This study presents millimeter-wave propagation measurements at 60 GHz conducted in a reverberation chamber to emulate realistic multipath-rich indoor environments. Both line-of-sight (LOS) and non-line-of-sight (NLOS) scenarios are investigated using commercial off-the-shelf devices. The impact of stirring conditions and lossy environments is evaluated through key performance indicators, including Received Signal Strength Indicator (RSSI), Signal-to-Noise Ratio (SNR), Modulation and Coding Scheme (MCS), and throughput. Results show that mechanical stirring speed and the placement of absorbing materials significantly affect channel characteristics and system performance. In NLOS conditions, multipath propagation dominates, where dynamic beamforming demonstrates improved robustness. In contrast, LOS scenarios are highly sensitive to blockage, leading to notable performance degradation. Overall, the findings confirm that the reverberation chamber is an effective platform for over-the-air testing and characterization of 60 GHz wireless systems, offering valuable insights into system behavior under complex indoor propagation conditions relevant to future 5G and 6G deployments.

This paper presents a wideband circularly polarized (CP) antenna featuring a significantly enhanced front-to-back ratio (FBR). The proposed design employs a composite structure that integrates a dipole with a loop resonator and is fabricated using a multilayer architecture. The top layer is a dielectric substrate loaded with a cyclic zigzag patch. The middle layer contains an L-shaped radiating patch with etched rectangular grooves, and the bottom layer comprises a metal ground plane and surrounding vertically tilted-slot fences. Circular polarization is achieved by exciting orthogonal degenerate modes via strategic rectangular-groove perturbations that work in concert with the loop resonator's inherent asymmetric current path. The tilted-slot fences, in conjunction with the zigzag patch layer, function collectively to suppress backward radiation and improve the FBR. Measured results demonstrate that the antenna achieves a 3 dB axial ratio (AR) bandwidth of 54% from 2.45 to 4.3 GHz, a stable FBR of more than 27.5 dB with 2.5 dB variation, and a peak gain of 9.3 dBic. This design offers a high-performance, planar antenna solution well-suited for satellite communication and radar systems.

This study proposes a high-performance miniaturized wideband circularly polarized (CP) metasurface (MTS) antenna for WLAN and 5 GHz wireless communication systems. The design innovatively utilizes a hybrid embedded structure, where regular octagonal patches are incorporated into the gaps of modified X-shaped primary radiating elements to increase edge capacitance and lower resonant frequency, thereby achieving antenna miniaturization. To effectively excite the orthogonal degenerate modes required for CP radiation, a characteristic mode analysis (CMA) was employed to guide the design of the feed network. A feeding structure consisting of a hook-shaped microstrip line and a symmetrical stepped cross-slot is designed to achieve CP excitation via a 90˚ phase delay introduced by path length differences. Measured results demonstrate that the antenna achieves a -10 dB impedance bandwidth of 34.2% (4.38-6.19 GHz) and a 3 dB axial ratio (AR) bandwidth of 23.9% (4.68-5.95 GHz). Regarding radiation characteristics, the radiation efficiency remained stable above 75%, and the peak realized gain reached 5.26 dBic. The experimental results verified that the proposed design achieved stable CP and radiation performance within a miniaturized footprint.

Conventional fiber-optic measurement systems for pulsed electromagnetic fields are limited by power-supply instability due to the temperature sensitivity of photocells. To address this issue, we developed a highly reliable broadband fiber-optic transmission system featuring a hybrid power supply. In our design, a lithium battery serves as the primary power source for the optical transmitter, while a compact photocell provides short-term supplemental power and simultaneously recharges the battery. An additional shunt resistor (5-50 Ω) is added to avoid damping oscillations. Results: The system achieves a -3 dB bandwidth from 5 Hz to 122 MHz. The optical transmitter volume is reduced to one-fifth of a previous design. Ten repeated electric-field measurements show relative errors below 3%. Conclusion: The proposed system offers stable operation, low power consumption, wide dynamic range, and strong anti-interference capability, making it well-suited for harsh electromagnetic environments.

