Previously Featured Articles

In this work, the efficiency-bandwidth tradeoff inherent to linear, time-invariant (LTI), electrically small antennas is overcome through parametric space-time variation. This enables performance improvements in applications where antenna size, bandwidth, or power are significant limitations.

Exact hybridization of FEM and PO/MoM is accomplished with Spherical Ports. Structures encompassing a large metallic part close to a general, medium-sized body can be analyzed (e.g., lower-frequency Earth-Observation satellites). Intermediate results are stored and reused. This allows analytical rotations/translations, offering unprecedented efficiency and versatility along lifecycles of real projects.

The spatial constraints in a smartphone prevents its antenna from achieving wideband high-gain circularly polarized radiation. A novel antenna booster architecture is proposed to enhance smartphones’ satellite communication. The booster significantly increases a phone’s circularly polarized gain by 6 dB and its overlapping bandwidth to 18.7%.

Multibeam networks are essential for millimeter-wave communications, but current designs are efficient only for orthogonal beams, limiting flexibility. In many cases, however, non-orthogonal beams are required. Non-orthogonal multibeam network designs, though, face poor power efficiency and limited beam flexibility. This work introduces a new class of multibeam networks capable of exciting any set of non-orthogonal beams with optimal power efficiency.

Reconfigurable electromagnetic devices have attracted growing attention in emerging 6G wireless communication systems for their low-cost wave-shaping capability. This paper presents a novel dual-port antenna with highly reconfigurable patterns and independent dual-beam 2D scanning capability. It shows potential for 6G wireless systems, where compact beamforming antennas, such as movable or fluid antenna systems, are becoming increasingly important.

Novel 2-D materials for emerging applications are fragile and their electromagnetic characterization requires nondestructive techniques. In this work, a novel paradigm is proposed for characterizing the sheet resistance of thin conducting films through an accurate, contactless technique based on terahertz time-domain spectroscopy.

Low-cost antenna reconfigurability at high-frequency bands above 100 GHz is still an unresolved challenge. Liquid Crystal (LC) materials, which are broadly used in photonic industries, can become part of the solution when used as a substrate in planar devices such as reconfigurable intelligent surfaces or reflectarray antennas. This research introduces a LC-based reflectarray antenna capable of independently steering the beam of two orthogonal linear polarizations, which has been designed, manufactured and measured at UPM.

This research presents a parallel-plate lens implemented in multilayer PCB technology offering multiple beams over a large angular sector of ±60° at K-band. The proposed solution tackles several key challenges of modern Satcom antenna applications, including wide scanning range, high integration requirements and low losses.

This research demonstrates a simple design approach to achieve practical superdirective antenna arrays. By overcoming traditional challenges such as impedance matching to 50 ohms, high radiation efficiency, and high directivity, it establishes a pathway for achieving super realized gain, paving the way for advancements in wireless technologies like 5G, IoT, and beyond.

Metamaterials, integrated circuits layouts, and many other devices are strongly multiscale. Their electromagnetic analysis is notoriously challenging. We propose MultiAIM, a very efficient method for the electromagnetic analysis of multiscale structures. We demonstrate CPU time savings of up to 16X for the analysis of several structures, including a metagrating antenna and the layout of a real integrated circuit in 3D integration.

The proposed formulation addresses several numerical issues of time-domain boundary integral equations in electromagnetic scattering, including resonant and direct-current instabilities, dense-mesh and large-time step breakdowns, and the loss of solution accuracy at low frequencies. The novel formulation can also be applied to different scatterer geometries and different frequency ranges.

This research advances adaptive mesh refinement in electromagnetic simulation. By introducing a new equation for electromagnetic solving and error estimation, it improves the reliability of both the solution and the adaptive refinement process. Applying mesh refinement on curvilinear nonconformal mesh enhances geometric modeling, leading to simulation results that more accurately reflect real-world outcomes.

An antenna array with high detection capability is proposed for 3-D head imaging systems. The improvement in the array's detection capability is achieved by enhancing the antenna element’s frequency-domain performance and selecting an effective array layout based on the investigation results of how different layouts impact detection performance.

