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Gradient index (GRIN) lenses embody a powerful technology that enables control of electromagnetic wave propagation over wide frequency bands. However, GRIN lenses that achieve multifunctional (i.e., dual broadband) performance have not been realized mainly due to the limitations of conventional techniques such as Transformation Optics (TO). This paper proposes a multi‐objective inverse‐design approach for the optimization of multi‐band GRIN lenses with highly constrained aperture sizes. A candidate lens design is fabricated from a ceramic material using a new additive manufacturing approach allowing for spatially‐varying permittivities between 2–6.5 to be achieved at sub‐cm resolution. Measured results validate the candidate functionalized ceramic GRIN lens's simulated multi‐band performance and demonstrate the efficacy of the proposed inverse‐design procedure. [ABSTRACT FROM AUTHOR]

In this article, bandwidth-controllable suspended patch antennas (SPAs) loaded by anisotropic impedance surfaces (AISs) are proposed. A highly efficient yet accurate semianalytical modal expansion method (MEM) is developed for calculating the input impedance and radiation properties of the proposed antenna, which greatly reduces the simulation time and consumed memory compared to a commercial full-wave solver. The MEM is further utilized by coupling it with a genetic algorithm for effectively performing inverse-design, i.e., optimizing AIS-loaded SPAs with different predefined frequency responses. Three proof-of-concept antenna examples are designed, fabricated, and characterized, including an ultrawideband (UWB) antenna, a dual-wideband antenna, and a band-notched UWB antenna. The operating principle is illustrated by investigating the resonant modes of the AIS-loaded SPAs. The measured results of the three antennas exhibit good agreement with theoretical predictions, demonstrating that all three antennas have vertically polarized conical patterns in the E-plane and omnidirectional patterns in the H-plane with a cross polarization of smaller than −15 dB in their respective operational frequency band(s). The good performance demonstrates that the proposed AIS-loaded SPAs are promising candidates for broadband and multiband communications. [ABSTRACT FROM AUTHOR]

In this article, an efficient transient analysis method with arbitrary high-order accuracy for nonlinear field-circuit cosimulation problems is proposed. The proposed method combines a local time-stepping (LTS) technique with the discontinuous Galerkin time-domain (DGTD) method based on an arbitrary high-order derivatives (ADER) time integration scheme. The stability of the proposed method is not limited by the global time step size, allowing nonlinear and linear elements to update themselves with individual and optimal time intervals in accordance with the local stability condition. It is shown that the efficiency of the proposed method can be significantly improved when the nonlinear effects increase, which requires a smaller time interval to ensure system convergence. Several field-circuit coupling structures are simulated to demonstrate the accuracy and efficiency of the proposed method, confirming that it represents an effective tool for transient analysis of nonlinear field-circuit structures. [ABSTRACT FROM AUTHOR]

In this article, a compact triple-port dual-band triple-mode antenna enabled by a shielded mushroom structure with operational bands centered at 2.4 and 5.8 GHz is proposed possessing both pattern and polarization diversities. By tailoring the dispersive properties of the artificial transmission line (ATL) cells and structuring them into a multilayer architecture, the integrated antenna is capable of generating vertically polarized, $y$ -horizontally polarized, and $x$ -horizontally polarized radiation patterns simultaneously at two predefined bands with good port isolations and field orthogonality. The design concept and the analysis of the ATL cells in the form of shielded mushrooms are described, illustrating the dual-band operating principle of the antenna. A proof-of-concept antenna is designed with a footprint of $0.48\lambda _{0}^{2}$ and a profile of $0.07\lambda _{0}$ , where $\lambda _{0}$ is the free space wavelength at 2.4 GHz. The proposed antenna was fabricated and characterized, achieving measured $S_{11} < - 10$ dB bandwidths of 35 and 85 MHz in the two targeted bands, respectively, with mutual coupling smaller than −15 dB and envelope correlation coefficients below 0.01 for all three ports. Moreover, it is shown that the two operational bands of the antenna can be independently controlled, which reveals the unprecedented degrees-of-freedom in its design. The demonstrated dual-band triple-mode antenna is highly useful for dual-band multimode wireless devices and dual-band multiple-input multiple-out communication systems. [ABSTRACT FROM AUTHOR]

