A low-profile, dual-band, shared-aperture antenna with a large frequency ratio is presented, based on a meshed patch and an AMC-backed Fabry-Perot (F-P) cavity. By taking advantage of the weak frequency sensitivity of grid slotting in meshed patches, the upper meshed patch is utilized as both the parasitic patch for the low-frequency antenna and the partially reflective surface (PRS) for the high-frequency F-P cavity, thereby simplifying the overall structure. Meanwhile, the AMC ground is employed to control the reflection phase and reduce the cavity height to λ/4, which enables both antennas to share the same aperture within an 8-mm profile. A prototype is fabricated and tested at 1.6 GHz and 15.14-15.46 GHz. Measured results demonstrate a frequency ratio of 1:9.6, a peak gain of 6.2 dBi at 1.6 GHz, a peak gain of 11.8 dBi in the high-frequency band, and a port isolation better than 17 dB. The proposed antenna features compact size, low profile, and efficient structural reuse, making it attractive for integrated multi-band communication systems.

We present a review of homogenization models of microwave wire media with different geometries. We begin with a simple (uniaxial) wire medium and then consider more complex types of wire media - double, triple, and interlaced wire media - which remain underexplored. We discuss boundary problems with wire media and the most important physical effects revealed using the reviewed homogenization models.

This work presents deep neural networks for the inverse design of an ITO-film angular-selective metasurface absorber. A tandem deep neural network (T-DNN) framework is developed for the inverse design of electromagnetic metasurfaces. A forward network is first trained independently to learn the complex physical mapping between metasurface structures and their electromagnetic responses. An inverse network is then trained in tandem with the pre-trained forward network, eliminating conventional parameter-by-parameter tuning and establishing a performance-driven pipeline that directly maps target electromagnetic responses to structural parameters. Using the trained network, several metasurface absorbers with distinct angular sensitivities are rapidly designed, and their angle-dependent applications are preliminarily investigated. Results show that deep learning enables the fast design of metasurface absorbers customized to realistic incident angle distributions, yielding efficient omnidirectional radar cross-section (RCS) reduction at sensitive angles. This work offers a new strategy for the fast design of omnidirectional scattering suppression.

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 the 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.

This study presents a method which improves the accuracy of Preisach model that is able to reproduce the magnetic response of ferromagnetic material to change of magnetic fields, especially at higher frequency. The approach consists in extending an existing model and uses mathematical tools like combining a closed-form Everett function for hysteresis modeling with the Monte Carlo integration method to approximate the Preisach function, making calculations faster and more reliable. To find the best settings for the model, two optimization techniques are used: genetic algorithms (GA) and artificial bee colony (ABC). The model is tested by comparing its predictions to real-world experimental data, and it shows excellent accuracy and efficiency. Between the two techniques, GA performs better in terms of precision and reliability, making it a good choice for solving complex problems in modeling magnetic behavior.

Long-range wireless power transfer (WPT) is difficult with unguided radio waves or magnetic coupling. In this work, a plasma-assisted quasi-parallel planar waveguiding medium is proposed for overcoming the transmission range issues. Method: A dielectric layer sitting on a conductive object or grid was used as a medium for WPT. At the transmitting end, a plasma ball shielded with a spark-gap activated hemispheric metal cap was used to ionize the air in the space, thereby forming the top cladding layer of the quasi parallel-plate waveguide. At the receiving end, the transmitted power was coupled out of the waveguide over the entire ultrasonic spectrum using Avramenko diode configurations. A Kretschmann-like configuration was used at both ends for conversion between a plasmonic current and the surface waves. Results: In the proposed experimental setups, the transmitted power was successfully harvested over a frequency range from near DC to 230 MHz, with the ratio of the received power to the transmitted power significantly surpassing the value predicted by the Friis' two-ray ground reflection model. Conclusion: WPT based on surface waves is technically feasible with the help of Kretschmann-like configurations.