A metacavity-based dual-polarized frequency-diverse metaimager is presented, offering a complexity-reduced, energy-efficient, and cost-effective hardware solution for microwave computational polarimetric imaging applications. The proposed design is capable of retrieving all polarimetric information, facilitating an improved imaging result regardless of the target geometrical features.

For frequency-selective rasorber (FSR) designs, the half-wavelength short-circuit effect constitutes a crucial obstacle in limiting the absorption bandwidth extension, especially when the absorption band is expected to cover low frequencies. An ultra-wideband and dual-polarized FSR with a wide transmission band is presented. By introducing another lossy layer, the absorption band as well as the continuous low-reflection band are enhanced significantly.

There is an urgent requirement in mmW antenna arrays for a low-loss feeding network. This paper proposes a compact feeding network based on two different epsilon-near-zero (ENZ) modes to excite a 2-D scalable mmW slot antenna array, showing an aperture efficiency of 92.1% and a total efficiency of 95.4%.

The research deals with inverse scattering problems, which are at the heart of microwave imaging applications. It introduces a new method for support reconstruction based on a smart reformulation of the scattering equations and is able to significantly alleviate the non-linearity and improve the accuracy with respect to popular qualitative methods.

The radiated-field pattern from a series of waveguide components may be significantly distorted by the higher-order modes in the waveguide. To mitigate such effects, the higher-order mode quantification is essential. This study proposes a method to quantify the higher-order modes from the measurable radiated field with the aid of simulation.

The inherent electromagnetic properties of a sandwich building material significantly affect indoor wireless performance and, thus, need to be considered during building design. Results show that channel capacity can be substantially improved by jointly optimizing the relative permittivity and thickness of all layers of a sandwich-building material.

A 3D corrugated ground structure is proposed as a miniaturization technique suitable for microstrip antennas with a full ground. Unlike existing methods, it neither requires changing the radiator shape nor utilizing shorting vias. Importantly, it avoids a significant reduction in the operational bandwidth while decreasing the cross-polarization level.

The proposed research advances the Ultraweak Variational Formulation (UWVF) method for modeling electromagnetic waves. By enhancing its capabilities, such as integrating curved elements and addressing complex material interfaces, high-frequency wave propagation utility, which is essential for diverse industrial applications, is improved. The implemented simulations, including X-band frequency scattering from aircraft, demonstrate practical significance.

A body-matched dual-polarized cavity-backed antenna with enhanced wave penetration is proposed for electromagnetic torso imaging. Tested with a human torso phantom and confocal imaging algorithm, it stands as a promising solution for imaging deep targets with various shapes and orientations within heterogeneous and lossy mediums, such as the human torso.

Smart Electromagnetic Skins (SES) provide a cost-effective solution for blind zones at mm-wave frequencies for 5G networks and future 5G-Advanced and 6G. This effect is crucial indoors, where users are in the near-field region. The present work experimentally demonstrates a near-field design-based SES for effective coverage considering near-field end-users.

Under inhomogeneous background, aperiodic Frequency-selective surfaces (FSSs) have shown great potential in EM wave controlling. Meanwhile, the design becomes more challenging. An ANN- and adjoint gradient-based method with inhomogeneous Green’s function is introduced to accelerate both forward mapping and inverse design of multifunctional FSS with high degree of freedom.

Bandwidth enhancement through impedance matching has been a constant pursuit for antennas. This paper proposes an active impedance matching circuit with an over-hundred-octave bandwidth based on a single field effect transistor (FET) biased in its ohmic region. With it, an active antenna is realized, covering a 10-1800 MHz bandwidth.

The presented strategy addresses crucial challenges in low-frequency electromagnetic simulation by mitigating the high number of iterations required by iterative solvers and restoring solution accuracy. The proposed approach, leveraging quasi-Helmholtz projectors and high-order basis functions, enables remarkably precise simulations.

A dual-band dual-mode wearable antenna with a hybrid substrate using PDMS and PF4-foam is presented, which allows for enhanced radiation performance while maintaining mechanical flexibility. This technique extracts the desirable mechanical properties from both substrate materials and combines them to achieve improved radiation efficiency according to electromagnetic power distribution.

