Search Results (281)

Compact sub-6 GHz and wireless local area network (WLAN) multiple-input multiple-output (MIMO) antennas require broad impedance coverage and low inter-port coupling within limited footprints. This work presents a two-port Koch-fractal U-slot antenna with a defected ground structure (DGS) on RT/duroid 5880. The design evolves from a rectangular monopole through Koch-edge shaping, U-slot loading, and ground-plane defects. The fabricated two-port prototype exhibits a measured −10 dB impedance bandwidth of 3.07–6.02 GHz, covering n78, n79, and WLAN, while the measured inter-port isolation exceeds 18.13 dB. The fabricated single-element prototype provides measured realized gains of 1.92, 2.34, and 2.05 dBi at 3.5, 4.7, and 5.5 GHz, respectively. Measurement-derived MIMO metrics yield an envelope correlation coefficient not exceeding 0.002, diversity gain close to 10 dB, channel capacity loss of 0.07–0.10 bits/s/Hz, mean effective gain near −3.1 dB with zero port imbalance, and acceptable in-phase total active reflection coefficient behavior. WLAN-band quadrature phase-shift keying tests at 5.18, 5.50, and 5.825 GHz produce error vector magnitude values of 5.4–9.1%, with derived bit error rate estimates below 10⁻⁶ under an additive white Gaussian noise assumption. The design provides wide measured bandwidth, good isolation, low correlation, and WLAN-band signal-domain validation in a simple printed structure. Full article

This research paper investigates the impact of inserting a ground slot on the frequency performance of a monopole-type microstrip patch antenna. To examine this, a reference antenna, which is a simple rectangular monopole with the dimensions 2.4 × 2.04 mm², was mounted on a 12 × 12 mm² Rogers RT 5880 substrate with a thickness of 0.254 mm and a dielectric constant of εᵣ = 2.2. It was also fed by a 50 Ω microstrip line. This work compares the effects of four different geometries of rectangular ground slots: rectangular, triangular, half-ring, and half-circle, on the performance of the microstrip patch antenna. The no-slot baseline antenna showed a resonance of 12.55 GHz and a reflection coefficient of −15.9 dB. Adding a ground slot allowed the advent of single or dual-resonant frequencies, which significantly enhanced the appropriateness of the antenna in 5G usage. Notably, the rectangular slot with b₁ = 3 mm achieved a resonance of 22.5 GHz, with a reflection coefficient of −33.7 dB, while b₁ = 1 mm enabled dual-band operation at 11.77 GHz and 38.3 GHz. Triangular slots provided strong single-frequency operation between 26 GHz and 31 GHz, and the half-circle slot with r₃ = 1 mm resonated at 12 GHz with a reflection coefficient of −39.5 dB. Although the half-ring slot had a comparatively lower reflection coefficient, it still showed dual-band potential at 11.1 GHz and 34.14 GHz. The simulation results were validated using HFSS, demonstrating good alignment. The gain of the selected antennas was also investigated, where the highest gain of 4.2 dBi was achieved by the half-ring slot design, and the lowest gain of 3.09 dBi was obtained with the half-circle slot. These findings confirm that ground-slot integration is an effective technique for frequency tuning and performance enhancement in 5G antenna design. Full article

In this paper, a tri-band omnidirectional shark-fin antenna for vehicular communications is proposed, which can cover three operating bands: Ultra High Frequency (UHF, 400–470 MHz), LTE Band 5 (824.2–879.2 MHz), and LTE-1800 (1765–1880 MHz). The antenna integrates a central UHF monopole and a pair of symmetric printed radiating elements within a compact shark-fin radome. The printed elements excite independent resonant modes in each band by using T-shaped and I-shaped radiating branches; broadband matching and balanced excitation are realized through a tapered impedance transformation network; and a dual-band array configuration is adopted to improve gain and stabilize radiation patterns. The monopole and printed elements form a collaborative array in a limited space, achieving structural miniaturization while obtaining good isolation and omnidirectional radiation characteristics. Results show that the peak gain of the antenna is 2.3 dBi in the UHF band and 7.2 dBi in the LTE-1800 band, and the isolation is better than 10 dB. The measured results are consistent with simulations, verifying the feasibility of the proposed design for application in high-performance vehicular communication systems. Full article

