This paper presents a design methodology that significantly increases the peak power handling capability (PPHC) of microstrip filters. The PPHC is limited in microstrip technology by the corona effect: a physical phenomenon caused by the ionization of the air under the presence of strong electric fields around the planar circuit. Microstrip filters with a low electric field strength in the air increases the corona threshold level, resulting in high PPHC. Conventional stepped impedance (SI) filters, which consist of cascaded step-shaped elements, exhibit sharp discontinuities. These geometric edges amplify the electric field strength in the air, consequently reducing the corona threshold. Our research group has recently reported a new synthesis technique that introduces a smooth-profile (SP) conductor strip. This SP strip eliminates any sharp discontinuities and significantly reduces the strength of the electric field. This paper focuses on the examination of the high power performance of 7th-order SP and SI low-pass filters. The cut-off frequency (f_c) for both types of filters is set at 447.45 MHz, while the frequency for maximum stop-band rejection (f_o) is 1 GHz. The findings indicate that the SP filter shows a notable enhancement in peak power handling capability (PPHC), with gains of 2.48 dB and 4.80 dB observed at critical pressure and ambient pressure, respectively.

This paper presents a design of high-performance parallel-connected filters using the Chained filtering function. The filtering functions enable the placement of multiple return loss zeros at the same frequency, resulting in reduced sensitivity to fabrication tolerance and design complexity compared to traditional Chebyshev counterparts. To demonstrate the feasibility of this technique, a new filtering function (F_N) based on Chained filtering function is derived, and prototypes of fourth and sixth-degree Chained function filters in a parallel-connected topology are designed and fabricated. The overall size of the filters is 2.5 cm x 4 cm (fourth degree) and 2.5 cm x 5 cm (sixth degree). The measured insertion and return losses are 2.833 dB and 16.150 dB (fourth degree), and 2.674 dB and 18.074 dB (sixth degree). The achievable selectivity of the filters is 78.17 (fourth degree) and 89.68 (sixth degree). This design technique can serve as a useful tool for filter design engineers in terms of implementation.

The paper presents a ground radiation antenna (GradiAnt) based triple-band MIMO antenna with wideband characteristics for Wi-Fi 6E applications. The GradiAnt is a novel antenna element with a series combination of inductor and capacitor in the feed loop, and dual-band characteristics have been achieved by controlling the impedance level of the antenna. By introducing a parasitic resonator within the feed loop of GradiAnt, triple-band characteristic is achieved and significant bandwidth enhancement is realized, fully covering the Wi-Fi and Wi-Fi 6E operation bands. The resonator consists of a parasitic strip connected with the ground plane through an inductor. Two identical GradiAnts are symmetrically installed at the corners of the shorter edge of the 55 × 40 mm² sized ground plane for MIMO scenarios. A loop-type isolator is installed between the antenna elements to decouple the lower Wi-Fi band where the higher bands are self-isolated. The measured bands with reference to -6 dB are 2.36-2.63 GHz and 4.768 GHz. The isolation in the lower and higher bands is greater than 22 dB and 17.5 dB, respectively. The ECC is less than 0.03 in the lower band and 0.16 in the higher bands.

The advent of acoustically mediated magnetoelectric (ME) antennas offers a new idea for miniaturizing antennas. The ME antenna operates at mechanical resonant frequencies, so its dimension can be reduced by three orders of magnitude compared to an electric antenna counterpart. However, the poor directional radiation property of the reported magnetoelectric antennas, which is similar to an ideal magnetic dipole, limits the use of the ME antennas. In this paper, we propose a tapered slot magnetoelectric (TSME) antenna which is composited of PZT-5H and Metglas with dimensions of 50 mm × 30 mm × 0.596 mm and an operating frequency of around 30 kHz. Inspired by the structure of the slot-coupled antenna, the structure of the magnetostrictive layer of the ME antenna has been modified, and the front-back radiation difference in the near field has been improved by 7.9 dB compared to a normal ME antenna. The different operating principles between the TSME antenna and normal ME antennas have been analyzed and verified in the paper. In addition, we have successfully implemented amplitude modulation (AM) signals transmission using TSME antennas. This work provides new ideas for improving the radiation performance of ME antennas and lays the foundation for their practical application.