Future array antennas will include a huge number of densely packed elements with strong edge effects and mutual coupling occurring. The developed method allows for full-wave simulation of array antennas with thousands of elements without resorting to approximations, taking only minutes to complete on a standard laptop.

Inverse imaging problems have non-unique solutions, and both optimization and machine-learning-based solutions often lack quantifiable measures of confidence in their output. Utilizing a machine learning inverse imaging model that provides more than one form of prediction uncertainty can increase the user’s confidence in the output.

This work introduces a hierarchical impedance matching approach, which intuitively unveils the relationship between absorption performance and the characteristic of surface, promising enhanced angular stability for ultra-wideband dual-polarized absorbers. The absorber covers S to Ku bands and has the potential to be applied in the field of electromagnetic protection.

A novel design to fold corporate feed networks is introduced. A minimum of 65% compression to the system is achieved. This mechanism is verified through the fabrication of a single SatCom terminal covering the full band from 17 to 31 GHz and demonstrating a minimum gain of 31.8 dBi.

Focal plane arrays (FPAs) are a compelling solution for imaging at (sub)-millimeter wavelengths to rapidly generate wide field-of-view images. In this article, the capability of shaped quartz lens antennas in significantly enhancing the field-of-view of imaging systems compared to the state-of-the-art horn-based FPAs is investigated and experimentally validated.

A ray-tracing and physical-optics model for planar Mikaelian lens antennas implemented by parallel plate waveguides is proposed. Using the field equivalence principle, the total electric far field of the lens antenna can be computed, which is further employed to calculate the antenna directivity, gain, and dielectric efficiency.

Wide-angle beam-scanning phased arrays are widely demanded for mm-wave communications. However, most of the reported DRA elements suffer from a limited beamwidth or a complex structure, which degrades the beam-scanning performance. In this paper, a very simple widebeam mm-wave DRA is investigated, along with its wide-angle beam-scanning phased arrays.

A bio-symbiotic planar inverted-F antenna is proposed for wearable devices. It is 3D-printed in an engineered meander-shaped structure to be ergonomic and breathable. It is also designed for stable on-body radiation performance during daily activities. These two characteristics make this antenna unique for body-centric wireless power transfer and bio-sensing applications.

The impact on the radiation pattern due to the incorrect deployment of petal reflector antennas is addressed through an innovative method based on Interval Analysis. The proposed approach allows an efficient and reliable computation of the pattern bounds encompassing every possible Monte Carlo simulation.

A novel sub-terahertz fully metallic waveguide-based multibeam antenna is achieved based on the sliding aperture theory and self-compensating waveguide phase shifters. A cost-effective prototype has been realized and experimentally verified, providing a successful example at the band from 410 to 480 GHz.

This work proposes a near-field measurement technique that allows the radiation pattern validation of antennas with integrated RF sources in minimum time (~1 min). The proposed method is suited for the measurement of digital phased arrays and 5G devices where there is no access to a reference channel.

An approach to design a multi-beam Luneburg lens antenna for correlation-based amplitude-only direction-finding systems is presented. The proposed framework expands on the existing literature by prescribing not only the number of detectors and lens radius to meet specific performance requirements but also generalized feed parameters that fit an assortment of lens antenna excitations.

Local mesh refinement is useful to improve simulation performance for multiscale structures. A three-dimensional symmetric FDTD subgridding method with arbitrary grid ratios is proposed for modeling multiscale structures. It is theoretically stable, accurate, highly efficient and flexible due to carefully designed coupling matrices between coarse and subgridding meshes.

A Cycle-Generative Adversarial Network (Cycle-GAN) is used to address the challenge of calibrating Microwave Imaging (MWI) systems without requiring known targets. By treating synthetic and uncalibrated experimental data as two unpaired sets of images, Cycle-GAN calibration facilitates successful quantitative imaging in a 2D system.