In this work, compact polarization-controllable dual-band antennas are designed, prototyped, and experimentally verified, which are composed of a planar monopole on top of a dual-layer truncated metasurface (MS) containing patches and nonbianisotropic complementary split ring resonators. By tailoring the dispersive properties of the MS, the relative phase difference of resonances associated with surface waves supported along two orthogonal horizontal directions can be independently engineered at two separate frequency bands, thereby giving rise to compact dual-band antennas with controllable polarization in each band. Three proof-of-concept example antennas with a form factor on the order of $0.3\lambda _{\mathbf {0}}\times 0.3 \lambda _{\mathbf {0}} \times 0.04 \lambda _{\mathbf {0}}$ were designed and measured. The first one provides circularly polarized (CP) radiation with the same sense of polarization in both bands, the second one offers linearly polarized (LP) radiation in the lower band and CP radiation in the higher band, while the last one achieves CP radiation in the lower band and LP radiation in the higher band. The measured results agree well with the simulation predictions, thus verifying the proposed concept and specific antenna designs. [ABSTRACT FROM AUTHOR]

In this article, a novel dual-polarized embroidered textile antenna array with an omnidirectional radiation pattern is proposed for both on- and off-body wearable applications. The flexible antenna is composed of a group of circularly oriented dual-polarized patch antennas excited with uniform amplitude and phase. The antenna array can be wrapped around a cylinder, such as an arm or a leg, for realizing a quasi-omnidirectional radiation pattern in the azimuthal plane, which is highly desirable in both on-body and off-body wearable applications. The operating principles and design consideration for how to achieve the omnidirectional radiation and how to avoid radiation nulls are investigated in detail. Moreover, these analytical studies are verified through the experimental results. In addition, a dual orthogonal polarization capability is employed to improve the link reliability. Due to the high front-to-back ratio (FBR) exhibited by each patch antenna element, the proposed omnidirectional antenna array also features a low specific absorption rate (SAR) and high efficiency, which are extremely important for wearable applications. As a proof-of-concept, an antenna array prototype operating at 5.8 GHz is designed, fabricated, and tested. The measured results agree reasonably well with the simulations in terms of S-parameters, polarization isolation, and radiation patterns, demonstrating that the proposed antenna array is ideally suited for potential wearable applications. [ABSTRACT FROM AUTHOR]

A nonconforming mixed-element (tetrahedral/hexahedral) discontinuous Galerkin time-domain (DGTD) method with a perfectly matched layer (PML) absorber is proposed to analyze the electromagnetic scattering from doubly periodic structures. An efficient auxiliary differential equation (ADE)-based PML implementation is presented with transformed field variables introduced by the time-domain periodic boundary conditions (PBCs). The proposed PML implementation performs well in absorbing the waves with high-order Floquet modes. Additionally, a mixed-order DGTD method is introduced to improve the proposed PML implementation’s long-term stability and reduce the total computational cost. Based on the mixed tetrahedral and hexahedral grids, the nonconforming DGTD method can provide accurate field distribution near complex scattering geometries while simultaneously reducing the degrees of freedom (DoF) in the rest of the computational domain, including the open space and PML regions. Finally, electromagnetic simulations are presented to demonstrate the applicability, accuracy, and efficiency of the proposed method. [ABSTRACT FROM AUTHOR]

An efficient, black-box multiobjective optimization technique is presented, which is capable of simultaneously optimizing designs for performance as well as robustness when input tolerance values are not knowna priori. During the optimization process, adaptive statistical surrogate mappings between input variables and output objectives are formulated within a model selection framework. These statistical models can be evaluated in fractions of a second and serve as an efficient surrogate for a more computationally intensive process, such as an electromagnetic simulation. By exploiting the speed offered from surrogate modeling techniques, new, high-performance designs can be quickly identified. In addition, complete tolerance analysis can be conducted within the optimization loop, which provides designers with critical information regarding the robustness of designs. To demonstrate the effectiveness of this approach, it will be applied to the optimization of a capacitively loaded monopole and a wideband Vivaldi antenna. [ABSTRACT FROM AUTHOR]