A pentagon shaped ultra-wideband (UWB) antenna with a high selective notch at wireless local area network (WLAN) band is presented. An inverted L-shaped stub is incorporated with a pentagon-shaped metallic patch fabricated on an FR4 substrate. Also, a partial ground plane with a slot has been used to achieve UWB operation. Two structures are embedded into a patch to realize a rectangular notch. An electromagnetic band gap (EBG) structure is placed on the opposite side of the patch, and a rectangular complementary split ring resonator(RCSRR) is embedded in the patch. With the coupling of two structures, their notch bands are adjusted to achieve a rectangular notch. The bandwidth, upper and lower frequencies of the notch can be adjusted by varying dimensions of RCSRR and EBG. The measured and simulated results show S₁₁ ≤ -10 dB for 3.1 GHz-12.5 GHz with a notch at the WLAN band from 5 GHz to 5.91 GHz. Also, the proposed design has a stable radiation pattern and gain with a peak value of 3.5 dB at 9.5 GHz and -6 dB at 5.1 GHz. The miniaturized size of the proposed design (21.5 mm × 27.5 mm × 1.6 mm) with ultra wide bandwidth makes it suitable for wireless applications.

Optical nano-antenna offers a new scheme for solar energy collection by breaking through the band-gap limitation of semiconductor materials. However, complex structure, low efficiency, and narrow bandwidth remain major issues. To address these problems, we propose a novel helical optical nano-antenna based on the bridge structure. The antenna structure consists of two coplanar Archimedes spiral arms and a base layer. We analyze the influence mechanism of structural factors on its radiation efficiency and polarization characteristics. Our results show that the antenna structure achieves a total radiation efficiency of 83.13% in the wide wavelength range of 400 to 1600 nm, which is significantly higher than that of the previously proposed dipole nano-antenna. For different linearly polarized incident waves, the antenna structure obtains the same order electric field at the spiral gap, which indicates that the antenna structure can fully consider the polarization characteristics of sunlight. It fundamentally solves the problem that the linearly polarized antenna can only receive half of the solar energy, improving the absorption efficiency.

The possibility of near-field passive 3-D imaging using the aperture synthesis technique is theoretically proven and highlights the opportunity for imaging the entire human body by an antenna receiving array that surrounds the body. In these scenarios there will be partial obscuration of some regions of the body, by other parts of the body. This results in some receivers in the array being able to measure emission from certain parts of the body, while others are obscured from a measurement. A model is presented which enables the eects of obscuration to be assessed for planar-like, cylindrical-like, and concave-like regions of the human body. The eect the obscuration has on the spatial resolution of the imager is evaluated by examining the 3-D point spread function, as determined by a near-field aperture synthesis imaging algorithm. It is shown that over many areas of the human body, the Abbe microscope resolution of λ/2 (5 mm@30 GHz) in a direction transverse to the human body surface is achievable, an attractive proposition for security screening. However, the spatial resolution in a direction normal to the human body surface is shown to be close to λ(10 mm@30 GHz). In regions of greater obscuration, such as in the armpits, the resolution may fall to λ(10 mm@ 30 GHz) and 5λ (50 mm@30 GHz) in the directions transverse and normal to the human body surface respectively. It is also shown by simulation using a human body solid model and the 3-D aperture synthesis imaging algorithm how the image quality changes with the number of receiving antennas.

Aiming at the unsatisfactory accuracy and speed of traditional parameter identification methods for permanent magnet synchronous motors (PMSM), a parameter identification method based on an improved hunter prey optimization (HPO) algorithm (Tent chaotic initialization and firefly algorithm HPO (TF-HPO)) was proposed. Using the Tent chaotic map, the initial individuals are evenly distributed to enrich their diversity, and the population position is updated using the firefly perturbation algorithm. Simulation and practical experiments show that compared with unmodified algorithm, the improved algorithm has faster convergence speed and higher recognition accuracy, and can effectively identify the parameters of the motor. On this basis, deadbeat predictive current control is implemented, effectively eliminating current static errors and improving the accuracy and stability of the current control system, and can effectively suppress motor torque ripple and current harmonics caused by parameter deviations.

