A compact four-port circularly polarized multiple-input multiple-output (CP-MIMO) antenna with a dual-layer architecture is proposed for low-altitude communication. 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 was fabricated on two FR-4 substrates with an overall size of 0.85 lambda & times; 0.85 lambda & times; 0.084 lambda. In the lower layer, a dual-polarized feed backplane (DPFB) forms a +/- 45 degrees 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 extended the impedance bandwidth by 36%, from 7.55 to 10.08 GHz, and enabled LHCP radiation with a 3 dB axial ratio bandwidth of 8.22-8.89 GHz. A gain enhancement of 48% was also achieved. The measured results verified the design and demonstrated good MIMO diversity performance.
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.
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 2 wt%, 5 wt%, and 8 wt% 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.
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.
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 (0.27-0.37 a/lambda) 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.
In this study, a single-layer substrate and via-free transmit-reflect-array antenna based on a metasurface is proposed. The array antenna comprises transmissive and reflective unit cells arranged alternately in sequence. To achieve a 360 degrees phase coverage, two sets of antisymmetric U-shaped lines were etched on the top and bottom layers of the substrate to form the transmissive unit cells, and multi-layer stacking and vias are avoided. Moreover, by adjusting the lengths of a split-ring structure with phase delay lines for reflective unit cells, a 360 degrees phase coverage was achieved. The measurement results demonstrated that the antenna simultaneously generates a reflective focused beam with a peak gain of 20.8 dBi and a transmissive +1-mode OAM vortex beam with a peak gain of 20 dBi and a mode purity of 90 % at 17 GHz.
Megahertz wireless power transfer (MHz-WPT) enables compact resonant components; yet the matching, compensation, and filtering stages used in conventional systems can dominate loss and standby dissipation at MHz operation. To address this issue, this work proposes a compact 13.56 MHz WPT architecture in which impedance transformation is integrated into the resonant hardware. A self-resonant transmitting coil is co-designed with a Class-E power amplifier to shape the reflected load toward the optimum operating condition, thereby removing the external compensation network, additional matching stage, and lumped-element LC output filter. The analysis shows that, when the receiver is removed, the effective load becomes dominated by the transmitter resistance, inherently suppressing delivered power without sensing or closed-loop control. A prototype delivers 9 W over 30 mm with 81.5% end-to-end DC-DC efficiency, while under receiver absence, the DC input power decreases from 11 W to 1.15 W. These results demonstrate a simplified and robust MHz-WPT architecture with reduced component count and inherently low standby dissipation.
The curvature effects of curved metasurface (MTS) lead to oblique incidence and different unit radiation normal vectors (DURNVs). Oblique incidence causes a reduction in scattering amplitude and degrades focusing efficiency (FE), and DURNV distorts the radiation pattern of curved MTSs. To the knowledge of the authors, for the first time, this paper proposes a phase amplitude modulation and phase modulation (PAM-PM) combined modulation technique for cylindrical MTS to generate a high signal-to-noise ratio (SNR) and high FE three-dimensional (3D) shaped near field with a spiral cross-sectional shape. In addition, a near field with controllable spatial positions is a practical application requirement, and this paper provides a method to establish a 3D-shaped near field with controlled spatial positions. The proposed cylindrical MTS with PAM-PM modulation technique outperforms the PM technique significantly, achieving an SNR above 13 dB and an FE of 38.1%. For cylindrical MTS with only PM, there exists some noise, and the FE is 33.2%. This proposed modulation technique can be applied to 3D near-field systems based on conformal MTS, including wireless power transfer, radiometric temperature sensors for hyperthermia, and medical imaging systems.