This paper compares three modern and two classical multiobjective optimizers (MOOs) as applied to real-world problems in electromagnetics. The behavior of sophisticated optimizers on simple test functions has been studied exhaustively. In contrast, the algorithms here are tested on practical applications, where the function evaluations are computationally expensive, making the convergence rate a crucial factor. The examples considered include the optimization of a narrowband slot antenna, a mushroom-type electromagnetic bandgap structure, and an ultrawideband Vivaldi antenna. Another popular topic in the literature is in comparing classical MOOs on electromagnetics problems. The modern optimizers chosen in this paper are state of the art and each has a distinct design philosophy. This paper introduces two unique MOOs to the electromagnetics community: BORG, an auto-adaptive genetic algorithm and the Multi-Objective Covariance Matrix Adaptation Evolutionary Strategy (MO-CMA-ES), an extension of the popular single-objective CMA-ES. These algorithms are compared to the Multi-objective Evolutionary Algorithm based on Decomposition (MOEA/D), a Chebysheff scalarization algorithm, and two classical MOOs. This paper will study the behavior of these algorithms on problems in electromagnetics with a limited number of function evaluations using five distinct metrics and will provide useful guidelines and recommended optimizer settings. [ABSTRACT FROM AUTHOR]

Since the pioneering work of Heinrich Hertz, perfect-electric conductor (PEC) loop antennas for RF applications have been studied extensively. Meanwhile, nanoloops are promising in the optical regime for their applications in a wide range of emerging technologies. Unfortunately, analytical expressions for the radiation properties of conducting loops have not been extended to the optical regime. This paper presents closed-form expressions for the electric fields, total radiated power, directivity, and gain for thin-wire nanoloops operating in the terahertz, infrared and optical regimes. This is accomplished by extending the formulation for PEC loops to include the effects of dispersion and loss. The expressions derived for a gold nanoloop are implemented and the results agree well with full-wave computational simulations, but with a speed increase of more than $300\times $ . This allows the scientist or engineer to quickly prototype designs and gain a deeper understanding of the underlying physics. Moreover, through rapid numerical experimentation, these closed-form expressions made possible the discovery that broadband superdirectivity occurs naturally for nanoloops of a specific size and material composition. This is an unexpected and potentially transformative result that does not occur for PEC loops. Additionally, the Appendices give useful guidelines on how to efficiently compute the required integrals. [ABSTRACT FROM AUTHOR]

A compact circularly polarized (CP) co-designed filtering antenna is reported. The device is based on a patch radiator seamlessly integrated with a bandpass filter composed of coupled stripline open-loop resonators, which are designed together as a system. In the proposed design, the patch functions simultaneously as the radiator and the last stage resonator of the filter, resulting in a low-profile integrated radiating and filtering module with a small overall form factor of \mathbf0.53\lambda _0 \times 0.53\lambda _0 \times 0.07\lambda _0. It is shown that the filtering circuit not only ensures frequency selectivity but also provides impedance matching functionality, which serves to broaden both the impedance and axial ratio bandwidths. The designed filtering antenna was fabricated and measured, experimentally achieving an $\mathbf{{S_{11}} < - 13.5\;dB}$, an axial ratio of less than 3 dB and a gain higher than 5.2 dBi over a bandwidth from 3.77 to 4.26 GHz, i.e., around 12.2%, which makes it an excellent candidate for integration into a variety of wireless systems. A linearly polarized version of the integrated filtering antenna was also demonstrated. In addition, further full-wave simulations and experiments were carried out to verify that the designed CP filtering antenna maintains its properties even when mounted on different positions of the human body with various body gestures. The stable impedance and radiation properties also make it a suitable candidate as a wearable antenna for off-body wireless communications. [ABSTRACT FROM PUBLISHER]