This study presents a novel design for a dual-band antenna that is compact, efficient, and suitable for both WLAN and WiMAX applications. The antenna features a circular patch with a Hilbert fractal structure and a coplanar waveguide feed line, resulting in a compact size of 24x34x1.6 mm³. By utilizing a Hilbert fractal slot and defected ground structure, the antenna can operate in two frequency bands, 2.39-2.47 GHz and 3-6.32 GHz, providing coverage for the desired WiMAX and WLAN bands. The experimental results demonstrate acceptable gains and high efficiency at the resonant frequencies, along with omnidirectional radiation patterns in the H-plane and bidirectional patterns in the E-plane. Notably, this design offers a nearly 50% reduction in size compared to comparable antennas and higher gain, representing a significant contribution to the field of dual-band antenna design.

Attenuation caused by various weather conditions and atmospheric turbulence significantly reduces the performance and reliability of free space optics (FSO) link. This paper employs simulations to analyze the signal quality of the proposed FSO link under various climate conditions. The performance analysis and parametric evaluation of the proposed 25 Gbps DP-QPSK based CO-OFDM FSO link with and without the spatial diversity technique is carried out. Also, we have compared the proposed FSO link with the 16-QAM-based OFDM FSO link for the vivid atmospheric conditions. The simulation results are analyzed in terms of key performance metrics such as bit error rate (BER), signal-to-noise ratio (SNR), link distance, received power and reliability. The results show that the FSO link with spatial diversity is more effective towards mitigating the adverse effects of atmospheric attenuation and turbulence in comparison with FSO link without diversity and 16-QAM OFDM-based FSO link. In total, this results in lower BER, higher SNR, improved received power and increased reliable distance for practical FSO communication system.

In this paper, we propose a new physical model to accurately estimate the absorption characteristics in Metamaterial Perfect Absorbers (MPAs). The proposed model, relying on the reflection and refraction theory of microwaves, explains the physical mechanism of absorption and how unit-cell constitutive parameters can contribute to control the absorption characteristics. By considering Floquet modes (TE and TM) as two incident cross-polarized waves, analytical expressions have been established to estimate the absorption at normal and oblique incidences from the extracted constitutive parameters of the unit-cell. Analytical predictions are in excellent agreement with numerical results, proving the validity of our model. Furthermore, it can give an idea behind the absorption characteristics of MPA unit-cells without passing through full-wave simulation which usually takes time. Compared to previous works reported in the literature, the proposed method is efficient and does not require time-consuming tests and processing steps. Finally, analytical findings in this work hold for the general shapes of MPA resonators.

In this article, a 15 × 20 mm² arbitrary-shaped antenna is built. The same is extended to a 2 × 2 MIMO antenna with size 32 × 20 mm². It covers two bands. Band-1 covers 3-4.44 GHz, and band-2 covers 5.32-11.1 GHz. In this case, a circular neutralization structure is used to lessen the mutual coupling between the two ports. The ECC, DG, CCL, and radiation pattern are used to demonstrate how well the MIMO antenna performs. Also, it has been noted that there is good agreement between simulated and measured outcomes.

Microwave imaging radar systems are often required for the recognition of hidden objects at various job sites. Most existing imaging methods that these systems employ, such as beamforming, diffraction tomography, and compressed sensing, which operate on synthetic aperture radar, produce highly distorted radar images due to the limitation of the frequency range, size of the array, and attenuation during the propagation, and thereby become hard to interpret the description of the object. Several methods explored for the recognition of hidden objects are based on deep neural network models with millions of parameters and high computational costs that render them unusable in portable devices. Moreover, most methods have been evaluated on datasets of microwave radar images of hidden objects with the same relative permittivity, orientation, size, and position. In real-time scenarios, objects may not have similar relative permittivity, orientation, size, and position. Due to variation in the object's relative permittivity, orientation, size, and position, there will also be variation in the reflectivity. Consequently, it is hard to say if those algorithms will be robust in real-world conditions. This paper presents a novel shape-based approach for recognizing hidden objects which combines delay-and-sum beamforming with an artificial neural network. The merit of this proposed method is its ability to simultaneously recognize and reconstruct the object's actual shape from distorted microwave radar images irrespective of any variation in relative permittivity, orientation, size, and position of hidden object. The performance of the developed technique was tested on a dataset of microwave radar images of various hidden objects having different relative permittivities, sizes, orientations, and positions. The proposed method yielded an average reconstruction rate of 91.6%. The proposed method is appropriate for evaluating occluded objects such as utility infrastructure, assets, and weapons detection and interpretation, which have regular shapes and sizes of the cross-section at various construction, archaeological and forensic sites.

