Search Results (2,674)

Antenna–surface coupling is a key factor controlling the quality of Ground Penetrating Radar (GPR) data, governing the efficiency of electromagnetic energy transmission into the investigated medium. In cultural heritage applications, however, direct antenna contact is often not feasible due to the fragility of decorated surfaces, requiring non-contact configurations whose impact on high-resolution imaging remains insufficiently quantified. This study investigates the effect of antenna coupling on high-resolution 3D GPR imaging of concealed masonry at Pompeii through electromagnetic simulations and a controlled in situ comparison of contact and non-contact acquisitions on a plastered wall. The experimental campaign was conducted at the House of the Red Walls (VIII, 5, 37) on an opus mixtum masonry, selected as the most geometrically and electromagnetically challenging test case among regular Pompeian construction techniques. A 3 GHz antenna was employed, and three acquisition configurations were analysed: direct contact, and non-contact setups with antenna elevations of 3 cm and 5 cm. The results show that even moderate antenna elevation significantly reduces coupling efficiency at the air–plaster interface, leading to a progressive degradation of imaging performance. While the overall masonry arrangement remains recoverable in all configurations, increasing stand-off distance reduces the detectability of individual units and degrades geometric accuracy, with vertical mortar joints being the most affected elements. These findings demonstrate that, given the combined electromagnetic and geometric characteristics of the construction materials used at Pompeii, near-contact GPR acquisition is required for reliable imaging of masonry arrangement under the investigated conditions, highlighting the critical role of antenna coupling in high-frequency GPR surveys of fragile architectural surfaces. Full article

This paper presents the design and analysis of a graphene-based patch antenna for terahertz (THz) communication applications. The proposed antenna has a compact footprint of 60 μm × 60 μm and employs an inset-fed modified graphene patch to achieve dual-band operation. The antenna exhibits resonances at 0.58 THz and 1.01 THz, with |S₁₁| below −30 dB, indicating excellent impedance matching. The tunability of graphene is investigated by varying the chemical potential and relaxation time, and the antenna performance is optimized accordingly. It is observed that higher values of chemical potential and relaxation time enhance the surface conductivity of graphene, resulting in improved impedance matching and radiation efficiency. A detailed parametric study is also carried out by varying the dimensions of the slot etched on the patch. The results demonstrate that slot dimensions significantly influence both impedance matching and resonance frequency tuning. The antenna achieves a gain > 2.53 dBi and total efficiency exceeding 60% across both operating bands. The radiation patterns in both E- and H-planes are nearly omnidirectional at 0.58 THz and 1.01 THz, making the design suitable for near-field THz applications. The electromagnetic performance of the proposed graphene patch antenna is analyzed using CST Microwave Studio. Full article

Academic laboratories increasingly deploy DC motor-driven equipment, but wireless control faces two challenges: congestion in the 2.4 GHz band and the absence of application-layer confidentiality. This paper presents a 433 MHz LoRa-based wireless joystick control system with AES-128 confidentiality protection, validated using an ABU Robocon robot as a representative testbed. Performance was characterized outdoors across six Spreading Factors (SF7–SF12) under line-of-sight (LoS) and non-line-of-sight (NLoS) propagation (n = 6 per condition), and across three indoor campaigns (n ≈ 100 packets per condition) to quantify the gap between outdoor boundary estimates and indoor deployment. One-way ANOVA confirmed significant SF effects on latency, RSSI, and SNR (F = 10.4–5812, p < 0.001); normality and homogeneity-of-variance assumptions were formally tested, frequently violated for RSSI/SNR, and corroborated by Kruskal–Wallis tests, with large effect sizes (η² = 0.27–0.99). A preliminary low-antenna indoor test showed severe PDR degradation (as low as 14%), plausibly from ground-reflection multipath; elevating both antennas (≈70/60 cm) produced mixed, not uniformly improved, results. Indoor-NLoS testing showed low Spreading Factors failing almost completely beyond 5 m (SF7/SF8 near 0% PDR at 10–15 m) while SF10–SF12 remained robust (89–100%), a more consequential finding than outdoor boundary conditions (100% PDR at 5–15 m) suggest alone. Interference experiments characterized position-dependent and cross-Spreading-Factor resilience, with an explicit literature-grounded caveat rather than an unconditional quasi-orthogonality claim. SF10/SF11 with a 5 dBi antenna remains the best outdoor compromise (147–176 m range, 206–357 ms latency); indoor deployments require SF-specific de-rating and antenna-height practice. AES-128 added no measurable latency overhead. Contributions include a validated retrofit blueprint, a statistically grounded SF selection matrix spanning outdoor and indoor conditions, a practical antenna-height recommendation, and a controlled characterization of indoor interference resilience. The AES-128 ECB implementation provides confidentiality only, not authentication or replay resistance; limitations and a migration roadmap are discussed. Full article

