Search Results (754)

Extremely low-frequency (ELF, 3–30 Hz) signals are effective for cross-medium transmission, yet conventional implementations are hindered by their large size and low efficiency. To address these limitations, a compact electromechanical–magnetic antenna (EMA) was developed and experimentally validated for ELF magnetic communication. The basic unit of the antenna, a single-EMA, consists of a stacked magnetostrictive composite beam, piezoelectric ceramic plates, and tip-mounted permanent magnets. The total envelope volume of a single EMA is only 3.3 cm³ with a maximum length of 12 cm, representing a substantial reduction compared with conventional ELF antennas. Building on this compact architecture, two EMAs were operated in parallel to form a parallel-EMA system, which significantly enhanced magnetic radiation through constructive magnetic coupling. Moreover, the optimal separation distance between the two EMAs was identified, ensuring efficient cooperative radiation. When driven at 50.2 mW, the parallel-EMA configuration generated a magnetic flux density of 114 pT at a transmission distance of 20 m in seawater. This performance demonstrates nearly a twofold improvement over a single-EMA unit, validating the scalability of parallel operation for stronger magnetic radiation. The compact form factor of the single EMA combined with the enhanced radiation performance of the parallel-EMA system enables portable ELF magnetic communication across diverse cross-medium scenarios, including air-to-sea and underground-to-air links. Full article

In this paper, a pattern synthesis method of uniform linear and concentric elliptical antenna arrays using the Kepler optimization algorithm (KOA) is proposed. The KOA, which utilizes Kepler’s laws to predict the position and velocity of planets at arbitrary times, is first applied to deal with the optimization problems of linear and elliptical antenna arrays. Radiation patterns with high gain and low sidelobe levels (SLLs) are synthesized by optimizing the critical parameters (amplitude, phase, and rotation) of the linear arrays. Moreover, a concentric elliptical array is designed to demonstrate the capability of the KOA framework to solve complex problems and achieve the desired performance. In order to accurately consider mutual coupling between the elements, the full-wave method of moments (MoM) is used to calculate the radiation characteristics of the arrays in the optimization method. The effectiveness of the proposed method is proved by four typical examples. The results show that, compared with the butterfly optimization algorithm (BOA), Harris hawks optimization (HHO), and crayfish optimization algorithm (COA), the proposed method possesses high gain and SLL suppression capabilities, which makes it suitable for various array types. Full article

A compact fork-shaped four-element multiple-input multiple-output (MIMO) antenna system with wide bandwidth for 5G millimeter-wave (mmWave) applications is presented. The antenna elements are arranged orthogonally to achieve a compact footprint of $20\times 26{\mathrm{mm}}^2$. To enhance the gain, a frequency selective surface (FSS) is placed above the MIMO system, providing an average gain improvement of 1.5 dB across the entire operating band and achieving a peak gain of 7.5 dB at 41 GHz. The proposed design operates in the Ka-band (22–46 GHz), making it well suited for 5G communications. The antenna exhibits an isolation greater than 20 dB and radiation efficiency exceeding 80% across the band. Moreover, key MIMO performance metrics, including diversity gain (DG ≈ 10) and envelope correlation coefficient (ECC < 0.05), meet the required standards. A prototype of the proposed system was fabricated and measured, with the experimental results showing good agreement with simulations. Full article

This paper presents a multi-problem surrogate-assisted evolutionary multi-objective optimization approach for antenna design. By transforming the traditional antenna design optimization problem into expensive multi-objective optimization problems, this method employs a multi-problem surrogate (MPS) model to stack multiple antenna design problems. The MPS model is a knowledge-transfer framework that stacks multiple surrogate models (e.g., Gaussian Processes) trained on related antenna design problems (e.g., Yagi–Uda antennas with varying director configurations) to accelerate optimization. The parameters of Yagi–Uda antenna including radiation patterns and beamwidth—across various director configurations are considered as decision variables. The several surrogates are constructed based on the number of directors of Yagi–Uda antenna. The MPS algorithm identifies promising candidate solutions using an expected improvement strategy and refines them through true function evaluations, effectively balancing exploration with computational cost. Compared to benchmark algorithms assessed by hypervolume, our approach demonstrated superior average performance while requiring fewer function evaluations. Full article

