λm ~ 207 mm) and a remarkably low mode volume (8.1times 1{0}^{-6}{lambda }_{{{{rm{m}}}}}^{3}). Through experimental investigations, we demonstrate that the proposed resonator exhibits a high Purcell factor (5 × 106), and observe maser action when paired with a pentacene-based gain medium. We evidence the remarkable stability of the output pulse against thermal variations caused by thousands of consecutive optical excitations, by far surpassing that of masers based on dielectric resonators.

This paper outlines the design and characterization of a dual-port dielectric resonator antenna made from alumina (Al₂O₃) and coupled with a metasurface superstrate for millimeter-wave applications. Alumina ceramic with high permittivity (εr = 9.9, tanδ = 0.0019) was employed to excite the lower-order HEM11δ mode through aperture coupling to enable efficient radiation between 27.65 and 28.75GHz. A dual-stub C-shaped slot was carefully engineered on the substrate to generate orthogonal modes, thereby realizing circular polarization throughout the bandwidth of 27.8-28.45GHz. To access better radiation properties, a double-negative (DNG) metasurface lens made on an RT Duroid substrate was coupled with a resultant increase in realized gain to about 11 dBi, with preservation of impedance and polarization properties. Experimental characterization confirmed steady broadside radiation patterns with low mutual coupling (<- 25 dB), together with exemplary diversity parameters (ECC < 0.02, DG ≈ 10 dB). The integration of both dielectric ceramic and metasurface building materials demonstrates a synergistic building-structure approach to realizing high-gain, circularly polarized, volume-reduced radiators with millimeter-wave applications. These outcomes highlight engineered dielectric-metasurface architectures as a prospective pathway for licensed 5G FR2 frequency band.

Abstract In this article, a circularly polarized dielectric resonator antenna (DRA) array with conformal characteristics and improved specific absorption rate (SAR) has been proposed for X-band applications. The proposed structure has been fed through the corporate feed network which excites a radiating mode inside DRA, i.e., $TE_{1\delta1}$ . This mode has been utilized to enhance the impedance bandwidth which is below −10 dB for both the E- and H-plane so as to meet the requirements of next-generation defense communication and low-cost satellite systems. To generate the axial ratio (AR), the extended off-set feed has been employed to provide the required 90 $^{\circ}$ phase shift. Further, in order to enhance the gain and reduce the SAR, an electromagnetic band gap structure has been used as a reflector. Furthermore, multiple arrays have been introduced to extend the coverage area through beam-forming. The proposed design has been fabricated for the experimental validation. The measured IBW and ARBW is 34.74% and 12.2%, respectively. The gain is 10.1 dBic throughout the band of operation along with the radiation efficiency above 85% in various bending conditions. The SAR is much below the permissible limit of 1.6 W/kg. Thus, the proposed array is compact, and it clearly achieves a smaller footprint, better IBW, ARBW and a low SAR with potential prospect for X-band purposes.