This research paper presents a low-profile ultra-wideband (UWB) multiple-input multiple-output (MIMO) antenna with enhanced isolation and wideband performance, employing polyimide as the substrate. The suggested configuration consists of two symmetric radiating elements incorporating rectangular and circular slots within a compact footprint of 36 × 21.1 × 0.1 mm³. To effectively suppress mutual coupling, a slot-based metamaterial-inspired defected ground structure (DGS) with a meandered profile is introduced between the antenna elements. In addition, inverted U-shaped stubs and optimally placed slots are integrated to form a stub-loaded decoupling network, further improving inter-element isolation across the UWB spectrum. The antenna exhibits resonant modes at 4.16 GHz (WLAN), 5.49 GHz (IoT and smart home applications), 7.54 GHz (satellite and point-to-point communications), and 11.61 GHz (high-resolution imaging and sensing), covering the 4-12 GHz frequency range. Predicted and tested outcomes present good agreement, with key MIMO performance parameters achieving Channel Capacity Loss (CCL) below 0.4 bits/s/Hz, diversity gain (DG) above 9.9 dB, Envelope Correlation Coefficient (ECC) below 0.005, and Total Active Reflection Coefficient (TARC) less than -10 dB. Owing to its compact size, wideband operation, and high isolation characteristics, the suggested antenna is a strong candidate for wireless area networks and emerging IoT-based sensing applications.

Wide-stopband plasmonic filters are essential components in compact mid-infrared (MIR) photonic systems. This work proposes a geometrically tunable wide-stopband plasmonic filter based on a metal-insulator-metal (MIM) waveguide with dual resonator cavities. The optical response is numerically investigated using the two-dimensional finite-difference time-domain (2D FDTD) method. The influence of the resonator height H₂ and the inter-cavity distance D on the stopband characteristics is analyzed. The symmetric dual-cavity configuration enables effective control of the stopband bandwidth and central wavelength. The design achieves a significantly broadened stopband while maintaining compactness and high transmission selectivity, making it a promising candidate for integration into mid-infrared photonic and sensing systems.

This letter presents a compact, low profile singe 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 μm-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 Huygens 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.

A circularly polarized (CP) millimeter-wave phased array antenna (PAA) is proposed for wide-angle scanning applications. The antenna is composed of radiating patches, coupling patches, and a ground plane. A single element consists of a centrally fed microstrip CP antenna with double arc-shaped slots, with a parasitic patch loaded on its top. A sequentially fed 2 × 2 subarray is constructed by arranging single elements in a specific orientation, and the central disc-ring structure is combined with the square ring patch structure based on the beam complementarity principle to broaden the beamwidth. Both simulations and measurements are performed on a 4 × 4 prototype array. The proposed antenna operates over a frequency band of 27.6-30.4 GHz, 3 dB AR bandwidth covers working bandwidth. When the beam scans to ±60°, the gain degradation relative to the boresight direction is only 1.1 dB, with the AR at the beam pointing angle maintained ≤3.5 dB. The proposed antenna boasts a compact size, facile fabrication process, and excellent wide-angle scanning capability, and it provides a novel design paradigm and practical solution for CP millimeter-wave wide-angle scanning PAA systems.

A novel integration method of a polarization conversion metasurface (PCM) and an array antenna for radar cross-section (RCS) reduction is presented. This method combines the PCM with a slot array antenna operating at 11.5 GHz for reducing RCS. The metasurface is composed of polarization conversion units arranged in a checkerboard pattern, and each PCM unit cell is made up of two symmetrical fork-shaped structures. The polarization conversion units can achieve a polarization conversion rate of over 90% in the frequency band of 10.12-19.93 GHz (65%). The measurements demonstrate that the antenna attains over 10 dB RCS reduction in the frequency range of 9.9-20.7 GHz (71%). Meanwhile, the radiation performance of the antenna is effectively preserved.

