Full-wave Analysis Research Articles

A 60-channel high-density flexible receive array for pediatric abdominal MRI.

Conventional MRI coils offer suboptimal parallel imaging performance for young children. Our goal was to enhance imaging acceleration by dedicated, flexible high-density coil design for pediatric patients at 3T. We design, construct, and evaluate a highly flexible small loop array. Key design notes include full-wave simulation and analysis of the dual-turn loop, miniature feedboard allocation at the loop center, and cable management. Phantom experiments and adult and pediatric volunteer case studies were conducted to evaluate the small loop array imaging performance compared to commercial reference coils. Dual-turn loop configuration forms higher preamp decoupling impedance than the same size single-turn, supporting a flexible form factor that requires a wide range of critical overlap. Both phantom and in-vivo studies demonstrate superior parallel imaging performance or high spatial resolution imaging using the small loop, compared to commercial reference coils. A dedicated high-density coil array with a minimum inter-component interference layout design allows a flexible form factor and higher imaging accelerations. Phantom and in-vivo volunteer case studies demonstrate promising results in improving efficiency for pediatric patients in routine clinical imaging procedures.

Efficient Full-Wave Analysis of Lens Antennas with Arbitrary Feeder

Efficient Full-Wave Analysis of Lens Antennas with Arbitrary Feeder

Influence of resonant plasmonic nanoparticles on optically accessing the valley degree of freedom in 2D semiconductors

The valley degree of freedom in atomically thin transition metal dichalcogenides, coupled with valley-contrasting optical selection rules, holds great potential for future electronic and optoelectronic devices. Resonant optical nanostructures emerge as promising tools for controlling this degree of freedom at the nanoscale. However, their impact on the circular polarization of valley-selective emission remains poorly understood. In our study, we explore a hybrid system where valley-specific emission from a molybdenum disulfide monolayer interacts with a resonant plasmonic nanosphere. Contrary to the simple intuition that a centrosymmetric nanoresonator mostly preserves the degree of circular polarization, our cryogenic experiments reveal significant depolarization of the photoluminescence scattered by the nanoparticle. This striking effect presents an ideal platform for studying the mechanisms governing light-matter interactions in such hybrid systems. Our full-wave numerical analysis provides insights into the key physical mechanisms affecting the polarization response, offering a pathway toward designing novel valleytronic devices.

Symmetric CRLH-TL filter based dual band microstrip antenna design approach

This paper presents a novel filter-based analysis for the conventional rectangular patch antenna (RPA) using the Composite Right/Left-Handed Transmission Line (CRLH-TL) theory. We introduce two circuit models for RPA, described by lumped components and transmission line (TL) elements. An RPA is considered a Symmetric CRLH-TL (SCRLH-TL). We validated the analysis by comparing the circuit model and full-wave analysis simulation results. The TL circuit model error in the full-wave analysis was less than 5%. A dual-band Zeroth-Order Resonant (ZOR) antenna is designed and manufactured based on the introduced Lumped element circuit model, which exhibits filtering characteristics in both bands. We obtain the antenna circuit model by incorporating the RPA lump circuit model with LC resonators. We implemented the antenna structure by combining the RPA and complementary split-ring resonators (CSRR) modeled by the LC resonators. We initialized the antenna center frequency bands for WiMAX 2.45 GHz and 3.60 GHz. The CSRRs control the configuration of the center frequencies. The simulation and measured results are in good agreement. The proposed antenna dimensions are 0.66×\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ imes$$\\end{document}0.66×\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ imes$$\\end{document}0.012 λg\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\lambda _g$$\\end{document} at 2.45 GHz (43.22×\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ imes$$\\end{document}43.22×\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ imes$$\\end{document}0.81 mm3). The measured gains are 3.47 dB and 4.64 dB for 2.45 GHz and 3.60 GHz, respectively. Two radiation nulls were observed at 2.09 GHz and 2.98 GHz for the 2.45 GHz band and one radiation null at 3.45 GHz for the 3.60 GHz band. Also, the fractional bandwidth is 4.03% and 1.39%, respectively. The radiation pattern is nearly omnidirectional. The simulated efficiency is 90% for 2.45 GHz and 87% for 3.60 GHz frequency bands.