In this work, a Substrate-Integrated Waveguide (SIW) cavity-based positive-feedback oscillator integrated with a slot antenna on a single substrate was designed. The proposed design incorporates a radiating element, an oscillator tank, and a coupling structure within the same cavity, thereby eliminating external interconnections and significantly enhancing overall efficiency. By employing the TE210 mode instead of TE110, the design exploits a field node to minimize the parasitic loading effects of the oscillator coupling probe on the antenna radiation. This approach simultaneously enhances the cavity's quality factor Q and preserves the spectral purity of the integrated SIW antenna-oscillator, all this without affecting the antenna radiation. The SIW cavity achieves a measured quality factor Q of 250, ensuring high spectral selectivity at the 10 GHz resonant frequency. The oscillator exhibits low phase noise of-131, dBc/Hz at a 1 MHz offset, along with exceptional suppression of harmonics, including the total suppression of the third harmonic, while the slot antenna achieves a gain of 6 dBi. This fully integrated architecture delivers performance equivalent to discrete implementations while offering a compact footprint and eliminating insertion losses between the antenna and the oscillator.
This letter presents a high-selectivity three-dimensional (3-D) dual-polarized frequency-selective rasorber (FSR). The proposed design comprises a 3-D array of multiple lossy strip-type resonators integrated with a planar bandpass frequency-selective surface (FSS). While the multiple resonances of the strips provide wideband absorption, a parallel LC structure is loaded within each resonator to achieve a low-loss transmission band. Numerical and experimental results demonstrate an ultra-wide low-reflection band with a fractional bandwidth (FBW) of 162.2% from 2.0 to 19.2 GHz. This includes a transmission band at 10 GHz with an insertion loss of 0.47 dB, alongside a lower frequency absorption band (2.0-9.5 GHz, FBW 130.4%) and an upper frequency absorption band (10.5-19.2 GHz, FBW 58.6%). The operating mechanism is further validated by an equivalent circuit model and measurement of a fabricated prototype, showing good agreement between theory and experiment.
Wide-stopband plasmonic filters are critical components for the development of compact mid-infrared (MIR) photonic systems. In this study, we propose a geometrically tunable wide-stopband plasmonic filter based on a meta-insulator-metal (MIM) waveguide integrated with dual resonator cavities. The optical response of the proposed structure is numerically investigated using the twodimensional finite-difference time-domain (2D-FDTD) method. We systematically analyze the influence of key geometric parameters, specifically the resonator height (H2) and inter-cavity distance (D), on the stopband characteristics. Our results demonstrate that the symmetric dual-cavity configuration provides effective control over both the stopband bandwidth and central wavelength. Consequently, the proposed design achieves a significantly broadened stopband while preserving structural compactness and high transmission selectivity, making it a highly promising candidate for integration into advanced MIR photonic circuits and sensing systems.
This letter presents a compact, low-profile single-substrate transmissive linear-to-circular polarization (LCP) converter designed and experimentally validated for point-to-point THz communication bands. The proposed LCP converter consists of an H-shaped gold metallic pattern deposited on both sides of a 100 & micro;m-thick fused silica substrate. The LCP converter operates within the 0.225-0.307 THz frequency band, achieving a simulated 3-dB axial ratio bandwidth of 30.8% in simulation. Owing to its wide axial ratio bandwidth, the proposed design is a promising candidate for point-to-point THz communication applications. The performance of the proposed converter is verified through surface current distribution, which explains the occurrence of Hyugen's response and equivalent circuit model. The proposed converter exhibits a measured 3-dB axial-ratio bandwidth of 27.8% in the frequency band 0.229-0.303 THz. The simple geometry and single-substrate implementation, with a thin profile and wide 3-dB axial ratio bandwidth, make the proposed design suitable for practical deployment scenarios.
Radar-based vital sensing methods have received significant attention due to their potential to provide continuous, noncontact measurements for heartbeat and respiration monitoring. Our original two-wave model extracts respiration and heartbeat data by formulating the estimation process as a minimization problem. Although the original method examines temporal changes in respiration and heartbeat signals in a different manner from existing methods, it remains sensitive to the slight body movements that often occur in laboratory experiments. In this study, we propose a modified two-wave model with improved robustness against such movements. Using experimental data collected with a millimeter-wave Multi-Input Multi-Output (MIMO) frequency-modulated continuous-wave (FM-CW) radar system, we demonstrate that the improved model can successfully measure both respiration and heartbeat signals even in cases where the original method fails, thereby improving the capability for non-contact vital signal detection.