This paper presents a high-performance energy-selective structure (ESS) design methodology based on a stacked slotline. By leveraging the unique characteristics of three-dimensional stacked structures, the method efficiently converts spatial waves into guided waves in slotline transmission lines, which can be tailored via lumped-circuit design to achieve precise energy-selective functionality. The proposed design approach systematically extends previous work by providing a clear theoretical foundation for decoupling and independently optimizing multiple ESS performance indicators. This allows the design of structures with flexibly selectable frequency bands and high shielding efficiency. Two prototypes were fabricated to validate the method. Prototype I targets bandwidth expansion, achieving an operational range from 2.2 to 8.2 GHz (115.4% relative bandwidth), with less than 1 dB insertion loss and over 10 dB shielding effectiveness across the band. Prototype II emphasizes shielding performance, reaching a shielding efficiency greater than 33 dB between 3.9 and 6.3 GHz, with a maximum of 40.3 dB. Both prototypes were fabricated and validated through experimental measurements, showing agreement with the simulation results. The performance of the two designed structures far exceeds other existing ESSs in terms of broadband or high shielding efficiency, indicating that the comprehensive design method has great potential to significantly improve the design of targeted technical specifications.

Investigations into the nature of electromagnetic fields produced by dipole sources over homogeneous flat ground or impedance surfaces date back many years. In general, at a long distance r from the source, the near-surface field is mostly contributed by the geometrical optics term (describing the radiation pattern), a guided wave, and the higher-order reactive contribution referred to as the Norton wave. In the special case of a perfect magnetic conductor interface, the first two terms vanish, so the residual Norton wave determines the steepest achievable field decay profile of r^-3/2 (for a two-dimensional horizontal magnetic dipole). In this letter, we reveal that in the presence of a nonlocal metasurface described by the second-order impedance boundary condition, the field decay can be further accelerated by suppressing the Norton wave (approaching the profiles r^-5/2 and r^-7/2 for electric and magnetic fields, respectively). In a proposed practical realization of a nonlocal metasurface, the effect is numerically verified and shown to reduce the edge diffraction effects by 10 dB for the shield diameter of only one wavelength, paving the way toward compact antenna systems.

Dopamine (DA) is a critical neurotransmitter whose abnormal levels are associated with neurological disorders, including Parkinson's disease, Alzheimer's disease, and schizophrenia. The development of sensitive and reliable detection methods is therefore essential for diagnosis and treatment monitoring. Here, we report a phase-interrogated surface plasmon resonance (SPR) biosensor based on a graphene oxide (GO)-functionalized glass/Ti/Ag/Al₂O₃/ZnSe multilayer platform. The high refractive index (RI) ZnSe layer confined the evanescent field through a waveguide-coupled mode, which produced a sharp resonance with a measured FWHM of 0.077°, a Q-factor of 799, and a figure of merit (FOM) of 1527 RIU^-1. The slight broadening relative to the simulated FWHM of 0.034° is consistent with practical fabrication imperfections and beam angular divergence, though sensor performance was not meaningfully affected. The bulk RI calibration with glucose solutions confirmed a phase sensitivity of 4.53×104 deg RIU^-1 and an angular sensitivity of 120.1°/RIU. For DA detection, the ZnSe surface was functionalized with (3-aminopropyl)triethoxysilane (APTES) and GO and then exposed to different DA concentrations from 1 pM to 10 nM. A semi-log linear fit over the range of 1 pM to 1 nM showed a sensitivity of 1.15°/decade (R² = 0.9547), and a Langmuir isotherm yielded a maximum phase shift of 3.74°, a dissociation constant of 10 pM with R² of 0.9987. The limit of detection was 2.17 pM, and the signal-to-noise ratios (SNRs) ranged from 1.12 at 1 pM to 11.52 at 1 nM. The intra-chip coefficients of variation remained between 0.70% and 2.47%. Beyond clinical diagnostics, this platform holds promise for pharmaceutical applications, including drug development, pharmacokinetic/pharmacodynamic profiling, and therapeutic drug monitoring, where reliable small molecule detection is increasingly required. This work, therefore, offers a straightforward, label-free route to picomolar DA detection with a clear path toward real-sample validation and selectivity assessment.