Full-Wave Analysis of Thermal Noise in Antenna Arrays on Top of Layered Medium

Full-Wave Analysis of Thermal Noise in Antenna Arrays on Top of Layered Medium

Design of HTS linear phase bandpass filter based on the inline topology

Abstract Inline topology filters have the advantages of a simple structure and fewer coupling coefficients. Based on the inline topology, this paper constructs a phase compensation topology of the filter, which can independently and controllably introduce two types of transmission zeros (TZs), and is convenient to realize the Chebyshev-like function response and compensate group delay. The finite frequency transmission zero is directly introduced through the source and load (S/L), and the real zero point is introduced and adjusted through the cross-coupling unit of the main path in this inline phase compensation topology. The two types of TZs can be introduced and regulated independently, so the side-band suppression and group delay compensation can be freely adjusted. A High-temperature superconducting (HTS) filter with inline is designed and processed with a typical structure based on application requirements. The filter introduces two pairs of symmetrical real TZs to improve sideband rejection and a pair of real TZs to control group delays to realize the linear phase. In addition, it has a small size and straightforward construction, and the results of the full-wave analysis method and the theoretical analysis approach match well with the measured results of the frequency response characteristics.

Recent Advances in Reconfigurable Electromagnetic Surfaces: Engineering Design, Full-Wave Analysis, and Large-Scale Optimization

Recent Advances in Reconfigurable Electromagnetic Surfaces: Engineering Design, Full-Wave Analysis, and Large-Scale Optimization

Thin film resonant metasurface absorbers using patch-based arrays on liquid crystal polymer substrates for centimeter-wave applications

This paper reports the design and development of thin-film resonant absorbers for narrowband and multiband operation in the frequency regions centered at 10 GHz. The structure of the resonant metasurface absorber (RMA) is based on a liquid crystal polymer (LCP) thin-film spacer with a copper patch array on the front surface and un-patterned copper film on the back surface of the LCP film. The design and simulation works were carried out using full-wave analysis of the RMA characteristics. The copper-based periodic patch array acts as a metasurface. The perfect RMA for a given LCP film thickness can be obtained through impedance optimization by adjustment of the dimensions of the lattice periods. The electric and magnetic field distributions were studied. The resonant film absorber based on a 100 μm thick LCP film has an electrical thickness of λ/300 at 10 GHz. The experimental work was conducted using a narrowband RMA prototype consisting of 11×11 cells. The measured result of the resonant absorption is at 10.1 GHz, which is in close agreement with the design frequency of 10 GHz. For multiband functionality, double- and quad-band film resonant absorbers have been designed based on a coplanar supercell utilizing the superposition of the resonance effect. The LCP film-based absorbers have the potential to be used in EM shielding and sensing applications in centimeter-wave applications.

Analysis of Reader Orientation on Detection Performance of Hilbert Curve-based Fractal Chipless RFID Tags

The role of the orientation of the radio frequency identification (RFID) reader is vital in the RFID-based communication system. This study presents the design and analysis of the impact of the orientation of the RFID reader (angle of incidence of the plane wave) on the detection and sensitivity characteristics of fractal chipless RFID tags. Four fractal (irregular) shaped tags are developed using four iterations of the Hilbert curve filling algorithm. The full-wave EM analysis of the designed tags in Matlab is performed by exporting them in Computer Simulation Technologies Micro-Wave Studio (CST MWS) in the frequency range of 2 to 20 GHz. Firstly, the performance of the tags is analyzed by observing the radar cross-section (RCS) of the tag for the fixed orientation of the incident plane wave in three different polarizations (horizontal, vertical, and oblique). Later, the variations in the EM spectrum (RCS results) are analyzed for oblique polarization by varying the incidence plane wave in both elevations (for two cases of 0∘ and 90∘) and azimuth planes (sweeping from 0∘ to 180∘ with a step size of 10∘). The analysis of the proposed aggregated RCS response for all cases in oblique polarization produces higher coding capacity (169 bits), coding spatial capacity (16.504 bits/cm2), coding spectral capacity (9.826 bits/GHz), and coding density (0.960 bits/GHz/cm2) for the realized highly irregular tag using fourth-iteration (4T) of Hilbert curve filling algorithm. The proposed procedure of detection based on aggregated response makes the developed RFID communication system more secure and reliable.