A dual-band metasurface antenna is designed consisting of three-layer metal patches and two-layer dielectric substrates. To facilitate the modal analysis of the metasurface, Characteristic Mode Analysis (CMA) is used to analyze the metasurface antenna with 4×4 rectangular patches, and the performance of the antenna is optimized based on the Modal Significance (MS) curves. In order to excite the current of different characteristic modes at certain frequencies, the symmetric resonant arms and cross-shaped impedance matching converters are used in the feeding structure. The measured results are consistent with the simulated values, and the designed antenna can yield the gains of 7.67 dBi at 3.5 GHz and 7.28 dBi at 4.9 GHz, which provides the potential applications in 5G and other wireless communications.

Powerline communication (PLC) noise is the main cause of reduced performance and reliability of the communication channel. The major source of these noise bursts, which distort and degrade the communication signal, is the arbitrary plugging in and unplugging of electric devices from the electrical network. It is therefore important to perform statistical modelling of the PLC noise characteristics to enable the development and optimisation of reliable PLC systems. This paper presents the Variational Bayesian (VB) Gaussian Mixture (GM) modelling of the amplitude distribution of the indoor broadband PLC noise. In the proposed model, a fully Bayesian treatment is employed where the parameters of the GM model are assumed to be random variables. Consequently, prior distributions over the parameters are introduced. The VB criterion is used to determine the optimal number of components where the Bayesian information criterion emerges as a limiting case. To find the parameters of the GM components, the variational-expectation maximisation algorithm is employed. Measurements from different indoor PLC environments are then used to validate the model. Thereafter, performance analysis is carried out, and the VB framework is compared to the Maximum Likelihood (ML) estimate method. It is observed that while the ML model performs better when the amplitude distribution contains multiple peaks, the VB framework offers high accuracy and good generalization to the measured data and is thus effective in modelling the amplitude distribution of the PLC noise.

In the present era of wireless communication networks, the key area of concern is always the need for faster data rates to meet the growing requirements. The 5G standards have the fortitude to bring about rapid data transfer speeds, instantaneous connectivity, large data capacities, and minimal latency. In this paper, a novel octal patch integrated with a bow-tie parasitic antenna element with full ground plane that incorporates a microstrip dual band antenna was proposed for 5G n257/n261/n259 and n260 band applications. This bow-tie parasitic antenna element integrated octal patch single and MIMO antenna structure was mounted on an RT Duriod 5880 (ε_r = 2.2, loss tangent = 0.0009) with dimensions of 7.5 x 9.9 x 0.9 mm³ and 7.5 x 19.8 x 0.9 mm³ (0.67λ x 1.75λ x 0.07λ, where λ is considered at the lowest operating tuned frequency). A decoupling element was precisely placed in the core of a two-element MIMO antenna to reduce the mutual coupling. This embedded antenna radiating structure resonated in dual bands ranging 26.69-29.55 GHz and 38.24-42.53 GHz with a center frequency of 28 GHz and 40.2 GHz, respectively. This achieves a bandwidth of 2.85 GHz (10.3%) and 4.29 GHz (10.75%) at the dual bands. The maximum gains were 7.9 dBi and 6.97 dBi, and greater than 92% efficiency was obtained over the dual-band. From the results extracted from the proposed antenna, it was found that the antenna is capable of covering the 5G NR n257/n261/n259 and n260 bands with significant bandwidth, gain, isolation, ECC, DG, TARC, Multiplexing Efficiency, CCL MEG, and radiation efficiency. Thus, the antenna can be considered a potential contender for 5G millimeter wave wireless communication systems.