This paper addresses the challenge of accurately evaluating the grounding loss of coastal very-low-frequency (VLF) monopole antennas under tidal coverage. An equivalent conductivity calculation method based on a layered lossy transmission line model and Wait’s equivalent admittance of ground screens is proposed to obtain the local equivalent conductivity of the tidally covered area. A sector-ring grounding loss model is then established, incorporating tidal depth, coverage area, and ground screen structure, and the effects of tidal coverage extent, tidal depth, non-uniform radial ground screens, and diurnal tidal dynamics on the grounding loss resistance are analyzed. The proposed analytical model is validated against full-wave FEKO simulations over 20–25 kHz, with an average relative error of 6.67%. Results show that when tidal water covers the sparse outer region of the ground screen, the highly conductive seawater layer provides an additional low-resistance return path, reducing grounding loss. When the tide intrudes further into the high-density inner region, current redistribution among the seawater layer, soil, and metallic ground screen weakens the loss reduction or even causes a non-monotonic increase. This work provides a theoretical basis for the tide-adaptive design of grounding systems for coastal VLF antennas. Full article

This work presents the design of a deployable reconfigurable monopole antenna based on a triangular cylindrical origami structure (TCO). TCO structures are three-dimensional geometries able to modify their structure if subjected to specific solicitations. They are particularly useful for the design of deployable antennas in satellite communication applications. A TCO structure begins from a two-dimensional base composed of an N-faced polygon around which are triangles arranged in a circular pattern to give the structure a cylindrical shape once assembled. The structure is closed with an upper face that can move when stressed. In fact, by applying a force on the upper face, the structure can bend through a combined movement of rotation and translation, expanding or contracting its physical length and consequently the operative frequency. The use of a TCO structure provides a light, cheap, compact, and reconfigurable monopole antenna, particularly suitable for satellite applications. Moreover, by using multiple TCO segments that can be singularly activated, it is possible to control the antenna’s electrical length and consequently obtain a frequency reconfigurable antenna. To demonstrate the effectiveness of such a structure, an antenna prototype based on a TCO is been designed, fabricated, and numerically and experimentally assessed. The obtained results demonstrate the potentialities of such antenna, especially for satellite communication applications. Full article

This paper presents a compact fractal-based super-wideband multiple-input multiple-output (MIMO) antenna for millimeter-wave (mmWave) 5G new radio (NR) and prospective 6G applications. The MIMO system comprises four Koch fractal monopole elements integrated with a modified shared ground plane. By adopting the second Koch iteration, the antenna achieves enhanced impedance bandwidth and stable radiation behavior compared with lower-order iterations. The elements are arranged in a polarization-diversity configuration within a 30 × 30 mm² footprint on a 0.8 mm-thick Rogers RO4835 substrate (ε_r = 3.5, δ = 0.0025). The proposed design provides an impedance bandwidth exceeding 14 GHz over 26.5–41 GHz, covering key bands at 28, 32, 38, and 40 GHz, while maintaining high inter-element isolation (around 30 dB over the operating range). The optimized ground modification enables a fully connected common ground and suppresses mutual coupling without additional decoupling structures. The antenna achieves 4–6 dBi realized gain with radiation efficiency exceeding 95%. MIMO performance metrics, including the envelope correlation coefficient (ECC), mean effective gain (MEG), and diversity gain (DG), confirm excellent diversity characteristics. The antenna is further evaluated under bending, demonstrating stable matching and isolation for conformal and wearable scenarios, and the concept is extendable to a non-planar 12-port configuration within the same footprint. Measured results agree well with simulations, validating the proposed design for wideband mmWave 5G/6G devices. Full article

This paper presents a compact modified monopole antenna tailored for 5G NR on-glass automotive applications operating in the n78 band. The design overcomes 3D radiation pattern limitations inherent in conventional monopole and inverted-F antennas (IFAs). Unlike traditional structures where auxiliary branches serve impedance matching or grounding, this design integrates open- and short-circuited stubs with a coplanar waveguide (CPW) feed to eliminate discrete components. By utilizing a resonant mechanism distinct from IFAs, it enables precise control over the current distribution and phase on the radiator to achieve passive 3D beam shaping without active switches or arrays. This suppresses the inherent elevation null, enhancing upper-hemisphere radiation. A prototype operating from 3.3 to 3.6 GHz was fabricated on a flexible printed circuit (FPC) and verified on a glass substrate. This study focuses strictly on radiation characteristics at the antenna element level; to ensure a focused investigation on dielectric-antenna interactions, large-scale vehicle body scattering and full-scale vehicle integration are excluded from this scope. The results, including S-parameters, gain, total efficiency, and 3D patterns, demonstrate superior elevation coverage and comparable impedance performance under on-glass boundary conditions. The proposed methodology offers a high-feasibility, low-complexity, and cost-effective solution for passive 3D radiation control in on-glass 5G wireless links. Full article