Research on the efficient EM modeling method from multilayered anisotropic medium-metal composite targets

The paper presents a high-frequency modeling approach tailored for the electromagnetic (EM) scattering characteristics from electrically large radar targets coated with multi-layered anisotropic mediums (MLAMs). The approach begins by deriving the plane-wave spectrum expression for the incident EM field within MLAMs. It then employs spectral domain full-wave analysis method (SDFWAM) to obtain an analytical representation of the scattering field, further leveraging saddle point evaluation (SPE) to derive asymptotic solutions in the spatial domain. By integrating principles of physical optics (PO) and the tangent plane approximation, the far-field scattering characteristics of target enveloped in the specified medium are efficiently delineated. Validations against standard structure and the Misty satellite model reveal the method's pronounced alignment with the method of moments – finite element method (MoM-FEM) hybrid numerical algorithm, underscoring its notable computational efficiency. Furthermore, in conjunction with scattering sources decomposition technique, the approach is applied to optimize the radar cross-section (RCS) of the Su-57 aircraft, achieving precise and intelligent RCS control at minimal material cost. In conclusion, this research offers pivotal technological and theoretical foundations for EM scattering prediction, stealth design, and performance assessment in radar target domains.

Slot fed circularly polarized magneto-electric dipole antenna array fed by optimized printed microstrip gap waveguide network

<p>A compact, circularly polarized 8 × 8 antenna array is designed for the 60 GHz band. The array comprises circularly polarized magneto-electric dipoles (CP-ME-Dipole) excited by narrow slots. The slots are fed by a printed gap waveguide (PGWG) cooperative network optimized based on the termination of the effective impedance of the array elements. Thus, it accounts for the space mutual coupling of the antenna elements. A procedure based on the full-wave analysis of a 4 ´ 4 array is used to estimate each element’s 8 × 8 array effective port impedance. The cooperative feeding network is designed based on the known effective impedances. The array is divided into two half subarrays out of phase from each other, and a rectangular waveguide feeds both sides. The commonly measured bandwidth of 18.3% achieves return loss better than 10 dB and an axial ratio below 3 dB (AR) of less than 3 dB. A maximum gain of 26.2 dBic with a high radiation efficiency of 82% radiation efficiency.</p>

Slot fed circularly polarized magneto-electric dipole antenna array fed by optimized printed microstrip gap waveguide network

<p>A compact, circularly polarized 8 × 8 antenna array is designed for the 60 GHz band. The array comprises circularly polarized magneto-electric dipoles (CP-ME-Dipole) excited by narrow slots. The slots are fed by a printed gap waveguide (PGWG) cooperative network optimized based on the termination of the effective impedance of the array elements. Thus, it accounts for the space mutual coupling of the antenna elements. A procedure based on the full-wave analysis of a 4 ´ 4 array is used to estimate each element’s 8 × 8 array effective port impedance. The cooperative feeding network is designed based on the known effective impedances. The array is divided into two half subarrays out of phase from each other, and a rectangular waveguide feeds both sides. The commonly measured bandwidth of 18.3% achieves return loss better than 10 dB and an axial ratio below 3 dB (AR) of less than 3 dB. A maximum gain of 26.2 dBic with a high radiation efficiency of 82% radiation efficiency.</p>