The introduction of electromagnetic (EM) media with unique field manipulation properties, collectively labelled as metamaterials, has boosted the interest toward the design, the fabrication, and the testing of artificial materials whose features can be engineered according to the applicative requirements and user objectives. In this framework, the long-term promise of reconfigurable metamaterial theory (i.e., the possibility to change the EM response of a 2-D/3-D material arbitrarily and in real time) has given the designers an extremely wide number of new degrees of freedom for the synthesis of innovative adaptive systems. Moreover, successful experimental validations of reconfigurable metamaterials in the entire EM spectrum from microwaves to optical frequencies have further stimulated academic and industrial interests in developing devices with enhanced performances, efficiency, and robustness. Nevertheless, the exploitation of reconfigurable metamaterials in commercial devices is still an open problem with several challenges from both the theoretical and technological viewpoints. This paper is then aimed at reviewing the latest advances on reconfigurable metamaterial engineering from the methodological perspective also providing a comprehensive and balanced survey on latest concepts, current trends, and envisaged future developments on this active field of research. [ABSTRACT FROM PUBLISHER]

A high-gain reduced-profile antenna is designed by combining the effects of a near-zero-index volumetric metamaterial lens and an artificial magnetic conducting (AMC) ground plane. The AMC/metalens antenna design presented here has 20% reduced height over an equivalent metalens antenna with conventional metallic ground plane at the cost of reduced peak directivity and pattern bandwidth. Both the metamaterial unit cells and the mushroom-type AMC structure are designed independently and retuned in the presence of the other for optimal performance. The lens collimates the electromagnetic radiation of a dipole feed by refraction as well as via a Fabry-Perot cavity effect, with resulting gain and patterns that are better than either mechanism can achieve individually. Full wave simulations of the entire metamaterial and AMC structure with a feed dipole agree well with measurements of the fabricated design. [ABSTRACT FROM PUBLISHER]

Metamaterials have been used in many different configurations to enhance the radiation properties of antennas. However, the vast majority of these metamaterial applications only consider linearly polarized antennas. This paper discusses the theory, design, implementation, and measurements of a far-field collimating lens for use with a circularly-polarized crossed-dipole antenna constructed from a 3D-volumetric metamaterial slab. Zero-index materials (ZIM) and low-index materials (LIM) cause the magnitude and phase of the radiated field across the face of the lens to be distributed uniformly, increasing the broadside gain over the feed antenna alone. Full-wave simulations were used in design of the lens, and a prototype metamaterial lens (meta-lens) was constructed and measured to verify the theoretical predictions. The meta-lens was found to increase the measured directivity of a crossed-dipole feed antenna by more than 6 dB, in good agreement with numerical simulations. [ABSTRACT FROM PUBLISHER]

A new method of optimization recently made popular in the evolutionary computation (EC) community is introduced and applied to several electromagnetics design problems. First, a functional overview of the covariance matrix adaptation evolutionary strategy (CMA-ES) is provided. Then, CMA-ES is critiqued alongside a conventional particle swarm optimization (PSO) algorithm via the design of a wideband stacked-patch antenna. Finally, the two algorithms are employed for the design of small to moderate size aperiodic ultrawideband antenna array layouts (up to 100 elements). The results of the two electromagnetics design problems illustrate the ability of CMA-ES to provide a robust, fast and user-friendly alternative to more conventional optimization strategies such as PSO. Moreover, the ultrawideband array designs that were created using CMA-ES are seen to exhibit performances surpassing the best examples that have been reported in recent literature. [ABSTRACT FROM PUBLISHER]

Design of stacked-patch antennas using magneto-dielectric substrates was investigated. In particular, special types of substrates with identical relative permittivity and permeability were considered. The optimal design parameters were determined using a genetic algorithm. It will be shown that by employing these matched magneto-dielectric substrates, a significant miniaturization of up to 60% can be achieved while providing a large operating bandwidth (20%). Several design examples were considered and their performance was evaluated using a full-wave analysis technique based on the method of moments. The tradeoff between antenna gain and degree of miniaturization for a fixed bandwidth was also investigated. A fabrication methodology for obtaining the required matched magneto-dielectric substrate materials is also proposed. [ABSTRACT FROM AUTHOR]