Deeply implanted biomedical devices like leadless pacemakers require an antenna with minimal volume and high radiation efficiency to ensure reliable in-body communication and long operational time within the human body. This paper introduces a novel implantable antenna designed to significantly reduce the spatial requirements within an implantable capsule while maintaining high radiation efficiency in lossy media like heart tissue. The design principles of the proposed antenna are outlined, followed by antenna parameters and an equivalent circuit study that demonstrates how to fine-tune the antenna’s resonant frequency. The radiation characteristics of the antenna are thoroughly investigated, revealing a radiation efficiency of up to 28% at the Medical Implant Communication System (MICS) band and 56% at the 2.4 GHz ISM band. The transmission efficiency between two deeply implanted antennas within heart tissue has been improved by more than 15 dB compared to the current state of the art. The radiation and transmission performance of the proposed antennas has been validated through comprehensive simulations using anatomical human body models, phantom measurements, and in vivo animal experiments, confirming their superior radiation performance. Full article

This paper presents the design and experimental evaluation of a compact microstrip patch antenna and a 4 × 4 phased antenna array system tailored for Wi-Fi 6E applications, U-NII-5 band. A single inset-fed microstrip patch antenna was first optimized through full-wave simulations, achieving a resonant frequency of 5.96 GHz with a measured return loss of −17.5 dB and stable broadside radiation. Building on this element, a corporate-fed 4 × 4 array was implemented on an FR4 substrate, incorporating stepped-impedance transmission lines and λ/4 transformers to ensure equal power division and impedance matching across all ports. A 4-bit digital phase shifter, controlled by an ATmega328p microcontroller, was integrated to enable electronic beam steering. Simulated results demonstrated accurate beam control within ±28°, with directional gains above 13 dBi and minimal degradation compared to the broadside case. Over-the-air measurements validated these findings, showing main lobe steering at 0°, ±15°, +33° and −30° with peak gains between 7.8 and 11.5 dBi. The proposed design demonstrates a cost-effective and practical solution for Wi-Fi 6E phased array antennas, offering enhanced beamforming, improved spatial coverage, and reliable performance in next-generation wireless networks. Full article

Direct radiating arrays (DRAs) present favorable solutions for high-throughput flexible coverage in geostationary (GEO) broadband satellite missions. The ultimate constraint in these architectures is the high number of digitally controlled antenna ports, which renders fully digital architectures impractical for the immediate future. Instead, hybrid analog–digital DRAs are being considered as a promising trade-off in terms of performance/flexibility and digital processing demands. These architectures commonly involve subarrays with analog beamforming, which form broad (regional) beams, which are then digitally beamformed at a second level to produce a multitude of narrow beams used for broadband connectivity. Due to the large size of the subarrays, these architectures are subject to undesired grating lobes that can lead to interference and reduce the gain of the main beam, thereby compromising overall performance. Partial mitigation of the grating lobes is attainable by subarray overlapping. This paper presents a comparative assessment of three different hybrid analog–digital DRA architectures in terms of the coverage characteristics and discusses their practical implementation. It is demonstrated that improved performance can be achieved by subarray overlapping with some additional analog hardware complexity but otherwise maintaining the number of digitally controlled antenna ports. Full article

This paper presents the design and development of a reconfigurable circular array antenna capable of producing ten distinct radiation beams, intended for wireless systems in the sub-6 GHz frequency band. The antenna structure is based on four pentagon-shaped radiating elements arranged symmetrically around a central circular patch, which is excited through a coaxial feed. These radiating elements are linked by four circular segments, ensuring mutual coupling for effective operation. A systematic dimensional analysis has been conducted to optimize electromagnetic performance, resulting in a compact and efficient architecture. The beam reconfiguration is achieved through the control of four PIN diodes, which allow the main radiation beam to switch among ten different orientations in the azimuth plane. Specifically, the antenna supports eight directional states, oriented at 45° intervals, and two additional bidirectional states covering opposite directions. A prototype has been fabricated and experimentally validated, confirming the steering capability of ±40° in both the XZ and YZ planes. Performance evaluation shows a maximum gain of 9.29 dBi and efficiency levels ranging from 91% to 97%. Bandwidth varies across states, with 9.72% for S1–S7, 7.45% for S2–S8, and 4.61% for S9–S10. Overall, the proposed design demonstrates optimized bandwidth, gain, efficiency, and complete azimuthal coverage. Full article