A compact, fractal-shaped, triple-band multiple-input multiple-output (MIMO) antenna integrated with a frequency-selective surface (FSS) to improve radiation characteristics is presented in this work. The proposed design employs a fractal-based radiating element to achieve multiband characteristics while minimizing the size. The four-port MIMO configuration is developed from a single-port radiator using an orthogonal arrangement to improve the port isolation. A central square slot is introduced to suppress mutual coupling by interrupting surface current paths, thereby improving inter-element isolation across all operating bands. To enhance the gain, a multi-resonant uniplanar frequency selective surface (FSS) is designed and positioned to act as a partially reflective surface. The FSS unit cell, modelled using an equivalent circuit approach, exhibits three distinct stopbands corresponding to the desired operating frequencies of 2.7-3.5 GHz, 5.5-8.4 GHz and 9.3-10.9 GHz. The combined antenna-FSS configuration, with the overall electrical size of (0.5×0.5×0.235)λ, demonstrates a gain improvement of 3-4 dBi in all bands, without compromising bandwidth. With three frequency bands of 2.5-3.875 GHz, 5.25-6.05 GHz and 8.6-10.6 GHz, the proposed MIMO antenna achieves good MIMO characteristics, making it suitable for modern high-speed wireless technologies including sub-6-GHz 5G (WiMAX), WLAN, and ISM bands.

This research proposes a microwave sensor based on a dual-split-ring-resonator (DSRR) structure designed for the detection of the permittivity of solid samples and defective materials. The DSRR structure was chosen because it has a high-quality factor Q, is highly sensitive to changes in permittivity, and is easy to integrate into a planar substrate. The designed sensor is fabricated using a Rogers RO5880 substrate having a dielectric constant ε_r of 2.2, tanδ of 0.0009, and a substrate thickness h of 1.58; the sensor operates in the frequency range of 1 GHz-2 GHz and adopts a dual-port configuration by observing changes in the transmission parameter S₂₁. The measurements used the perturbation theory method, where the resonance frequency shift occurs when a material is inserted into the sensor area. This sensor area is defined as the location of maximum electric field concentration within the resonator. Polynomial equations are derived for measurements on dielectric materials with known permittivity values ranging from 1 to 9.8. The proposed sensor demonstrates high performance, with a measured accuracy of 99.6%, a normalized sensitivity of 2.6%, and a frequency detection resolution (FDR) of 0.026 GHz. These results indicate that the sensor using the DSRR method with hole integration offers reliable and precise permittivity detection, particularly for detecting defects in materials.

As the need for rapid data transmission and dependable wireless networks grows, so does the need for advanced antenna technology. This has become a major focus of modern communication technologies. This paper describes the design of a 4-port multiple-input multiple-output (MIMO) microstrip patch working at 28 GHz in the Ka-band. This antenna is fabricated on a substrate measuring 21 × 21 × 3.97 mm³, composed of FR4, foam, and RT/Duroid 5880. It uses a microstrip feed. Performance enhancements are achieved by positioning the feeds orthogonally, incorporating a U-shaped slot into the MIMO antennas, and implementing a superstrate made of metamaterial (MTM) elements. Additionally, a single-layer MTM superstrate with rectangular slots is created to improve gain while keeping good impedance matching. The design process systematically improves gain and mutual coupling while keeping the overall size compact. The specific challenge addressed by the design is to improve peak gain and radiation efficiency by employing MTM elements operating at 28 GHz. The 4-port MIMO antenna achieves an impedance bandwidth (IB) of 27.11-29.21 GHz, with a peak gain of 14.05 dB, respectively. This antenna is used in next-generation communication systems, vehicular networks, and 5G systems.

This study presents a broadband, switchable, and bi-functional terahertz device based on the phase transition of vanadium dioxide (VO₂). When VO₂ is in the metallic state, the device operates as a linear polarization converter (LPC). When VO₂ transitions to the insulating state, the device functions as a broadband linear-to-circular polarization converter (LTC-PC). Numerical simulations are conducted to verify the device performance. To further optimize metamaterial performance and accelerate the design process, a deep learning framework that integrates convolutional neural networks (CNNs) and the Transformer architecture via an adaptive mechanism is proposed. Numerical simulations indicate that this LPC achieves a polarization conversion ratio (PCR) exceeding 90% across the 1.92-2.93 THz band and maintains angular stability for incidence angles up to 50°. The LTC-PC operates effectively within the 2.40-4.33 THz range. Featuring broadband operation and bi-functional capabilities, the converter holds significant potential for applications in terahertz imaging, sensing, solar energy harvesting, and communications.