The endfire bandwidth of the traditional periodic leaky-wave antenna is usually limited by the Hasen-woodary condition. This severely limits the application scenarios of the leaky-wave antenna in wideband wireless systems. In the present work, the higher-order modes of periodic structure are proposed to be utilized for endfire gain enhancement of the “invisible region”, effectively releasing the limitation of the Hasen-woodary condition.

At present, calibration of large-scale phased array antennas in the near-field setup typically requires a scanner with a scanning aperture larger than the aperture of the array under test (AUT). The proposed calibration method can reduce the size of the scanning aperture to half of the AUT aperture by using amplitude/phase extrapolation algorithm. With the proposed algorithm, future large-scale phased arrays can be calibrated in low-cost and easy-to-implement debugging facilities.

A unified simulation framework is introduced for the dispersive ADE-FLOD-FDTD method based on the multiterm modified Lorentz model. This novel framework enables the expeditious capacity for effectuating rapid simulation of electromagnetic wave propagation in typical dispersive media, thus serving as a critically indispensable numerical simulation tool for time-domain numerical modeling of intricate dispersive media.

A novel approach for designing dual-polarized, shared-aperture, two-dimensional multibeam leaky-wave antenna (LWA) is introduced. Combining the frequency-controlled beam-scanning characteristic of LWA and the quad-beam radiation achieved by four parabolic-reflector-based beamforming networks, the wide-angle beam-scanning capability is realized through one input port, which makes the presented antenna promising for low-cost millimeter-wave applications.

The use of the Linear Sampling Method (LSM) is investigated for determining the shape of a scatterer from multi-frequency experimental data. A deep understanding of the quality of multi-frequency LSM reconstruction from realistic antenna transmitting systems is of key importance for applications in nondestructive testing.

Conventional near-field-to-far-field transformation algorithms with first-order probe correction severely limit the possible antenna combinations that can be deployed in spherical near-field test ranges. This work introduces new iterative three-antenna characterization techniques, based on higher-order probe correction, enabling the full characterization of up to three potentially complex antennas.

An electronically reconfigurable reflectarray that can operate in dual linear and dual circular polarization modes with simultaneous beam scanning capability is introduced. The highlight of this work is that only 1-bit phase resolution is used to achieve quad-polarization conversion phase shift through array arrangement, which greatly reduces the system complexity.

This work presents unique measurements of sky-noise temperature and atmospheric attenuation up to W-band and in all-weather conditions available from the only two sites in the world equipped with a Sun-tracking microwave radiometer. The large and robust database allowed the design of an innovative atmospheric model for non-geostationary satellite links.

Inverse source formulations are key elements of antenna design procedures. This work’s contributions are twofold: we propose a Love inverse source formulation requiring half-the-size matrices, clearly leading to substantial computational savings; we also propose the first stabilization of the Steklov-Poincare operator using projectors. This paves the way to wide band applications of otherwise only high frequency schemes, something very relevant for biomedical imaging such as neuroimaging.

A novel 7m x 1.5m parabolic cylinder foldable/deployable mesh reflector antenna with tensegrity configuration and unprecedentedly low stow-volume and mass is designed, prototyped, and measured for the global mapping of Earth's Surface Deformation and Change (SDC) using space-based small satellite remote-sensing synthetic aperture radar (SAR) in Low-Earth orbit.

This is the first large-scale indoor assessment of the Smart ElectroMagnetic Environment (SEME) paradigm using static passive EM skins (SP-EMSs) to enhance 5GHz Wi-Fi coverage mimicking a realistic user-experience. Proofs of the effectiveness as well as economic benefits of the SEME deployment with respect to the densification of active radiating sources are provided.

Modulated metasurfaces are able to realize a low-profile antenna with multiple beams. The present work proposes a new method to reduce mutual interference of different impedance modulations corresponding to different beams. As a result, it is the first time that seven beams are radiated by a single modulated metasurface using seven ports.

A dual-band antenna for metal-bezel smartwatches, achieving circular polarization in GPS band via a capacitor, is introduced. A simple metal plane is proposed to significantly mitigate the negative effect from human wrist and enhance antenna efficiency and stability, thus making the presented antenna promising for practical applications.