During tunnel construction, ground-penetrating radar detection requires stable contact between the antenna and the tunnel wall, whereas manual operation is labor-intensive, risky, and difficult to maintain with consistent coupling. To improve automated tunnel surrounding-rock quality detection, this study develops an end-effector compliant control system for a tunnel inspection manipulator. A three-degree-of-freedom manipulator equipped with a passive compliant end-effector mechanism was designed, and an admittance controller was established to regulate the contact force between the radar antenna and the tunnel surface. To improve adaptability under irregular wall conditions, a fuzzy variable-damping strategy was introduced, in which the equivalent end-effector velocity and acceleration were used to adjust the damping coefficient online. The proposed controller was evaluated through MATLAB/Simulink simulations, indoor experiments with wall and ground irregularities, and field tests in an actual tunnel. Compared with fixed-damping admittance control, the proposed method reduced contact-establishment overshoot by 69.3% and inspection-stage force fluctuation by 36.49% in simulation. Indoor experiments further verified lower peak contact force and shorter settling time under different wall and ground conditions. Field tests at the tunnel crown and sidewall demonstrated that the radar antenna maintained effective wall contact. The results indicate that fuzzy variable-damping admittance control improves contact stability and practical applicability for robotic tunnel inspection. Full article

Carbon cloth is a lightweight and mechanically robust fibrous substrate with strong potential for value-added flexible electronic applications. In this study, carbon cloth/polypyrrole (CC/PPy) composites were fabricated via vapor-phase polymerization (VPP) and evaluated as radiating electrodes for flexible monopole patch RF antennas. By varying the polymerization time, the surface resistance and complex permittivity of the CC/PPy composites were systematically tuned, enabling simultaneous optimization of electrical conductivity and dielectric response. Among the prepared samples, the composite polymerized for 20 s exhibited the most balanced properties, with a sheet resistance of 1.86 Ω/sq, a real permittivity (ε′) of 5.78, and an imaginary permittivity (ε″) of 0.23. When applied as the antenna electrode, this material delivered a return loss of −34.81 dB, a radiation efficiency of 84.32%, a peak gain of 3.30 dBi, and a peak directivity of 3.91 dBi at 1.74 GHz. In addition, the antenna maintained stable performance after 5000 bending cycles, demonstrating excellent mechanical durability. These results show that simultaneous control of surface resistance and dielectric properties is critical for high-performance flexible RF electrodes and provide a practical surface-functionalization strategy for upgrading carbon-cloth-based fibrous materials into value-added electronic products. Full article

Future transportation networks may require aerial communication platforms capable of providing flexible and reliable services to vehicular terminals. In conventional unmanned aerial vehicle (UAV) communication systems, the antenna geometry is commonly treated as fixed, which limits the attainable directional gain when the relative geometry between the UAV and users changes significantly. This work considered a UAV equipped with a mechanically reconfigurable antenna array and studied its joint motion and transmission control under finite-blocklength communication. A sequential optimization problem was formulated to maximize the accumulated user throughput by jointly optimizing the UAV trajectory, the array orientations, and the transmit beamforming vectors, subject to the UAV kinematic constraints, the UPA orientation constraints, and the transmission energy budget. The resulting problem involves nonlinear coupling among platform motion, antenna pointing, beamforming, and finite-blocklength rate expressions, making conventional optimization computationally demanding. To obtain an adaptive control policy, a soft actor–critic-based deep reinforcement learning method was developed. The simulation results showed that jointly controlling the UAV mobility, array orientation, and beamforming improves the achievable finite-blocklength transmission performance compared with benchmark schemes, demonstrating the effectiveness of the proposed framework in enhancing reliable data delivery for UAV-assisted transportation infrastructure applications. Full article

