Search Results (273)

Traditional over-the-air (OTA) testing typically requires the device under test (DUT) to be positioned at the geometric center of the anechoic chamber, which limits the flexible evaluation of modern wireless terminals. Although the spherical vector wave (SVW) method provides a rigorous electromagnetic mode expansion, its direct use in eccentric testing scenarios is prone to coefficient-domain overfitting. In the conventional coefficient-domain formulation, the increased involvement of high-order evanescent modes can lead to overfitting of physically insignificant coefficients, resulting in unstable and oscillatory reconstruction. To explain this behavior, an analytical periodicity model is developed and validated by numerical simulations, showing good agreement across all tested configurations. To overcome this limitation, this paper develops a unified 3D eccentric spatial–spectral composite operator for eccentric field synthesis by directly incorporating the three-dimensional offset into the field evaluation process. The proposed operator maps probe excitation weights to the translated 3D local test-zone field samples, thereby reformulating the synthesis problem from coefficient-domain fitting to field-domain matching. This field-domain formulation naturally downweights high-order modal components with negligible local-field contributions, thereby improving numerical stability. Numerical simulations in a 3D multi-probe anechoic chamber (MPAC) demonstrate that, under significant eccentric conditions, the conventional SVW method essentially fails, while the plane wave synthesis (PWS) method achieves less accurate reconstruction than the proposed scheme. In contrast, the proposed scheme maintains stable, oscillation-free reconstruction and consistently outperforms PWS by 5 to 15 dB across all evaluated scenarios. This work provides a promising solution for flexible 3D OTA evaluation of large-scale wireless terminals. Full article

Considering the issue of noise generated by equipment that requires high air permeability for operation, a louvered noise barrier was designed. In accordance with sustainability principles, hemp fiber was used in the louvers. The aim of this experimental research was to investigate the effectiveness of the louvered noise barrier in a semi-anechoic chamber and to evaluate the influence of the number of louvers, the angle of inclination of the louvers, and the hemp fiber density on the performance of the barrier. An investigation of the barrier in a semi-anechoic chamber was carried out, using the rotating microphone method. The louvers in the barrier were tilted at angles of 0, 15, 30, or 45 degrees, and the density of fiber used in the different structures was 50, 100, 150, or 200 kg/m³. The highest insertion loss (IL) of the barrier reached 18.13 dB, and the sound reduction index (R′) reached up to 23.0 dB. The highest determined weighted sound reduction index (R′w) was 14.1 dB, and the equivalent sound level loss (LAeq) reached 9.9 dB (A). Full article

High-resolution soil moisture monitoring in a lysimeter requires precise Ground-Penetrating Radar (GPR) systems that can provide clean time-domain data for a Full-Waveform Inversion (FWI) algorithm. Using high-speed Radio Frequency System-on-Module (RFSoM) devices provides flexibility in signal generation. To optimize such a system, an appropriate transmit waveform and processing pipeline need to be selected. This paper presents a performance evaluation of three GPR waveforms—impulse, Stepped-Frequency Continuous Wave (SFCW) and non-linear Frequency-Modulated Continuous Wave (FMCW/chirp)—on the same hardware setup. To ensure a fair comparison, all waveforms were tested under an identical total measurement time. Numerical simulations were performed using an electromagnetic model of the system. Physical validation was conducted in an anechoic chamber using a 4 GS/s RFSoM setup and planar elliptical dipole antennas. Simulations showed that both sinewave-based methods provide better signal-to-noise ratios (SNRs) than the impulse GPR, with the non-linear chirp achieving the best results (20.7 dB improvement compared to impulse). Experimental measurements supported these results, showing better SNR across the frequency band for the SFCW and chirp waveforms. Because of its high SNR and simple hardware implementation, the non-linear chirp was identified as the most suitable waveform for this RFSoM-based GPR system. Full article

A low-profile, low radar cross-section (RCS) omnidirectional metasurface antenna is investigated and proposed in this letter. The antenna consists of a top circular patch, a three-layer dielectric substrate, a full metal ground, a multi-layer polarization conversion metasurface, and four short vias for connecting the top patch to the ground. Wideband impedance matching is achieved by modifying an F-shaped feeding structure. The broadband RCS reduction is realized by loading the antenna with the polarization conversion metasurface (PCM) in an appropriate array configuration. The antenna prototype has been fabricated and measured in an anechoic chamber. Experimental results illuminated that the antenna features a low profile of 0.051λ₀ (λ₀ is the wavelength at 2.35 GHz) and a 10 dB impedance bandwidth of 2.11–2.62 GHz (a fractional bandwidth of 21.56%). Significantly broadband RCS reduction is achieved from 7.05 to 16.96 GHz, with a maximum reduction of –28 dB and an average reduction of –12.51 dB. Full article