High‐gain W‐band‐printed antenna on flexible substrate

SummaryThis article demonstrates a novel type of series‐fed planar antenna array for a W‐band (70 GHz) application. The proposed architecture is a 5‐element antenna array with 10 numbers of gap‐coupled parasitic patches in microstrip configuration over a thin, flexible and bio‐compatible substrate named LCP (liquid crystal polymer). A detailed design methodology with all fabrication constraints has been elaborated on here. Full wave analysis of the whole structure has been carried out in the FEM‐based 3D electromagnetic (EM) solver ANSYS HFSS Suite V.19.2. Parametric simulations were studied to achieve the optimized values of all design parameters. Further, an empirical electrical equivalent circuit model is proposed for the antenna array, and it was validated with the simulation results obtained from the FEM solver. Two prototypes have been fabricated, and measurements were carried out to fetch all the designed antenna parameters. The proto version of the antenna offers peak directive gain of about 19 dBi with better than 22 dB of return loss and 80% radiation efficiency for the frequency range of 67–85 GHz. Experimental and simulated results closely match each other. Small deviations are attributed to practical imperfections incurred by fabrication tolerances, measurement inaccuracies, testing, assembly‐related issues and so forth. Finally, the current research work is compared with the recently reported literature.

An efficient and accurate semi-analytical matching technique for waveguide-fed antennas

Several RF and microwave radiating devices, such as horn antennas, Fabry–Perot cavity antennas, and aperture-fed focusing devices, are excited through rectangular waveguides. The impedance matching of the overall system (from the waveguide feed to the radiating aperture) is a task of crucial importance that is often addressed by means of brute-force parameter-sweep full-wave analyses or blind optimization algorithms. In both cases, a significant amount of memory and time resources are required. For this purpose, we propose here a simple, yet effective solution, which only requires a single full-wave simulation and a semi-analytical procedure. The former is used to retrieve the antenna input impedance at the end of the waveguide port excitation. The semi-analytical procedure consists in a transmission-line equivalent circuit that models two waveguide discontinuities (namely two capacitive irises) within the waveguide section, whose position and geometric features are finely tuned to obtain a satisfactory impedance matching around the working frequency. The proposed method is shown to be effective in diverse and attractive application-oriented contexts, from the impedance matching of a Fabry–Perot cavity antenna to that of a wireless near-field link between two aperture-fed focusing devices. A remarkable agreement between full-wave simulations and numerical results is found in all cases. Thanks to its versatility, simplicity, and a rather low demand of computational resources, the proposed approach may become an essential tool for the effective design of waveguide-fed antennas.

Tuning of magnetosplamon coupling between graphene scatterers for the optimal design of adjustable metasurfaces

The resonance characteristics of magnetically-biased graphene micro-scatterers are thoroughly investigated in the present work using both eigenvalue and full-wave solvers. Initially, the graphene surface conductivity is presented in a tensor form due to the application of a magnetostatic bias field, which is perpendicular to the material’s surface. Then, the simple case of a graphene disk scatterer is examined, and a properly modified eigenvalue formulation is utilized to extract the plasmonic fundamental frequencies. The validity of the modal analysis is verified via a full-wave analysis that involves a plane-wave propagation and the extraction of the subsequent absorption cross-section utilizing the Finite-Difference Time-Domain method. Additionally, the dependence of a single disk scatterer resonances with the magnetostatic bias is evaluated, highlighting that as the bias field is increased, every edge mode degenerates into two sub-modes with an augmented difference between the resonant frequencies. Finally, the plasmonic coupling between adjacent scatterers is studied considering a periodic arrangement, similar to a metasurface, indicating the additional coupling modes as well as the adjustability of the properties with multiple degrees of freedom.

Using the CLEAN Method in Three-Dimensional Polarimetric ISAR Imaging Based on Volumetric Scattering Points

We developed a new technique for generating three-dimensional monostatic inverse synthetic aperture radar (ISAR) images using various types of polarimetric information on targets. To remove clutter around a target, we adopted the CLEAN method, in which only the main signals were reconstructed using an iterative algorithm. We conducted a simulation as follows: electric field data that were subjected to polarimetric scattering were obtained for the target using a full-wave electromagnetic analysis simulator. The linear polarization data of a 2 × 2 matrix were compressed into the linear to circular polarization data of a 2 × 1 matrix using the Jones vector based on circular polarization. On the grounds of the post-processed data, inverse Fourier transform was carried out to map scattering points to the spatial domain, after which the CLEAN method was used to retain only the primary scattering points.