A compact four-port circularly polarized multiple-input multiple-output (CP-MIMO) antenna with a dual-layer architecture is proposed for low-altitude communication applications. In compact MIMO arrays of CP-capable monopole elements, strong mutual coupling makes stable CP radiation difficult to achieve. To address this issue, the proposed antenna uses a lower layer for dual-polarized MIMO generation and an upper layer for polarization conversion. The antenna is fabricated on two FR-4 substrates with an overall size of 0.85λ × 0.85λ × 0.084λ. In the lower layer, a dual-polarized feed backplane (DPFB) forms a ±45° dual-polarized MIMO array with port isolation exceeding 17 dB. In the upper layer, a polarization conversion superstrate (PCS) converts the incident dual-polarized waves into CP radiation. The PCS extends the impedance bandwidth by 36%, from 7.55 to 10.08 GHz, and enables LHCP radiation with a 3 dB AR bandwidth of 8.22-8.89 GHz. A gain enhancement of 48% is also achieved. Measured results verify the design and show good MIMO diversity performance.

Accurate simulation of partially coherent imaging is crucial for computational lithography, with Abbe and Hopkins as the two main formulations being used. Although the two methods are equivalent in theory, practical simulators making independent choices between Abbe and Hopkins could hardly produce consistent results that match the desired accuracy owing to the inherently different ways of numerically representing, discretizing, and truncating the illumination source and lens pupil function, etc. Moreover, classical Hopkins models require prior construction and/or eigen decomposition of the high-dimensional transmission cross coefficient (TCC), the prohibitive costs of which hinder timely model verification. To address these challenges, we developed a unified Abbe-Hopkins formulation in conjunction with a TCC-free Hopkins pointwise sampler for efficient cross-model validation. Our formulation supports both Abbe and Hopkins modeling in a single unified framework, with the two simulation modes using exactly the same numerical representations of the illumination source and projection lens. Cross-model verification for randomly sampled points is performed efficiently by evaluating the Hopkins quadratic form through a fast Fourier transform of an image and a few pointwise multiplications between images, without ever explicitly constructing a TCC and eigen-analyzing it. Numerical tests show that the Abbe and Hopkins results agree up to the machine precision level.

An improved scattering (S-)parameters extraction method, based on the forward and backward propagating waves under oblique incidence on metamaterials (MMs), is proposed to accurately extract electromagnetic parameters for asymmetric uniaxial MMs in a broad frequency range. The proposed approach equivalently models asymmetric MMs as two isotropic media (distinct from the 3 × 3 matrix-form anisotropic medium). To validate the effectiveness of the proposed method, a low-thickness asymmetric absorptive frequency-selective surface (AFSS) and a high-thickness 7-layer absorber were designed, simulated, and analyzed.

This paper presents a wideband four-port microstrip antenna operating from 2.75 GHz to 6.75 GHz with frequency reconfigurability and controllable notch characteristics. The antenna employs an asymmetric radiating structure to realize circular polarization around 5.5 GHz, while multilayer graphene(MLG) pads are introduced to enable bias-controlled frequency tuning and adjustable band rejection. The four-port configuration, implemented on an RT/Duroid 5880 substrate (ε_r = 2.2, thickness = 1.6 mm), achieves inter-element isolation better than 20 dB without additional decoupling structures. The proposed design also exhibits strong diversity performance with an envelope correlation coefficient below 0.02 and diversity gain above 9.97 dB. The results demonstrate that the proposed antenna provides a compact and low-complexity solution for wideband and reconfigurable sub-6 GHz wireless communication applications.

We have developed a carbon nanotube organic silicone rubber (CNT-OSR) composite medium, composed of methyl trifluoropropyl silicone rubber as the matrix, with different mass fractions of carbon nanotubes added and formed through vulcanization using a bis (cyclopentadiene) vulcanizing agent. The CNT-OSR composite media with carbon nanotube contents of 2wt%, 5wt%, and 8wt% were tested, and the maximum absorption and shielding efficiencies of the media for terahertz waves in the 0.5-1.0 THz frequency range were found to be 69.77 dB, 76.28 dB, and 63.69 dB, respectively. Through impedance matching theory analysis, the absorption and shielding effectiveness of the medium for terahertz waves were confirmed. Additionally, the composite medium exhibits excellent hydrophobic properties. It provides a simple and feasible approach for developing lightweight, efficient, and multifunctional terahertz wave absorbing and shielding materials for the next generation of terahertz wireless communication.

