An all-in-one UHF RFID tag antenna using nonuniform meandered lines for retail garments in the textile industry is presented. The all-in-one antenna offers relatively low cost, wide band, compactness, and good conjugate matching in the presence of its robust housing with good dipole-like read range. Results show an antenna with a wide bandwidth of 900MHz and a long read range of 10.2 m making the UHF RFID tag antenna using nonuniform meandered lines a potential candidate for retail garments in the textile industry. Simulations are corroborated by measurements and are in fair agreement.

In this paper, the performance analysis of a reconfigurable intelligent surface (RIS) assisted underwater optical communication (UWOC) system with a decode-and-forward (DF) relaying protocol is presented. The radio frequency (RF)-RIS link is subjected to Rayleigh fading while the optical UWOC link experiences mixture Exponential-Gamma distributions subject to heterodyne detection and intensity modulation with direct detection (IMDD). In order to obtain a traceable closed-form expression, the statistical distribution of the RF-RIS link is derived in terms of Meijer-G function. Thus, the exact closed-form expressions for system end-to-end outage probability and average bit error rate (ABER) for different modulation schemes are then derived. To gain further insight about the derived analytical expressions, asymptotic expressions for the system are derived at high signal-to-noise ratio (SNR) through which the diversity gain is obtained. The findings show the significant impact of the number of RIS elements, detection technique, and the UWOC optical turbulence on the system performance. Finally, Monte-Carlo simulation is used to justify the accuracy of the derived analytical results.

A novel two-step synthesis method of sparse nonuniform-amplitude concentric ring arrays (SNACRAs) to maximize the beam collection efficiency (BCE) for microwave power transmission (MPT) is proposed in this paper. In the first step, beetle antennae search (BAS) algorithm is used to optimize the radius of each ring of the SNACRA, to obtain the maximum BCE and the equivalent continuous excitation of each ring. In the second step, we find the least array element on each ring to discretize the continuous excitation on each ring by using the binary search (BS) algorithm directly under the restriction conditions and then find the excitation of each element. Through the above two steps of optimization, the optimal synthesized parameters of the SNACRA, including the maximum BCE, layout, excitation and power pattern, can be obtained highly efficiently. Many representative numerical results under different ring numbers, apertures, and receiving areas are presented. Comparing these numerical results with those of other three arrays for MPT, it is proved that the SNACRA synthesized by the two-step method can get higher BCE with less elements and have a relatively simple feed network.

A novel class of dual-mode filters with improved high frequency sideband suppression response making use of coplanar waveguide (CPW) square loop resonator is presented. The resonator is placed on the bottom plane and inside the defected area of the ground. The resonant property of the CPW square loop resonator as well as the coupling property between two degenerate modes with different patch perturbation is studied in the paper. Two T-shaped orthogonal feed lines are arranged on the top plane, which not only provide proper excitation to the resonator, but also introduce an additional source-load coupling, so the proposed filter is found to have two transmission zeros at high frequency sideband and takes on asymmetric frequency response. Such a compact dual-mode CPW square loop resonator filter operating at 2.68 GHz is designed and fabricated.

A methodology for designing planar spiral antennas with a feeding network embedded within a dielectric is presented. To avoid a purely academic work which may not be manufactured with available standard technologies, the approach takes into account manufacturing process requirements by choice of used materials in the simulation. General design rules are provided. They encompass amongst others, selection criteria for dielectric material, aspects to consider when sketching the radiating element design, as well as those for the implementation of the feeding network. A rule of thumb, which may be helpful in the determination of the antenna supporting substrate's height, has been found. The appeal of the method resides in the fact that it eases up the design process and helps to minimize errors, saving time and money. The approach also enables the design of compact and small-size spiral antenna as antenna-in-package (AiP), and provides the opportunity to assemble the antenna with other RF components/systems on the same layer stack or on the same integration platform.

In this paper, a novel miniaturized frequency selective surface (MFSS) with capacitive loading is proposed; it has characteristics of low profile, second-order, wide-band, and remarkable wide stop-band properties. In a specific frequency band, the proposed MFSS has a second-order filter function characteristic. The proposed MFSS is composed of three metallic layers separated by two dielectric substrates, which offers the spatial form of the second order microwave filter. The band and operating frequency can be controlled by the thickness of dielectric substrates and the gaps between the capacitive loading structures. The element size is smaller than 0.05λ x 0.05λ. The element thickness is less than λ/30, where λ is the free space wavelength at the resonant frequency. The frequency response produced by the proposed MFSS had very good stability when the plane wave incidence angles varied from 0 to 60 degrees. The fundamental frequency f₀ is 2.45 GHz; the relative bandwidth δ is 10%; and the stop-band is from 3 GHz to 39.6 GHz. The frequency response demonstrates the excellent filtering performance.