This paper presents the design and performance evaluation of a compact four-element coplanar waveguide (CPW)-fed antenna array operating in the 3.3–3.6 GHz frequency band. The proposed antenna is tailored for sub-6 GHz 5G New Radio (NR) applications, specifically aligning with the n77/n78 bands widely adopted for mid-band 5G deployment. The CPW feeding technique enables low-profile integration and ease of fabrication, while the multi-element configuration supports enhanced gain and spatial diversity. Both simulated and measured results demonstrate good impedance matching (|S₁₁| < −10 dB), stable radiation patterns, and inter-element isolation suitable for MIMO operation. The design offers a promising solution for compact 5G antenna systems and can be extended to future wireless communication platforms requiring high efficiency and compact form factors. Full article

This study presents a compact, wideband fractal antenna fabricated using silver nanoparticles (AgNPs) and screen-printing technology. The antenna consists of a decagonal monopole patch and a mesh ground plane, both printed on a transparent polyethylene terephthalate (PET) substrate. The proposed antenna has a compact size of 18 × 16 × 0.55 mm³, achieved by stacking two PET layers joined using double-sided tape. The antenna covers both C- and X-bands, with measured optical transmittance of 68.1% and radiation efficiency of 72%. The simulated −10 dB bandwidth (without bending) spans 4–10.8 GHz and 11.2–12.5 GHz, while the measured −10 dB bandwidth is 3.8–11.2 GHz without bending, 3–11.4 GHz at 30° bending, and 3–11.2 GHz at 45° bending, confirming that there was stable performance under flexure. The conductive patterns were formed using silver nanoparticle paste with a sheet resistance of 0.2 Ω/sq, followed by annealing in a vacuum oven at 140 °C for 20 min. The proposed antenna was tested under 30° and 45° bending, and the measured S₁₁ remained stable, confirming flexibility. The use of a flexible, optically transparent PET substrate enables installation on curved or see-through surfaces. Combining compact size, wideband performance, cost-effective fabrication, and optical transparency, the antenna demonstrates strong potential for application in X-band radar, C-band satellite communications, and S-band Wi-Fi. Full article

Novel K band wearable sensors and antennas for Telemonitoring, Telehealth and Telemedicine Systems, Internet of Things (IoT) systems, and communication sensors are discussed in this paper. Only in a limited number of papers are K band sensors presented. One of the major goals in the evaluation of Telehealth and Telemedicine and wireless communication devices is the development of efficient compact low-cost antennas and sensors. The development of wideband efficient antennas is crucial to the evaluation of wideband and multiband efficient Telemonitoring, Telehealth and Telemedicine wearable devices. The advantage of the printed wearable antenna is that the feed and matching network can be etched on the same substrate as the printed radiating antenna. K band slot antennas and arrays are presented in this paper the sensors are compact, lightweight, efficient, and wideband. The antennas’ design parameters, and comparison between computation and measured electrical performance of the antennas, are presented in this paper. Fractal efficient antennas and sensors were evaluated to maximize the electrical characteristics of the communication and medical devices. This paper presents wideband printed antennas in frequencies from 16 GH to 26 GHz for Telemonitoring, Telehealth and Telemedicine Systems. The bandwidth of the K band fractal slot antennas and arrays ranges from 10% to 40%. The electrical characteristics of the new compact antennas in the vicinity of the patient body were measured and simulated by using electromagnetic simulation techniques. The gain of the new K band fractal antennas and slot arrays presented in this paper ranges from 3 dBi to 7.5 dBi with 90% efficiency. Full article