The dielectric constant, which is the real part of the complex permittivity, of composite materials at microwave frequencies was investigated in this study. Ceramics of titanium dioxide, calcium titanate, and strontium titanate with high dielectric constants of 100, 170, and 300, respectively, were selected. Ceramic powders were spread in the polyethylene matrix to form composite samples. The dielectric constants of the composite samples were measured to determine their matching conditions with the mathematical curves of five well-known mixture equations. These five mixture rules were then applied to estimate the dielectric constants of the three selected ceramics from the measured dielectric properties of the composite samples with various volume percentages of ceramic fillers. The mathematical equations of the potential theory errors of the five mixture rules for the dielectric constant estimation were derived and discussed. One of the five rules was selected and modified to obtain a new empirical mixture equation. This proposed empirical equation can significantly improve the accuracy of dielectric constant measurements for the selected ceramic materials. An empirical mathematical relation of the new mixing rule with the dielectric constant of the ceramic is then concluded.

The design of large-scale coding metasurfaces poses significant computational challenges, often limited by the prohibitive time required for full-wave simulations necessary for optimization. This paper proposes an efficient design strategy based on a Hybrid Genetic Algorithm, validated through the design, fabrication, and characterization of an X-band metasurface for Radar Cross Section reduction. The proposed design strategy relies on a two-stage optimization process: a fast pre-optimization phase, based on the analytical Huygens-Fresnel principle, generates a preliminary solution which is subsequently refined by a second optimization stage utilizing full-wave simulations. Specifically, the optimization targets a 1-bit coding scheme, where meta-atoms switch between two distinct states with a phase difference of 180 ± 37°. This hybrid approach demonstrates optimal convergence, reducing computational time by 25% compared to traditional full-wave-only techniques. Furthermore, a novel ``spiralling cross'' unit cell topology is introduced. Owing to its delay-line geometry, this structure provides additional degrees of freedom for spectral tuning and supports intermediate phase shifts, thus enabling encoding schemes beyond traditional 1-bit configurations. Experimental results confirm the validity of the proposed approach, demonstrating how the combination of versatile geometry and hybrid optimization effectively overcomes the trade-offs between numerical accuracy and computational efficiency.

A high-performance Two-Dimensional Photonic Crystal (2DPC) demultiplexer is proposed for application in Dense Wavelength Division Multiplexing (DWDM). Simultaneous high-field confinement and higher modal coupling are achieved using a new hybrid cavity geometry design, which consists of a square cavity with an inner rod radius (r = 110 nm) and a circular cavity with an outer rod radius (r = 100 nm). It is an operating silicon platform featuring a square lattice, bus waveguide, and four drop ports. Plane Wave Expansion (PWE) and Finite Difference Time Domain (FDTD) simulation methods reveal a large photonic bandgap (0.27-0.37a/λ) and excellent spectral performance, including a 98.75% average transmission efficiency, a high Q-factor of 7281, and precise 0.8 nm channel separation. System-level verification, Lumerical INTERCONNECT, and eye diagram and BER analyses were used to test signal integrity. The hybrid geometry also has a smaller footprint and improved integration, making it a suitable design for next-generation optical communication systems.

This study addresses an issue with high-energy laser directed energy weapon performance assessment when applied to the problem of countering swarms of uncrewed aerial systems (UAS). Queueing theory provides a suitable modelling framework for the performance assessment of such systems, as a single server queue can process only one threat at a time, based on the order in which threats arrive at the theatre of operation. Consequently, this introduces delays into the processing of sequences of threats. Delays in such queues typically have time-dependent service times, due to the target's movement. This results in considerable complexity in terms of producing performance predictions through stochastic models. In recent applications of queueing theory to directed energy systems an ad hoc approximation has been used to estimate the delays that threats experience while waiting for service. This approach involves approximating the processing delay of a given threat by a constant value. In particular, it has been estimated by measuring the delay as a product of the expected service time and the number of threats present less one. Such an approximation can result in severely reduced and inaccurate performance predictions. In the current study, the mean delay will be used instead, and improvement on the aforementioned approximation will be demonstrated through explicit examples of swarm UAS defeat.