This paper presents a new saw-tooth shaped sequentially rotated fractal boundary (SRBF) square microstrip patch antenna (SMPA) for wireless application. The square shape is rotated by an angle `θ' and superimposed, realizing fractal like geometry at boundary. The rotation of square shaped patch is divided in equal number of scaling angles θ_n such that for every iteration of angle θ, fractal boundary geometry has been realized. The square shape is modified into a circular shape patch resonating at 2.5 GHz. A 450 tilted rectangular slot is cut inside the radiating element to achieve circular polarization at 2.45 GHz. The antenna is fabricated using an RT Duroid 5880 substrate, having size of 70 mm x 70 mm. The antenna offers measured impedance bandwidth (VSWR < 2) of 50 MHz (2%) with simulated peak gain about 7 dBi. The fabricated antenna is tested, and measured results are in close agreement with simulated ones.

A novel CPW-fed circular polarized slot printed monopole antenna for 5G application is presented. The proposed slot monopole antenna occupies a small area of 0.23λ_o x 0.35λ_o x 0.019λ_o, and the wavelength has been obtained for the center frequency of 3.4 GHz to 3.8 GHz range. First, two square slots are inserted on either side of the feed line and to provide two orthogonal electric fields, a spiral stub is embedded in one of the slots. In order to improve the axial ratio bandwidth of the proposed antenna, it is possible to etch another spiral stub on the other side of the feed line. The proposed antenna provides circular polarized radiation such that the reflection coefficient bandwidth (below -10 dB) is about 1.4 GHz (from 2.9 GHz to 4.3 GHz) or 38.89%, and the axial ratio bandwidth below 3 dB is about 400 MHz, from 3.4 GHz to 3.8 GHz. This is 11.1% at center frequency of 3.6 GHz. This antenna covers the useful frequency bandwidth for 5G application. Simulation and measurement results are presented.

According to the orthogonality of each sub-carrier in the multi-carrier phase-coded (MCPC) signal, this paper focuses on anti-interrupted sampling repeater jamming (ISRJ) and creatively proposes a novel radar signal based on time-frequency random coded (TFRC) method, namely TFRC-MCPC signal. Based on the perspective of waveform design, the TFRC-MCPC signal adopts a chaotic sequence with good pseudo-random to code each chip in time-domain and each subcarrier in frequency-domain. The TFRC method increases the pseudo-randomness of radar waveform pulses and reduces the correlation between radar echo and ISRJ, thereby effectively suppressing the interference of false targets. The TFRC-MCPC method and common filter design methods do not conflict with each other and can be used in combination. The simulation experiment results show that under the typical parameters described in the paper, compared with the traditional MCPC signal and LFM signal, the signal-jamming ratio (SJR) improvement factor of the TFRC-MCPC signal is optimized by 1-2dB after pulse compression, which verifies its feasibility and effectiveness.

The present work describes a new wideband circularly polarized MIMO rectangular antenna in cube form for X-band application (8 to 11.8 GHz). Proposed antenna structure shows pattern diversity in whole 360° angle with polarization diversity. The isolation between the antennas is more than -14.5 dB. The impedance matching bandwidth (IMBW) is 3.8 GHz, and 3 dB axial ratio bandwidth is 2.91 GHz. The envelope correlation coefficient is less than 0.035, and its diversity gain is 10 dB. A copper metallic cylinder is placed inside the cube antenna to reduce the mutual coupling between the antennas.

This research work introduces a compact dual composite right/left handed (D-CRLH) unit cell structure for filtering power divider (FPD) application. The D-CRLH unit-cell consists of an interdigital capacitor with two shorted fingers in series. It contains a meander line, a rectangular stub, and a via in shunt, both series and shunt elements provide filtering response as a bandpass filter. This design has been developed on dielectric material of thickness 1.6 mm, usually called as Epoxy glass substrate (FR-4). The transmission line of length λ_g/4 of a Wilkinson power divider has been replaced with a D-CRLH unit cell to reduce the size of proposed structure more than 60%. Another advantage of using a D-CRLH structure is the position of resonance frequency independently controlled by series parameter only because of shorted structure. The series chip resistor has been utilized to improve the isolation at resonance in between output ports. It offers miniaturization with electrical footprint area of 0.15λ_g x 0.27λ_g (11.4 mm x 20.4 mm), here λ_g represents the guided wavelength at resonance frequency of 2.5 GHz.