A novel solution for designing planar endfire antennas with wide bandwidth and compact physical apertures is introduced. By leveraging trapped waves supported by metasurfaces, we overcome existing design challenges. This work contributes to advancing antenna technology, enabling enhanced performance in wireless communication systems and paving the way for innovative applications.

Parallel plate slot array antenna suffers from low aperture efficiency due to the intrinsic multi-mode feature of the oversized waveguide. In this study, a novel feeding network with centered-longitudinal slots is proposed for reducing the field ripples in the parallel plates, which significantly improves the aperture efficiency.

Exploring a dual-band high-gain antenna with a small footprint and lightweight is essential and always a primary choice in many potential applications, particularly satellite-based communication systems for simultaneous data streams in full-duplex. The proposed work is the first realization of a near-field phase correction metascreen operating in the Ku bands. A fully metallic slot-based architecture with high structural integrity is devised, significantly reducing cost, weight, and fabrication complexity. The elimination of dielectrics also enhances the capability to avoid typical issues encountered by dielectric materials in space and high-power applications, such as radiation damage, degassing, carbonization, and dielectric breakdown.

Real-time information interaction among vehicles and other devices is essential for autonomous driving. To overcome disadvantages of installing several separated antennas on a common platform, a compact multifunctional antenna with concurrent broadside RHCP for V2S communication and bidirectional end-fire LP radiation for V2X communication is presented.

A piezoelectric crystal is employed together with appropriate metallic boundaries to build efficient EM radiators by utilizing piezoelectric effect in antenna engineering. The radiation efficiency of a demonstrated prototype exceeds the upper limit of metallic antennas.

Few designs, to date, can realize the integration of MW PIFA antenna and broadside MMW beam-steering array. The proposed antenna fills this gap by using a uniform substrate, achieving a high integration level with a small clearance of only 7mm. In this design, the MMW SIDRA, which is a 1×4 connected DRA array, is developed in the clearance area of the PIFA.

Inherent loss in practical materials hinders achieving accurate radiation patterns in printed metasurface antennas. The paper proposes a modulated metasurface leaky-wave antenna design technique that accurately accounts for dielectric and conductor losses. Based on penetrable aperture field synthesis, the design is capable of realizing various radiation patterns accurately.

A novel 5G air-to-ground (ATG) array for aviation applications is realized through reconfigurable technique. The reduced cross-sectional area, full azimuth coverage and low complexity of the array provides significant advantages over conventional solutions. The array design is beneficial in promoting the future 5G applications.

Reducing the number of antennas in a radar front-end will result in reducing the number of RF channels, thereby reducing cost and power consumption. We overcome the difficulty of degrading the performance of the radar due to the reduced number of antennas and propose a highly efficient algorithm to guide the aperiodic arrangement.

Specifications for satellite communication require an ultra-wideband antenna with a high gain and high efficiency. In this study, an ultra-wideband cavity-backed antenna that covers uplink and downlink bands for Ku-band direct broadcasting devices (DBS) is proposed, which results in weight reduction, especially for unmanned aerial vehicles (UAV).

Enhanced circularly-polarized radiation, under the condition that the structural compatibility with the existing protective dome shell embodied by the truncated icosahedron is taken into account, is achieved through a hemispherical metasurface. The dome, capable of radiation conversion, can facilitate the link enhancement while the system’s compactness and skin curvature are well retained.

This paper presents lower Q-factor bounds for microstrip patch antennas, orders of magnitude tighter than the Chu limit. These bounds provide achievable bandwidth benchmarks and a guide to assess required design parameters. An easy-to-compute approximation of these bounds is also proposed.

A typical leaky-wave antenna (LWA) and its natural frequency-scanned beam are inevitably subject to the narrowband characteristic towards a certain spatial angle. This would impede LWAs from being deployed for wideband systems such as modern radars needing good range resolutions or communications requiring high transmission rates. Our research is structured under such background, providing the feasibility of augmenting the application versatilities of LWAs and facilitating them to be potentially exploited for wideband wireless systems.