This paper presents a new process for additive manufacturing of purely metallic antennas based on Fused Deposition Modeling (FDM), with a filament composed by a mix between rounded shape copper powders with particle size in the range from 20 to 80 μm embedded in a polymeric matrix, to accomplish the desired antenna shape, followed by a post-processing involving de-binding to remove the base polymer and a further sintering process for obtaining a purely metallic component. This new process is validated by means of a prototype antenna consisting on a modified tri-band cactus monopole that is manufactured and measured demonstrating results in accordance with standard and alternative additive manufacturing techniques reported in literature.

The demand for high data rate, good channel capacity, and reliability is always the primary area of concern in the modern era of wireless communication systems. The 5G standards have the fortitude to bring about rapid data transfer speeds, instantaneous connectivity, large data capacities, and minimal latency. In this paper, a novel quadrangular slotted defected ground structure (QSDGS) that incorporates a microstrip wide band antenna (WMA) was proposed for 5G n46/n47/n79 and n102 band applications. The DGS was represented on the ground plane by four rectangular looped slots. An inset feeding technique was employed on this slotted patch antenna. This DGS loaded patch antenna structure was mounted on an RT Duriod 5880 (ε_r = 2.2, loss tangent = 0.0009) with dimensions of 33 x 29 x 1.5 mm³ (0.44λ x 0.38λ x 0.02λ, where `λ' is calculated at lowest operating wavelength). This embedded antenna radiating structure resonated in a wide band ranging from 4.03 GHz to 6.32 GHz giving an impedance bandwidth of 2.3 GHz (50%), with a centre frequency of 4.44 GHz. The maximum gain was 4.7 dBi, and greater than 75% efficiency was obtained over the wide band. From the results extracted from the proposed antenna, it was found that the antenna was capable of covering the 5G NR n46/n47/n79 and n102 bands with significant bandwidth, gain, and efficiency. Thus, the antenna can be considered a potential contender for 5G mid-band wireless communication systems.

In this paper, we present a new numerical anisotropy optimization method for the three-dimensional (3D) radial point interpolation method (RPIM) in lossy media. Instead of evaluating the parameters of the artificial anisotropy or the scaling factors along the selected axes, as it is usually done in classical optimization algorithms, once the analytical expressions of these parameters have been determined, they are assigned at each node through their shape functions. By adaptive factor, we mean that its value varies in such a way to cancel the discrepancy between numerical and exact wavenumbers at each node. Doing such optimization at each node is indeed being possible during the calculation of these parameters by the RPIM dispersion relation. Therefore the numerical anisotropy is no longer optimized by averaging over the entire Cartesian grid but in each node direction. The RPIM numerical anisotropy adaptive optimization method (AOM) in lossy media is presented, and the theoretical adaptive factors are given as functions of nodes positions. Our results show that the numerical errors of the dispersion and the anisotropy are considerably reduced, after being optimized with the AOM. The proposed AOM scheme is applied for a 3D rectangular cavity in order to test its validity and evaluate the accuracy of the numerical results of our approach.

Two different MIMO antennas configurations are proposed in this paper for operation around 30 GHz with a bandwidth of 0.8 GHz. The proposed configurations are applicable in 5G, 6G and radar systems in Ka-band systems. Each of the proposed configurations consists of four identical rectangular elements where each element is connected to an impedance transformer for impedance mismatch improvement. Due to the close existence of antenna elements, mutual coupling can seriously degrade the gain, signal to noise ratio, matching characteristics, and efficiency of the MIMO antenna systems. To overcome performance degradation, several techniques such as Curved Edges (CE), Defected Ground Structure (DGS), and Band Gap Structure (BGS) are implemented. Simulation was carried out using the commercial Computer Simulation Technology (CST) and High Frequency Structure Simulation Software (HFSS). Prototypes are fabricated and measured. The experimental results show good agreement with the simulated ones. Improvement in the mutual coupling value from -21.4 dB to -27.2 dB also proves the practicality of this design.