The multilevel fast physical optics (MLFPO) is proposed to accelerate the computation of the fields scattered from electrically large coated scatterers. This method is based on the quadratic patch subdivision and the multilevel technology. First, the quadratic patches are employed rather than the planar patches to discretize the considered scatterer. Hence, the number of the contributing patches is cut dramatically, thus making the workload of the MLFPO method much lower than that of the traditional Gordon's method. Next, the multilevel technology is introduced in this work to avoid calculating the physical optics scattered fields from the considered scatterer directly, so that the proposed algorithm can significantly reduce the computational complexity. Finally, numerical results have demonstrated the accuracy and efficiency of the MLFPO method based on the quadratic patches.

It becomes more and more challenging to satisfy the long-term demand of transmission capacity in wireless networks if we limit our research within the frame of traditional electromagnetic wave characteristics (e.g., frequency, amplitude, phase and polarization). The potential of orbital angular momentum (OAM) for unleashing new capacity in the severely congested spectrum of commercial communication systems is generating great interest in wireless communication field. The OAM vortex wave/beam has different topological charges, which are orthogonal to each other. It provides a new way for multiplexing in wireless communications. Electromagnetic wave or synthetic beam carrying OAM has a spiral wavefront phase structure, which may provide a new degree of freedom or better orthogonality in spatial domain. In this paper, we introduce the fundamental theory of OAM. Then, OAM generation and reception methods are equally demonstrated. Furthermore, we present the latest development of OAM in wireless communication. We further discuss the controversial topic ``whether OAM provides a new degree of freedom'' and illustrate our views on the relationship between OAM and MIMO. Finally, we suggest some open research directions of OAM.

A new metasurface (MS) structure for wideband low radar cross section (RCS) and its performance as an antenna has been analyzed and proposed in this paper. The MS has been designed with two different AMC unit cells, and the novel AMCs scatter the incident waves diffusively. The parameters and dimensions of the AMCs are optimized to get the best performance of the antenna. Furthermore, the unit cell structure of metasurface is designed and positioned to improve the directivity of the antenna. The reflected electromagnetic waves scatter in a manner of 180⁰ out of phase with the incident waves, and the antenna's scattering and radiation performance has also been examined. Full-wave simulations and measurements confirm that the proposed antenna achieves 10 dB RCS reduction over a wide bandwidth of 3-12 GHz (61.2%). A monostatic peak RCS reduction of 45 dB is accomplished at 5 GHz, 7 GHz, and 11.5 GHz. Besides, the radiation characteristics of the antenna are appropriate in the boresight direction, and the antenna exhibits good performance in $E$-, $H$-planes and ensures adequate directivity.

In the iterative solution of the matrix equation arising from the multilevel fast multipole algorithm (MLFMA), sparse approximate inverse (SAI) preconditioner is widely employed to improve convergence property. In this paper, based on the geometric information of nearby basis functions pairs and finer octree grouping scheme, a new sparse pattern selecting strategy for SAI is proposed to enhance robustness and efficiency. Compared to the conventional selecting strategies, the proposed strategy has only one variable parameter instructing the constructing time and memory usage, which is more user friendly. Numerical results show that the proposed strategy can make use of the non-zero entries of near-field matrix in MLFMA more effectively and elaborately without compromising the numerical accuracy and the natural parallelization of SAI.

This paper presents a novel compact printed antenna exploitable for Dedicated Short-Range Communication at 5.8 GHz. The design of the proposed device is based on the concentric arrangement of two contemporary fed patches operating with different modes. The resulting antenna exhibits a fan-beam pattern, with a wide lobe in one plane and narrow lobe in the plane perpendicular to the former, while retaining exceptionally small dimensions. The actual width of the beam makes the antenna suitable to cover a single road lane, as prescribed by the Intelligent Transportation System framework requirements. Furthermore, it natively operates in Circular Polarization, as prescribed by the ETSI EN 302 663 normative. Experimental validations demonstrate that the proposed antenna presents a Left-Hand gain of 4.1 dB at center frequency, with HPBW_x and HPBW_y equal to 160˚ and 45˚, respectively, showing good agreement with the simulations. This measured performance confirms that the device is adequate to cover a single road-lane, according to the European framework for Dedicated Short-Range Communication for traffic monitoring.