Conventional antenna designs generally have fixed configurations and are difficult to assemble rapidly and flexibly. To address this limitation, this paper proposes a magnetic antenna building block that enables the rapid assembly of functional antennas. Based on this building block design, a kind of reconfigurable frequency scanning leaky wave antenna is implemented. The antenna module consists of the RF structure, dielectric housing, and embedded magnets. Magnets align and attach adjacent modules, while RF signals are transmitted through non-contact capacitive coupling interfaces and radiated by the RF structures on individual modules. The Port module, low-radiation module L, and high-radiation module H are designed. A variable number of cascaded modules can be rapidly cascaded through magnetic attachment to form different antenna arrays. The H module incorporates a pair of symmetric circular patches connected in parallel and exhibits stronger radiation characteristics than the L module, which does not include this parallel structure. Simulation and measurement results showed that the antenna arrays achieved effective port impedance matching in the C-band for cascades of the same type of modules and several mixed cascades of different types of modules. Far-field measurements also showed that arrays with different module combinations produced distinct far-field radiation patterns and allowed adjustment of the main beam gain and direction over 6.30–6.90 GHz. The main beam direction varied over a range of approximately 30°, and continuously covered the region around normal direction. The beamwidth varied with module types and the number of cascaded modules. The 3 dB beamwidth decreased from 48° to 21°, and the highest peak gain reached 6.98 dBi. The proposed magnetic antenna building block supports module cascading, combinations of different module types, and frequency scanning, providing a low-cost and flexible implementation of reconfigurable antenna arrays for communication and sensing applications. Full article

In reconfigurable array transmissions, a phased-array transmitter changes its characteristics, yet must still be able to control its transmission while optimizing its performance. To enable full reconfiguration while transmitting predictably, performing accurate, real-time measurements within the transmit chain is useful. This recently developed in-situ measurement approach, shown in multiple previous contributions, is summarized in this paper. It serves two purposes: (1) informing the real-time optimization algorithm whether changes in transmitter characteristics improve or worsen performance, and (2) updating the array calibration to obtain the desired transmit array pattern. This will enable real-time, “on the fly” optimizations of transmitters to coexist with other wireless devices in an increasingly congested spectral environment. A four-port coupler, with two monitoring outputs, is used to monitor the total voltage and current between a reconfigurable impedance tuner and the antenna in each element of a transmit array chain. Experimental work from the different prior contributions shows the overall trajectory, reliability, and proposed applications of this in-situ measurement technique. Less than 1 mV of error vector magnitude is shown in vector network analyzer methods compared with simulations using the in-situ coupler approach. The integration and calibration of a software-defined radio to perform antenna input current in-situ measurements has been implemented, with an average current error vector magnitude of 258 µA when comparing the software-defined radio measurements with simulations. Simulation results have shown that in-situ measurements can successfully correct input voltage waveforms for accurate directionally modulated transmissions, lessening reliance on fixed transmitter array pre-calibrations. Full article

The transition from early non-standalone 5G deployments to 5G Standalone and, more recently, 5G-Advanced has turned mobile networks into flexible, programmable infrastructures capable of supporting private, industrial, and research-oriented deployments for the development of beyond-5G applications and architectures. Evaluating these networks’ capabilities, however, remains challenging because commercial platforms often provide limited access to internal interfaces, radio parameters, and network measurements. This paper presents an open-source private 5G SA testbed for beyond-5G application validations built using Open5GS, srsRAN, Ettus USRP N310 software-defined radio, programmable SIM cards, and commercial 5G customer-premise equipment. The platform is deployed in a semi-anechoic chamber. End-to-end operation is validated through subscriber registration, authentication, PDU session establishment, and external data connectivity. The performance of the implemented 5G network is evaluated using throughput, block error rate, modulation and coding scheme, and gNB trace logs. Unlike previous open-source 5G testbeds that primarily use RF waveguides, individual network components, or a limited set of radio configurations, the proposed platform combines COTS SIM-based UE operation with a controlled over-the-air evaluation of FDD/TDD and multiple antenna configurations and correlates application-level throughput with internal gNB radio metrics. For FDD downlink operation, the average throughput increased by approximately 74% from 1 × 1 to 2 × 2 and by a further 57% from 2 × 2 to 4 × 4, although the additional peak-throughput gain from 2 × 2 to 4 × 4 remained limited. The platform provides a reproducible environment for validating beyond-5G mechanisms, comparing network configurations, and studying the behavior of future open-source 5G SA systems under controlled conditions. Full article

As implantable medical devices become increasingly miniaturized while demanding higher power levels, longer lifetimes, and larger data throughput, conventional powering and communication approaches are reaching their practical limits. Consequently, wireless power and data transfer have emerged as key enabling technologies for next-generation implantable systems. However, designing wireless links that simultaneously satisfy these requirements while remaining compact, efficient, and safe remains a significant challenge. To address this, this paper introduces an exploration and evaluation framework for selecting and co-designing short-range wireless power and data transfer technologies in medical devices such as cochlear and retinal implants. Guided by application requirements and relevant safety standards, the framework evaluates candidate technologies based on their operating principles, performance, and integration complexity. Based on this analysis, resonant inductive coupling is identified as the preferred approach for wireless power transfer, while both coil-based and antenna-based solutions are considered for wireless data transfer. Additionally, the paper compares architectures for integrated wireless power and data transfer, including both single- and multiple-link designs, and reviews strategies for uplink communication. The framework aims to guide the development of future sensory neuroprostheses that are smaller, safer, and capable of higher performance through optimized wireless link design. Full article