This study proposes a broadband, wide-angle metasurface for bistatic radar cross-section (RCS) reduction by integrating a low-profile bent-line unit design with an Adaptive Binary Particle Swarm Optimization algorithm enhanced by Array Pattern Synthesis (ABPSO-APS). The optimized metasurface achieves over 10 dB of bistatic RCS reduction across 8.4-21 GHz (86.7% fractional bandwidth), with a peak reduction of 22 dB, outperforming conventional checkerboard, genetic algorithm, and particle swarm optimization layouts by 22.82%, 15.27%, and 7.91%, respectively. The design also exhibits angular stability up to 30° and polarization insensitivity under both TE and TM incidences, while maintaining an ultrathin profile of only 0.1λ (where λ is the wavelength at the center frequency). These results demonstrate its strong potential as a compact and efficient solution for advanced electromagnetic stealth and radar signature control applications.

Supplying battery-free power to wireless sensor systems (WSS) 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.

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 flowing current using loaded PIN diodes, the dynamic reconfiguration of both frequency and linear polarization (LP) 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 0.1λ₀ (12.4 mm, where λ₀ is the wavelength at low operating frequency). Both simulated and experimental results show that the proposed antenna can operate in four modes: 0° LP low frequency (2.36-2.77 GHz) state, 0° LP high frequency (3.25-3.68 GHz) state, 90° LP low frequency state, and 90° 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 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° 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.

We present the design, fabrication, and experimental characterization of two 150 mm Luneburg lenses for X-band (10 GHz), produced by FFF using standard PLA. The printed PLA permittivity was measured with a 7 mm coaxial cell and EpsiMu, yielding ε_{r, PLA} ≈ 2.5 at 100% infill; a volume-weighted mixing model with perimeter correction was used to set discrete radial infill fractions. Two infill patterns (grid and gyroid) were tested, and waveguide mounts were integrated for reproducible alignment. Insertion-loss tests give 1.5 dB (grid) and 1.1 dB (gyroid) at 10 GHz. Far-field measurements (R = 1.5 m) and Friis-based estimates yield peak gains of 20.5 dBi (grid) and 19.4 dBi (gyroid) (simulation: 20.8 dBi); the waveguide reference gain is 4.9 dBi. Near-field tests at R = 0.15 m show an on-axis S₂₁ improvement of +2.33 dB, which corresponds to a low apparent near-field aperture efficiency (1.8-2.3%) while far-field efficiencies inferred from the measured gains are substantially higher (35-45%). These results confirm that discrete infill grading in low-cost FFF-printed PLA can realize effective Luneburg lenses at X-band, with quantifiable trade-offs among insertion loss, infill geometry, and realized aperture efficiency.

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 S₁₁ < -10 dB (1.3-4.5 GHz), enhanced isolation, and stable gain performance.

Radar-based vital sensing methods have received significant attention due to their potential to provide continuous, non-contact 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.

This study explores the anisotropic electromagnetic properties of carbon nanotube (CNT)/polylactic acid (PLA) nanocomposites, fabricated in-house and shaped using traditional compression molding and advanced 3D printing techniques. By examining the effects of CNT content (ranging over 1-4 wt.% (weight percent)) and 3D printing path orientation, this research investigates how these factors influence shielding effectiveness (SE) and the corresponding nanocomposite complex dielectric permittivity tensor. Notably, a significant variation in SE was observed between the different printing path orientations, with a difference of over 20 dB at 4 wt.% CNT. Experimental measurements were used to develop an anisotropic model for the complex dielectric permittivity, with the permittivity components for samples at 4 wt.% CNT extracted to be 36.5-j44.5 along the printing direction (ε_||) and 8.3-j3.1 in the perpendicular direction (ε_⊥) over the X-band frequency range (8.2-12.4 GHz). These findings demonstrate that CNT alignment during 3D printing induces highly directional electromagnetic properties. Furthermore, we demonstrate that anisotropic simulation models provide a more accurate prediction of the electromagnetic response of 3D-printed nanocomposite structures than isotropic models. In brief, this study emphasizes the necessity of considering anisotropic properties in the design and simulation of 3D-printed nanocomposites for electromagnetic shielding and other applications.