Magnetic materials are found naturally in certain terrestrial and extra-terrestrial geological settings and can influence subsurface mapping and fluid transport and content estimations. With the advent of magnetic nanoparticle research there is also the possibility that these will be inputted in the environment on purpose, as research and industrial applications, or inadvertently as contaminants. The presence of magnetic materials is usually not considered in electromagnetic response modeling of saturated or partially saturated porous materials. This is because relative magnetic permeability of most natural materials is close to one, and thus should not affect propagation velocity calculations. The objective of this study was to investigate the effect of magnetic mineral inclusions on the velocity of propagation of an electromagnetic signal on porous materials saturated with water and its influence on volumetric water content estimation. The effective relative dielectric permittivity and magnetic permeability terms were modeled using Maxwell-Garnett, Polder-van Santen, Lichtenecker and Looyenga effective medium approximation equations. Data from three nonmagnetic soils saturated with water to varying degrees was used for preliminary model evaluations. The effect of magnetic minerals was tested by mixing magnetic sand with quartz sand at different proportions and measuring propagation velocity under fully water saturated conditions using Time Domain Reflectometry (TDR). Propagation velocity decreased with increasing magnetic volume fraction, while the effect of increasing magnetic fraction on attenuation factor was not markedly distinct. Water content estimations using models not accounting for magnetic inclusion substantially overestimated volumetric water content in saturated porous media.

Scattering of homogeneous plane waves by a Perfect Electric Conductor half-plane in uniform rectilinear motion in a simple lossless medium is investigated using Wiener-Hopf Technique in the context of Hertzian Electrodynamics. The cases of motion being parallel and perpendicular to the plane are tackled separately. Restrictions on incidence angle vs. speed for the realization of scattering phenomena are investigated in each case. Parallel motion mode reveals the possibility of excitation of surface waves upon reflection, which also contribute to edge diffraction mechanism. Numerical results are illustrated and discussed for scattered fields. Comparative theoretical results for the solution of the same problem using Special Relativity Theory are provided and discussed.

A traditional magnetic resonant coupling wireless power transfer (MRC-WPT) system is highly sensitive to the distance between transmitting and receiving coils. The transfer performance deteriorates at short distance due to magnetic over-coupling and magnetic weak-coupling at long distance which also results in the decrease of power. In order to improve the power transfer ability, this paper presents an MRC-WPT system with a novel design of resonant loops. Unlike the conventional system in which the receiving coil is identical with the transmitting coil, the receiving coil in the proposed system is different from the transmitting coil in terms of distance between turns. Theoretical equivalent models are presented to investigate the impact of the mutual inductance on the transfer efficiency. Based on numerical simulation, it is found that relatively more uniform mutual inductance can be obtained with the proposed resonant loops. With the proposed MRC-WPT system, the results show that the power transfer ability at short and long distances is improved. The average transfer efficiency is enhanced about 10% compared with the conventional system. Furthermore, the sensitivity of the proposed MRC-WPT system to lateral and angular misalignments is studied and compared with the conventional system. An experimental prototype of the proposed MRC-WPT system is designed for validation. The results show that the performance of the proposed MRC-WPT system outperforms the conventional system without adding any complicated control circuits.

The loss of magnetic bearing in the process of operation will lead to the temperature rise of the bearing and affect its performance. A permanent magnet is used to provide bias magnetic flux for hybrid magnetic bearing, which can reduce the loss and temperature rise of the magnetic bearing. In this paper, the loss of radial 2-DOF hybrid magnetic bearing (HMB) is analyzed. On this basis, the 3D thermal analysis model of HMB is constructed by using ANSYS Workbench finite element software. The loss is introduced into the temperature field as a heat source, and the temperature distribution of magnetic bearing is calculated. Combined with the results of loss and temperature analysis, the structural parameters were optimized by using genetic particle swarm optimization algorithm (GAPSO). The results show that the loss and temperature rise of the optimized magnetic bearing are significantly reduced.