Matching method of flat layered-uniform lenses

A novel matching method of flat layered-uniform lens antennas is suggested, which assumes introducing the matching layers on both surfaces of the lens. The evaluations of the layers parameters are obtained on the base of simultaneous satisfaction of the focusing condition and the matching condition. The proposed method provides matching of flat layered-uniform lenses in which the required radial dependence of effective dielectric constant is achieved due to the perforation of through holes in dielectric plate following to the certain law. The matching layers may be implemented by means of drilling on the certain deep the holes of larger diameter on the existing holes in the dielectric plate. The full wave analysis of matched and unmatched flat lenses undertaken by means of finite integration method confirms the reduction of power losses caused media mismatching. In the case of flat lens with the diameter and the focus distance equal to 5λ and the thickness of dielectric plate equal to λ the improvement of the lens matching provides increasing of gain by 2 dB within frequency band 13%. The side lobe level including back lobes is reduced by 10…20 dB.

Vortex circular airy beams through leaky-wave antennas

A novel method to design leaky-wave antennas radiating vortex cylindrical Airy beams at microwave frequencies is here presented. Two different approaches are adopted to produce waves with a nonzero orbital angular momentum (OAM): one based on a bull’s eye design excited by a uniform circular array of vertical coaxial probes with proper azimuthal phase delay, and one based on a single coaxial feeder exciting a multi-spiral radiator. Both of them take advantage of backward radial propagation of cylindrical leaky waves promoting circular Airy beams with vortex patterns. The OAM state can be changed by either varying the probe phasing or the number of spiral units. A reference profile is designed under transverse-electric and transverse-magnetic excitation independently. Numerical full-wave analysis are performed using different angular states to validate the antenna design, as well to highlight the different advantages of the two alternative design approaches.

Multi-Band Antenna Design by Reshaping Surface Currents of Higher Order Mode Using CMA Method

A multi-band antenna design by surface current reshaping of higher-order modes is presented. This method utilizes characteristic mode analysis to modify the conventional circular patch antenna in accordance with the surface current distribution of higher-order modes at the L5, S, and L1 bands using CMA. The antenna is evaluated up to four modes inducing fundamental mode. The S and L1 bands are obtained by exciting reshaped higher-order modes, while the L5 lower band is obtained by exciting the fundamental mode using full-wave analysis with 50 Ω coaxial feed. The measurement results are very similar to simulated antenna results. The measured operating frequencies of the proposed antenna are 1177.00 MHz (L5-band), 1575.00 (L1-band) MHz, and 2497.50 (S-band) MHz with associated impedance bandwidth (S11 ≤ −10 dB) are 25.30 MHz (1164.40–1189.70 MHz), 65.30 MHz (1535.50–1600.80 MHz), and 48.60 MHz (2464.10–2512.70 MHz) having desired gain with hemispherical radiation characteristics. These bands are used in Global Positioning Services (GPS) and in Indian Regional Navigation Satellite System (IRNSS) applications.

Synthesis of Polarization-Independent Perfect Anomalous Reflectors via Modulated Metasurfaces and an Analytical Design Model

A systematic approach to the synthesis of polarization-independent metasurfaces for anomalous reflection is presented. A fast analytical procedure is laid out to analyze the electromagnetic (EM) behavior of an impedance-modulated metasurface for arbitrary angles of incidence and reflection, subsequently serving as a means to provide the necessary impedance profile for reflection toward a specific direction, while capturing all propagation mechanisms, including surface waves (SWs) and nonlocal effects. We apply this procedure to design a metasurface for reflecting a normal incident wave to a different reflection angle, where the synthesized impedance is approximated by a discrete design, based on orthogonal metallic patches. This is done to provide control of both cases of incident wave polarization, while the unit cell analysis and extraction of equivalent impedance is easily performed by a full-wave computational eigenmode analysis of the unit cell. The unit cell design is performed by a simple fine-tuning process with minimal geometric modifications, and the actual discrete metasurface design is proven to agree well with the continuous model. The validity of the synthesis approach is perfectly demonstrated by the fabrication and experimental verification of a model design.