In microwave tomography (MWT), reconstruction accuracy is challenged by modeling error, namely the mismatch between the numerical representation and the actual experiment. Accurate antenna modeling is perceived as an important step toward reducing this error, but the actual benefit of increasing antenna model complexity has not been analyzed in the literature. This work fills this gap by conducting a rigorous numerical analysis of the issue using two popular algorithms for its study: the finite-difference time-domain (FDTD) method for antenna and forward-problem modeling, and the distorted Born iterative method (DBIM) for implementing the iterative inversion algorithm. We consider various FDTD tools of increasing complexity to improve the agreement between the FDTD forward solver and an accurate numerical model implemented in commercial software. After validating these models for different antennas, we perform reconstructions for a stroke-detection scenario. Our results show that in a practical setting, sophisticated antenna modeling in the forward solver does not necessarily improve reconstruction accuracy for monopole-type antennas widely used in MWT. Our model-error analysis confirms that calibration is always necessary in practice and that its impact supersedes efforts to model the antenna more faithfully. Full article

To address the demanding requirements for high gain, wide bandwidth, and stable circularly polarized (CP) radiation in wireless local area network (WLAN) applications, this paper proposes and implements a broadband circularly polarized array antenna primarily targeting the 2.4–2.484 GHz ISM band. The design employs a coplanar waveguide fed broadband CP monopole antenna as the radiating element. A sequential rotation technique is utilized to form a four-element array, and a windmill-shaped defected ground structure is introduced to further extend the bandwidth. The antenna is fabricated on a low-cost FR4 substrate with overall dimensions of 0.98λ₀ × 0.98λ₀ × 0.008λ₀ at 2.4 GHz. Simulation and measurement results show that the array antenna achieves a −10 dB impedance bandwidth of 1.22–2.78 GHz (87.1% relative bandwidth) and a 3-dB axial ratio bandwidth of 1.85–2.66 GHz (35.0% relative bandwidth), ensuring sufficient margin over the target WLAN band. At the center frequency of 2.45 GHz, the antenna exhibits left-hand circular polarization radiation, with a measured peak gain of 8.2 dBic and a cross-polarization discrimination better than 20 dB. To verify its performance advantages in practical systems, the designed antenna was integrated into a ZigBee wireless communication system for data transmission testing. Under controlled conditions, the system employing the proposed antenna achieves a packet loss rate of 3.0% ± 0.4% in a complex multipath environment, significantly outperforming a traditional linear-polarized whip antenna (19.0% ± 1.1%). The results demonstrate that the proposed antenna, featuring wide bandwidth, high gain, and strong anti-interference capability, is a robust solution for WLAN access points and internet of things gateways. Full article

The design, fabrication, and characterization of a highly transparent and flexible monopole antenna optimized for the 3–6 GHz frequency band are presented in this study. In traditional Transparent Conductive Oxide (TCO) designs, there is always a trade-off between RF efficiency and optical transparency. Therefore, an Aerosol Jet^® 5X system was used to directly print a silver nanoparticle mesh onto a 50 μm colorless polyimide (PI) substrate. Using this fabrication method, a durable structure was obtained that exhibits reliable electrical and mechanical performance, achieving 85% optical transmittance in the visible spectrum and a gain of −2.5 dBi. To evaluate the flexibility and compatibility of the antenna, it was bent over a cylindrical surface and integrated with a commercial solar panel in both simulation and experimental environments. The results demonstrate that the impedance matching and radiation characteristics remain stable under bending conditions, with no critical decrease observed in solar energy harvesting. Consequently, this design has strong potential as a solution for energy-autonomous Internet of Things systems, smart windows, and CubeSat applications. Full article

This article presents a meta-surface-based antenna configuration aimed at enhancing the gain performance for millimeter-wave wireless communication systems. The proposed structure consists of a rectangular meta-surface with circular cut-outs placed beneath a rectangular ring to improve the electromagnetic characteristics of the antenna. A rectangular monopole antenna is designed to operate at dual frequency bands around 38 GHz and 43 GHz. To further enhance radiation performance, Artificial Magnetic Conductor (AMC) structures are incorporated beneath the antenna element. The AMC surface improves the radiation efficiency and stabilizes the antenna characteristics by providing in-phase reflection near the operating frequencies. Simulation results demonstrate that the integration of the AMC structure significantly enhances the antenna gain and impedance matching performance. In particular, the incorporation of a $4\times 4$ AMC array increases the antenna gain from approximately 3.4 dB to 6.4 dB while maintaining stable reflection coefficient characteristics. The proposed design demonstrates improved gain performance and compact structure, making it a promising candidate for millimeter-wave wireless communication applications. Full article