In this letter, a frequency and linear-polarization (LP) reconfigurable antenna is proposed. The antenna consists of two pairs of printed dipoles as the primary radiating patches. By independently controlling the direction of the flowing current using loaded PIN diodes, the dynamic reconfiguration of both frequency and linear polarization can be realized. In addition, a dual-band artificial magnetic conductor (AMC) reflector is added under the radiator, which can effectively reduce the antenna profile to 0.1 lambda 0 (12.4 mm, where lambda 0 is the wavelength at low operating frequency). Both simulated and experimental results show that the proposed antenna can operate in four modes: 0 degrees LP low-frequency (2.36-2.77 GHz) state, 0 degrees LP high-frequency (3.25-3.68 GHz) state, 90 degrees LP low-frequency state, and 90 degrees LP high-frequency state. The antenna exhibits stable radiation patterns, with gain values of 7.56 dBi in the low-frequency state and 8.03 dBi in the high-frequency state. This antenna is suitable for ISM band applications, such as Wi-Fi (2.4-2.48 GHz) and Bluetooth (2.4-2.48 GHz), as well as TDD Band 42, meeting the requirements of modern wireless communication systems.
This study proposes a two-element Vivaldi antenna array that achieves broadband mutual coupling suppression and gain enhancement. First, by etching multiple spoof surface plasmon polariton (SSPP) slots on the ground plane to suppress surface-wave coupling, the inter-element isolation has increased from 20-31 dB to 20-45 dB, with an improvement of 5-10 dB (a peak of 20 dB) within the operating band of 1.8-4.5 GHz. Then, a quasi-transparent metasurface (MS) is placed above the aperture to enable phase compensation, converting spherical wavefronts to quasi-planar ones and thereby improving the gain of 0.5-2 dBi across the operating band. Finally, the designed Vivaldi antenna array is fabricated and measured, which exhibits S-11 < -10 dB (1.3-4.5 GHz), enhanced isolation, and stable gain performance.
Supplying battery-free power to wireless sensor systems (WSSs) mounted on rotating shafts remains a major challenge due to limited installation space, low rotational speed, and the requirement for long-term autonomous operation. This paper presents a compact dual-rotor energy harvester (EH) based on multilayer printed circuit board (PCB) sheets, designed for powering WSSs installed on ship propulsion shafts. Stacked multilayer PCB coils forming a three-dimensional structure are arranged on both the inner and outer rotors to enhance magnetic flux linkage and power density. The experimental results show that the EH generates power levels up to 959 mW at a shaft speed of 300 rpm. The output power improved nonlinearly with increasing rotational speed, demonstrating its suitability for real-time monitoring applications. The proposed EH offers a promising solution for powering WSS in autonomous driving technologies, with the potential for further optimization and integration into various mobility systems.
This study proposes an independently controlled polarization rotator with transmissive and reflective capabilities operating in two different frequency bands. The proposed independently controlled transmissive and reflective polarization rotator (ICTR-PR) unit cell consists of four metal layers separated by three substrates. The transmissive polarization rotator mode is realized by two strips (receiving strips) on the top layer, which are connected with two vias through circular holes inside the ground plane to two 90 degrees rotated strips (transmitting strips) on the bottom layer. The reflective polarization rotator mode was produced by connecting another pair of strips on the top layer to a microstrip line located in the middle layer. Properly adjusting the length of each strip allows both transmissive and reflective features to be independently controlled. The proposed rotator exhibits dual-frequency band resonances at 7.7 and 9.48 GHz for reflection and transmission responses, respectively. Furthermore, a high polarization conversion ratio (PCR) of more than 80% was achieved for both modes. A prototype was fabricated and measured to validate the simulation results. A good agreement between the experimental and simulated results was obtained.