Forward scatter radar (FSR) can enhance target echo signal power by exploiting the sharp increase in radar cross-section (RCS), and has been widely studied in passive radar target detection. Traditional FSR detectors operate based on the shadowing effect that occurs when a target crosses the baseline. However, when satellite transmitters are used, the probability that a target’s trajectory intersects with the baseline in three-dimensional space approaches zero. Therefore, shadowing is difficult to occur. A moving-target detection method using weighted time-frequency (TF) entropy fusion is proposed in this paper for scenarios where targets move near the baseline. First, an echo signal model is established to show that the frequency change can be approximated as linear within a short time. Then, four TF entropy features are extracted from the received signal and linearly weighted to form the test statistic. The weights are optimized using the Nelder–Mead algorithm, with the objective of maximizing the average detection probability. Finally, the effectiveness of the proposed algorithm is verified through simulations and anechoic chamber measurements. The weighted fused TF entropy achieves a higher detection probability than any single TF entropy. Compared with the energy detector, the required signal-to-noise ratio (SNR) is reduced by about 3 dB to achieve the same detection probability at a false alarm probability of 10⁻³. Full article

This work presents a spiral-loop sequential-phase (SLSP)-fed radial-sector patch circularly polarized (CP) antenna for S-band CubeSat platforms. The architecture stacks three RO4003C substrates in an aluminum enclosure: a lower layer with tapered-blade parasitic elements, a middle layer with the SLSP feed and four radial-sector patches, and an upper tilted hexagonal metasurface superstrate separated by an air-gap. Characteristic mode analysis is used to realize an orthogonal modal pair. A prototype integrated on a CubeSat structure was measured in an anechoic chamber and validated under vibration and thermal-vacuum testing per ECSS/NASA practices. The antenna achieves a measured return loss bandwidth of 2–2.34 GHz, an axial ratio bandwidth of 2.04–2.25 GHz, and a maximum gain of 7.24 dBic at 2.18 GHz. The metasurface and parasitic elements enhance bandwidth while maintaining boresight CP. The novelty lies in the integration of SLSP-fed radial-sector patches with a tilted hexagonal metasurface superstrate and tapered-blade parasitic elements within a compact stacked configuration, making the proposed antenna well suited for CubeSat S-band applications. Full article

This paper presents the fabrication and experimental characterization of a 316L stainless-steel WR-90 waveguide horn antenna manufactured using selective laser melting (SLM) and operating across the X-band (8.2–12.4 GHz). The antenna is designed based on standard WR-90 waveguide theory and incorporates a coaxial-to-waveguide transition and a flared radiating aperture to achieve stable aperture-based radiation. Full-wave electromagnetic simulations are performed to establish baseline impedance, radiation pattern, and gain performance prior to fabrication. The SLM-fabricated prototype is evaluated through reflection coefficient, radiation pattern, and realized gain measurements conducted in an anechoic chamber. Measured results confirm stable impedance matching across the entire band, with |S₁₁| below −10 dB and a minimum of −22.34 dB near 10.1 GHz. The radiation patterns closely follow simulation predictions, with half-power beamwidth deviations below 4%. The realized gain increases from 11.2 dBi to 15.8 dBi across the band, with simulation–measurement deviation decreasing to within 0.5 dB above 10 GHz. Rather than focusing on antenna design novelty, this work employs a standardized WR-90 horn antenna as a benchmark structure to isolate fabrication-induced effects. A quantitative performance analysis is introduced by converting the gain deviation into an equivalent efficiency reduction, providing a practical framework for evaluating fabrication-induced electromagnetic degradation in SLM-fabricated waveguide components. Full article

The growing adoption of Low Earth Orbit (LEO) constellations in telecommunications demands antenna systems capable of tracking rapidly moving satellites and performing frequent link handovers. Conventional planar phased arrays, typically used in ground terminals, offer limited scan coverage, which can degrade communication with low elevation satellites. This work evaluates non-planar antenna array configurations to extend scan coverage in array systems with beamforming capability. Four- and five-element non-planar arrays were analysed and compared with equivalent planar structures. The proposed geometries achieved coverage improvements of 39.1% and 32.1%, respectively. Prototypes were fabricated and experimentally characterized in an anechoic chamber, yielding results indicating strong potential (6.5% to 30.6% more coverage) for further scan performance in beamforming systems. Full article