This study investigates algorithm-driven placement optimization of two aircraft-mounted VHF monopole antennas to mitigate mutual coupling under realistic installation constraints. A parameterized 3D aircraft model inspired by general-aviation platforms is analyzed using full-wave electromagnetic simulations over the 30–100 MHz band. The optimization problem is formulated to reduce inter-antenna coupling across the operating band while restricting the search space to physically installable regions on the airframe. Two global optimization methods, Genetic Algorithm and Particle Swarm Optimization, are applied and compared under the identical constraints and objective definitions. The results show that both optimizers achieve a significant reduction in coupling relative to non-optimized placements, with comparable overall performance. Installed far-field radiation characteristics are further evaluated to verify that the optimized solutions preserve, and in some cases improve, the omnidirectional coverage required for airborne VHF communication. The proposed workflow provides a practical, simulation-driven framework for electromagnetic compatibility (EMC)-oriented antenna integration on complex aircraft platforms. Full article

Multiband antennas have high value within the telecommunications field, including satellite applications. Among the different solutions proposed in the scientific literature, a lack of attention is reserved for fractal antennas, which represent a very appealing and simple option to obtain a multiband behavior. In this paper, a printed monopole, resulting from the combination of the Sierpinski gasket and the Von Koch snowflake fractals, is proposed. The antenna takes advantage of the two fractal geometries to achieve multiband operation and miniaturization, both desirable features in antennas for satellite applications. The proposed fractal monopole works in S-band (2.75–3.96 GHz), C-band (6.15–7.6 GHz), and X-band (11–11.15 GHz) for satellite communication, with a realized gain of 2.8, 4.02, and 3.75 dBi; a high efficiency (up to 97%); and a compact size (0.52λ₀ × 0.3λ₀ × 0.006λ₀ at the lowest operating frequency). Full article

This paper presents a novel broadband circularly polarized optically transparent monopole antenna using indium tin oxide (ITO) and PMMA. The proposed design successfully integrates ultra-wideband circular polarization characteristics with exceptional optical transparency. The antenna, constructed with a three-layer configuration utilizing ITO films as both the radiating patch and ground plane, along with transparent PMMA serving as the substrate, features compact dimensions of 40 × 40 × 1 mm³. By leveraging a co-optimized design incorporating a slotted hexagonal-ring radiating patch, triangular perturbation ground plane, and stepped-impedance feeding structure, the antenna achieves a circularly polarized operating bandwidth of 2.8–6.6 GHz (fractional bandwidth of 77.9%), with an axial ratio < 3 dB and return loss < −15 dB. The experimental findings exhibit strong consistency with the simulations, illustrating a high level of visible-light transmittance and radiation patterns characterized by right-hand circular polarization in the positive z-axis direction (+z) and left-hand circular polarization in the negative z-axis direction (−z). This innovative antenna shows great potential for applications in smart windows, display integration, and 5G communication systems. Full article

This study presents the design, optimization, and experimental validation of a dual-band dielectric monopole antenna. The proposed antenna structure consists of three concentric cylindrical dielectric layers, each with independently tunable permittivities and radii. This configuration allows the effective control of electromagnetic performance over distinct frequency bands. To determine the optimal geometric and material parameters, the bio-inspired Honey Bee Mating Optimization (HBMO) algorithm is employed. The optimization process simultaneously maximizes antenna gain and minimizes reflection coefficient in the X and Ku bands. A cost function incorporating both gain and impedance matching criteria is formulated to achieve well-balanced solutions. The final antenna prototype was fabricated using a fused deposition modeling (FDM)-based 3D printer, where the dielectric properties of each layer are adjusted through variable infill rates. Simulated and measured results confirm stable dual-band operation with reflection coefficients below −10 dB, while the maximum in-band realized gains reach approximately 6.6 dBi in the X-band and 7.1 dBi in the Ku-band. These findings demonstrate the effectiveness of the proposed optimization approach and validate the feasibility of using 3D-printed dielectric-loaded structures as an efficient solution for high-frequency and space-constrained communication systems. Full article