A low-profile inverted ridged-waveguide slot array antenna with asymmetric feed is proposed for two-dimensional (2D) wide-angle scanning spaceborne synthetic aperture radar (SAR) applications. The inverted ridge and asymmetric feed structure enables broad-wall radiating slots without lateral offset, achieving an ultra-low profile of 0.28λ₀, significantly lower than typical ridged-waveguide slot arrays for 2D wide-angle scanning applications, while supporting a compact inter-element decoupling configuration. H-shaped slots are further introduced to enhance the structural robustness of large-scale lightweight phased arrays without radiation performance degradation. The fabricated antenna element attains a wide relative bandwidth of 23.16% in the X-band. In array operation, the active voltage standing wave ratio (VSWR) remains below 2.0, and the phased array achieves 2D beam scanning coverage of ±55° in elevation and ±15° in azimuth. Full article

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

The rapid development of wireless communication systems has increased the complexity of smartphone antenna design. Modern terminals are required to simultaneously support Sub-1 GHz cellular bands, 5G New Radio (NR), millimeter-wave communication, satellite links, and emerging sensing services within limited physical space. As a result, multiband operation has become a central challenge for mobile terminals. This paper reviews the recent research advances in multiband smartphone antennas, organized according to the evolution from single-antenna to multi-antenna architectures and including both Sub-6 GHz and millimeter-wave applications. Single-antenna Sub-3 GHz techniques, multiband multi-antenna systems, dual-band millimeter-wave antennas, and integrated Sub-6 GHz/millimeter-wave architectures are systematically summarized. The key technologies, including multi-mode cooperation, characteristic-mode design, multiple-input multiple-output (MIMO) decoupling, and shared-aperture integration, are discussed. The emerging B5G/6G-oriented technologies are also highlighted. This review provides an overview of current design strategies and future trends for next-generation multiband smartphone antennas. Full article

A compact 24 GHz FMCW radar board was evaluated for low-speed bicycle and small-vehicle sensing under strict memory and latency constraints. The hardware uses only 30 MHz modulation bandwidth, giving a nominal range resolution of about 5.0 m and a Doppler-bin spacing of about 2.57 m/s. Its small, incompletely calibrated antenna path also prevents any claim of high-angular-resolution imaging-radar performance. Within this constrained platform, the measured sequences reveal four coupled failure modes: static reflectors remain prominent in the range–Doppler map, useful low-Doppler responses are easily lost near the processed spectral boundary, weak plots do not always initiate a track, and short echo gaps can break otherwise continuous trajectories. To address these limitations, we combine frame-differential range–Doppler enhancement, quadrant-aware boundary-adaptive CA-CFAR, physically gated seed-growing initiation, and finite-frame retained Kalman tracking with SNR-weighted updates. In addition to natural bicycle and small-vehicle measurements, a labeled synthetic 64 by 32 range–Doppler benchmark is used to report Precision, Recall, F1-score, ROC/AUC, detection probability, and false alarms per frame for multiple CFAR variants. Public-radar tracking metrics are also reported on RadarScenes, a public RADIATE foggy sample, and nuScenes mini radar-only sequences with a bounded-approximation JPDA baseline. These public-radar results evaluate tracker-lifecycle and data-association behavior under public target-center observations; they are not presented as full validation of the board-specific RD-to-track pipeline. The evidence supports a bounded embedded-processing claim for this low-resolution board, not general applicability to high-resolution imaging radar systems. Full article

With the rapid development of wearable body-centric wireless systems, there is a growing demand for textile antennas with stable on-body performance, low profile, flexibility, and garment compatibility. Textile metamaterials provide an effective approach to address the limitations of conventional textile antennas by regulating antenna–body coupling, backward radiation, surface-wave propagation, frequency selectivity, local resonance, and polarization. Although existing reviews have discussed the mechanisms and structures of metamaterials, systematic discussions that connect metamaterial structures with textile materials, fabrication, and performance remain limited. This review summarizes representative metamaterials used in textile antennas and analyzes their roles in gain enhancement, SAR reduction, miniaturization, multiband operation, and polarization improvement. Common substrates, spacers, and conductive materials are further reviewed, together with fabrication methods such as lamination, embroidery, sewing, weaving, knitting, printing, coating, and laser patterning. Current studies indicate that material variability, conductor loss, fabrication tolerance, layer alignment, deformation stability, and garment integration still restrict practical application. This review is expected to provide a reference for the design and realization of reliable metamaterials for textile antennas. Full article