In modern laptops, antenna design for Wi-Fi 7 is constrained by limited space and reduced ground plane size, conditions under which many compact designs exhibit degraded bandwidth or efficiency or require large device grounds. This paper presents a miniaturized tri-band inverted-F antenna (IFA) that supports the 2.4, 5, and 6 GHz Wi-Fi 7 bands within a radiator area of 20 × 5 × 0.8 mm³ and a ground plane of 60 × 40 mm². The proposed design achieves wideband impedance matching and stable radiation efficiency under intentionally reduced grounding conditions, addressing a scenario rarely considered in prior studies where both radiator and ground plane miniaturization must be satisfied. Measurements confirm efficiencies of 74–81% at 2.4 GHz and 64–90% across 5–7 GHz, with performance in the lower band exceeding that of many compact designs and upper-band coverage comparable to structures requiring larger footprints. By demonstrating tri-band operation under simultaneous radiator and ground reduction, this work provides a practical antenna solution for next-generation Wi-Fi 7 laptop integration. Full article

With the rapid growth of unmanned aerial vehicles (UAVs) and IoT users, spectrum resources are becoming increasingly scarce, making cognitive radio (CR) technology a key approach to improving spectrum utilization. However, traditional antennas are difficult to meet the lightweight, compact, and low-drag requirements of small UAVs due to spatial constraints. This paper proposes a tri-mode frequency reconfigurable flexible antenna that can be conformally integrated onto UAV wing arms to enable CR dynamic frequency communication. The antenna uses a polyimide (PI) substrate and has compact dimensions of 31.4 × 58 × 0.05 mm³. A microstrip line-based frequency-selective network is designed, incorporating PIN and varactor diodes to realize three operation modes, dual-band (2.25~3.55 GHz, 5.6~6.75 GHz), single-band (3.35~5.3 GHz), and continuous tuning (4.3~6.1 GHz), covering WLAN, WiMAX, and 5G NR bands. Test results show that the antenna maintains stable performance under conformal conditions, with frequency shifts less than 4%, gain (3.65~4.77 dBi), and radiation efficiency between 67.2% and 82.9%. The tuning ratio reaches 38.8% in the continuous mode. This design offers a new solution for CR communication in compact UAV platforms and shows promising application potential. Full article

Phase-retrieval problems are employed to tackle the challenge of recovering a complex signal from amplitude-only data. In phaseless spherical near-field antenna measurements, the task is to recover the complex coefficients describing the radiation behavior of the antenna under test (AUT) from amplitude near-field measurements. The coefficients refer, for example, to equivalent currents or spherical modes, and from these, the AUT’s far-field characteristic, which is usually of interest, can be obtained. In this article, the concept of a mask-based phase recovery is applied to spherical near-field antenna measurements. First, the theory of the mask approach is described with its mathematical definition. Then, several mask types based on random distributions, $\varphi$-rotations, or probes are introduced and discussed. Finally, the performances of the different masks are evaluated based on simulations with multiple AUTs and with Wirtinger flow as a phase-retrieval algorithm. The simulation results show that the mask approach can improve the reconstruction error depending on the number of masks, oversampling, and the type of mask. Full article

This paper presents the design of a circularly polarized RFID ground mat antenna for UHF-band sports-event applications. Considering a practical sports-event timing system, the ground-based mat antenna with characteristics of a low-backward radiation and circular polarization is proposed. A multilayer square patch antenna using an acrylic dielectric substrate with a wideband branch-line coupler feeding network is employed to improve overall radiation efficiency, which, in turn, provides two excitation port with a phase difference of 90°. Thus, right-hand circular polarization can be obtained. Instead of a conventional FR4–air–FR4 structure, the proposed FR4–acrylic–FR4 composite configuration is adopted to substantially increase the antenna’s mechanical strength and durability against external pressure from runners. The antenna’s performance is attributed to the use of an effective composite dielectric constant and an optimized design of its parameters. Additionally, the patch antenna’s low-backward radiation characteristic helps reduce multipath interference in real-world applications. The measured results are in good agreement with the simulated data, validating the proposed antenna design. In order to further assess the practical performance of the antenna, outdoor measurements are carried out to validate the estimated reading distances derived from controlled anechoic chamber tests. The measured return loss remained below −10 dB across the frequency range of 755–990 MHz, exhibiting a slight discrepancy compared to the simulated bandwidth of 800–1030 MHz. For the characteristic of the circular polarization, the measured axial ratio is below 3 dB within the range of 860–920 MHz. While a more relaxed criterion of an axial ratio below 6 dB is considered, the operating frequency range extends from 560 MHz to 985 MHz, which falls within the frequency band relevant for RFID reader applications. Full article