The problem of performance degradation in current sound source localization algorithms under reverberant and noisy environments remains a critical challenge. Consequently, this paper introduces a novel approach to estimate the 3-D position of sound sources directly from raw audio signals using an artificial neural network (ANN), which improves the performance of sound source localization algorithms under reverberant and noisy environments. Instead of relying on handcrafted features, raw audio signals recorded by a tetrahedral stereo microphone array are fed directly into the ANN. This design eliminates spatial symmetry issues found in 2-D microphone arrays and enhances 3-D localization accuracy. Inspired by human auditory systems, a convolutional layer is added after the input layer to simulate frequency analysis to search localization cues in different frequency bands. Furthermore, the proposed algorithm incorporates residual connections (RC) and squeeze-and-excitation (SE: an attention mechanisms). Residual connections introduce raw features into deeper network layers to prevent localized information loss caused by excessive network depth, while also enabling improved model training stability. The attention mechanism dynamically adjusts weights across and within channels, suppressing interference while enhancing localization-critical cues, thereby playing a pivotal role in boosting the algorithm’s reverberation and noise resistance. Experimental results demonstrate significant improvements: in semi-anechoic chambers, the method reduces localization errors by 0.2 m and increases accuracy by 10%; in conference rooms, errors decrease by 0.26 m with a 21% accuracy gain. These outcomes conclusively validate the effectiveness of the proposed approach in enhancing robustness against reverberation and noise in sound source localization systems. Full article

To evaluate the performance of a printed log-periodic dipole antenna (PLPDA) in outdoor environments, we present unmanned aerial vehicle (UAV)-based antenna measurements conducted in the far-field region. Non-tethered UAV flight operations were achieved by configuring commercially available UAVs separately as a transmitter (TX) and as a receiver (RX). UAVs configured in non-tethered mode provide flexibility in terms of altitude maintained by the UAV from the ground level. The TX section of the UAV consists of a portable signal generator and a PLPDA configured to transmit signals with an output power of +15 dBm at 0.8 and 3.5 GHz. Similarly, the RX section of the UAV is equipped with a real-time spectrum analyzer and an identical PLPDA. Using these two UAVs in TX and RX modes, the radiation pattern of the PLPDA was obtained in the azimuth plane. Since two identical PLPDAs were used, the realized gain of the PLPDA is evaluated using the two-antenna gain method. The test scenario involved the TX UAV hovering at the center while the RX UAV followed a circular trajectory around it. A comparison between the UAV measurements, anechoic chamber measurements, and simulated data demonstrates good agreement, validating the reliability of the measurements. Full article

We propose a coupling-aware equivalent source reconstruction framework for reproducing complex three-dimensional electromagnetic (EM) environments inside an anechoic chamber. A measured or simulated target field is represented by a finite set of physically realizable equivalent source antennas whose positions and complex excitations are identified by solving a nonlinear high-dimensional inverse problem. To ensure physical fidelity, the forward model explicitly accounts for mutual coupling through a full-wave Method-of-Moments (MoM) formulation, avoiding the inaccuracies of idealized uncoupled superposition. The inverse problem is efficiently solved using a hybrid evolutionary optimization scheme that combines an adaptive differential evolution strategy with stagnation-triggered CMA-ES refinement, augmented by a lightweight surrogate-based pre-screening to reduce expensive full-wave evaluations. The optimized source configuration is directly deployed in a microwave anechoic chamber, where the reconstructed field is measured on an observation plane and compared against the target field. The experimental results demonstrate close agreement in both amplitude and spatial distribution, while the proposed optimization pipeline substantially reduces the number of full-wave evaluations required for convergence. This work enables accurate repeatable chamber emulation of outdoor or in situ EM scenarios for robust system-level testing and evaluation. Full article

In fire emergency ventilation systems, EC (Electronically Commutated) internal-rotor axial fans are critical devices, but their high-speed operation generates aerodynamic noise often exceeding 90 dB (A). While struts are core structural components regulating flow field stability, their specific geometric impact on trailing-edge vortex shedding and noise generation mechanisms remains unclear. This study investigates three strut configurations: a hexagonal annular type, a hexagonal double-ring type, and a three-pronged type. A coupled numerical model was established using Large Eddy Simulation (LES) and the Ffowcs Williams and Hawkings (FW-H) acoustic analogy. The Q-criterion was employed to analyze vortical structures, with numerical predictions validated against experimental measurements in a semi-anechoic chamber. The results quantitatively demonstrate that optimizing the strut geometry significantly mitigates unsteady flow separation. The three-pronged strut (Model C) effectively dispersed high-velocity airflow, reducing the peak turbulent kinetic energy (TKE) at the inlet by 30% compared to the original design (Model a). Furthermore, Model C achieved a 6.7 dB reduction in the sound pressure level at the blade-passing frequency (BPF), alongside a 14.1% reduction in pressure pulsation amplitude near the blade tip. Structural optimization of struts enables synergistic control over turbulence distribution and pressure fluctuations. By disrupting the phase coherence of shed vortices, the optimized design fundamentally suppresses aerodynamic noise, advancing axial fan design toward precise quantitative aeroacoustic optimization. Full article

This study investigates the sound insulation performance of an anechoic chamber, exploring the influence patterns of different multilayer material combinations on wall sound insulation characteristics. Based on sound transmission theory, a predictive model for multilayer material wall sound insulation was established. The finite element method was employed to simulate the sound propagation characteristics of walls and glass doors with various material combinations. After validating the simulation results through a double-room method experiment, the material combination scheme for the anechoic chamber walls and glass doors was optimized. Based on this, a 1000 mm × 1000 mm × 2300 mm soundproof room prototype was designed and constructed. Its sound insulation performance under reverberant conditions was tested using the insertion loss method and compared with simulation data. Simultaneously, a hybrid calculation method combining low-frequency finite element analysis with high-frequency statistical energy analysis enabled precise and efficient prediction of the overall sound insulation performance of the soundproof room. Research revealed that single-pane glass with thicknesses between 5 and 20 mm conformed to the mass law, with sound insulation increasing by an average of 0.8 dB per additional millimeter. The 10 mm single-pane glass emerged as the optimal choice for the soundproof room’s glass door due to its ideal thickness and excellent low-to-mid-frequency sound insulation. The optimized wall structure featured compact thickness, outstanding low-frequency sound insulation, and balanced mid-to-high-frequency performance. Simulation and experimental results for the core frequency range of 63–1000 Hz showed high consistency, which validates the reliability of the theoretical model and simulation methodology within this frequency band. The deviation of simulation results from experimental data in the frequency range above 1000 Hz is mainly caused by acoustic leakage due to experimental sealing defects, and the high-frequency simulation results are only used for trend analysis rather than conclusion support. This study identifies the optimal multi-layer material combination for soundproof rooms, providing practical material strategies for acoustic design. It also reveals the sound insulation mechanisms of multi-layer composite structures. The findings offer significant reference for optimizing soundproofing materials and structures in architectural acoustics and transportation noise control. Full article

Wind-induced noise remains a critical engineering challenge for MEMS microphones in compact consumer electronics such as smartphones, where spatial constraints limit conventional noise control solutions. This study experimentally investigates the suppression of flow-induced wind noise by a straight tube serving as the front cavity of a microphone, using a precision measurement microphone for data acquisition. Controlled experiments were conducted in both a flow duct for parametric isolation and an anechoic chamber for real-world validation. Results demonstrate a strong diameter-dependent effect: for a 1 mm diameter, increasing tube length significantly reduces noise power spectral density and steepens high-frequency roll-off via enhanced internal viscous and thermal dissipation. This effect weakens for a 2 mm diameter and becomes negligible for a 3 mm diameter, where noise is dominated by external flow excitation at the tube inlet rather than internal propagation. Therefore, extending tube length is an effective noise control strategy only for small-diameter cavities. Furthermore, while increased wind speed and oblique incidence elevate PSD, a longer tube reduces this sensitivity. Because acoustic transmission loss—including potential effects like aperture diffraction and impedance mismatch—was not measured, any resulting improvement in the effective signal-to-noise ratio is strictly presented as a hypothesis requiring future electroacoustic validation. The consistent findings across both experimental environments provide clear design guidance: for compact MEMS microphone systems in portable devices, elongating the front cavity is a viable passive noise control method only when the cavity diameter is sufficiently small (<2 mm). This offers a practical, space-efficient alternative to traditional windscreen-based approaches in portable devices. Full article

Unmanned aerial vehicle (UAV) applications are growing fast in different sectors, such as agricultural, commercial, academic, leisure, and health fields. However, drones pose a significant threat to public safety due to their ability to transmit information, particularly when used in an unauthorized or malicious manner. In fact, in order to protect citizens’ privacy and prevent accidents in high-traffic areas due to poorly controlled flights, no-fly zones for drones have been established in the legislation of a number of countries. Most common UAV detection techniques are based on radio frequencies, which identify drones and their models by monitoring radio frequency signals. However, differentiating between multiple UAVs of the same model is their main limitation. This article fills this gap by proposing a method for physically tracking the communication frames of a registered UAV in the presence of another UAV of the same model. A measurement campaign was conducted to collect real-world RF communication signals from two DJI MAVIC 2 Zoom, two DJI Air2S, and two DJI Phantom drones. This measurement was performed inside and outside an anechoic chamber in order to study the UAV’s communication without any interference and in the presence of other communications. Through detailed statistical analysis, we characterized features such as communication duration, time intervals between communications, signal strength, and patterns in communication timing sequences. Our analysis revealed unique, identifiable patterns for each UAV, even within identical models. Based on these results, we developed an automated system that links communication frames to the corresponding registered drones. The proposed method fills gaps in drone detection and surveillance models, providing valuable information for applications in the fields of security and airspace management. This research lays the foundation for drone identification solutions, thereby addressing a major limitation of current detection technologies. Full article