Owing to the principle of relativity, the present state of knowledge explicitly allows Maxwell's equations to be solved not only in the rest frame of an electromagnetic transmitter but also directly in the rest frame of the receiver without use of the Lorentz transformation and the Lorentz force. Recently, such a calculation was first performed for the Hertzian dipole. The analysis of the resulting formula breaks new scientific ground and indicates that Maxwell's equations predict that electromagnetic waves in vacuum propagate at the speed of light, notably for each receiver, even when these receivers have relative velocities with respect to each other. Although this paradoxical phenomenon was expected, the finding that Maxwell's equations nevertheless predict a classical Doppler effect was unexpected and indicates inconsistent or not yet fully understood aspects of canonical Lorentz-Einstein electrodynamics consisting of Maxwell's equations, Lorentz force and Lorentz transformation.

This study focuses on the utilization of a slotted patch MIMO antenna to enhance isolation and gain. The MIMO antenna configuration includes two radiators integrated with an array of Frequency Selective Surfaces (FSSs). These antenna components are implemented on an FR-4 substrate and encompassed by FSS units that are optimized for X-band frequencies. The proposed MIMO antenna possesses dimensions of 65 mm (width) × 45 mm (length) × 1.6 mm (height). The primary objective of incorporating FSSs is to not only enhance isolation but also achieve high gain. The proposed FSS design features a circular ring structure with a rectangular loop at its center. The FSS unit cells exhibit excellent stability across various polarization incidence angles and operate within the frequency range of 7 to 9 GHz. The FSS loaded antenna offers a bandwidth ranging from 8.0 to 8.55 GHz, with a peak gain of 6.5 dB and isolation exceeding -20 dB among the MIMO elements. Furthermore, the study explores the MIMO antenna's performance in terms of diversity gain (DG), efficiency, and Envelope Correlation Coefficient (ECC), demonstrating superior results compared to existing state-of-the-art approaches. The proposed findings are validated by fabricating a sample prototype and conducting a comprehensive comparison between simulated and measured results.

A novel wideband circularly polarized (CP) dipole antenna for RFID/WiMAX/WLAN applications is presented. A pair of crossed fan-shaped dipoles printed on both sides of the substrate are used as the primary radiating elements. The antenna achieves circular polarization by using a 90° phase shifted microstrip line between the dipoles. By changing the edge of fan dipoles into Minkowski fractal curve, miniaturization and wide bandwidth of the antenna can be realized. Besides, incorporating the U-slot into the fractal crossed dipoles can obtain a wider bandwidth. The test results show that the proposed antenna achieves a wide impedance bandwidth of 63.2% (1.9-3.7 GHz) for VSWR < 2 and a 3-dB axial ratio (AR) bandwidth of 42.9% (2.2-3.4 GHz). The maximum gain in the operating frequency band can reach 7 dBi. The proposed antenna has good radiation characteristics in both low and high frequencies, which makes it a candidate for applications of RFID, WLAN, WiMAX, and other communication systems.

Recently, the study of acoustic vortex beams has attracted a great attention owing to its potential applications in medical ultrasound imaging and trapping particles. In some special applications of medical ultrasound, it generally needs the simultaneous realization of vortex focusing and asymmetric propagation in three-dimensional (3D) space. However, the design of a two-dimensional (2D) device with asymmetric acoustic vortex focusing (AAVF) remains a challenge. To overcome it, we experimentally demonstrate a 2D AAVF lens composed of three types of binary-phase mode converters. By simultaneously introducing the phase profiles of acoustic focusing and vortex caused by the mode converters, we design a 2DAAVF lens with the topological charge n = 2, i.e., the sound energy can pass through the lens from the upper side and forms a vortex focus in 3D space; however, it cannot transmit through the lens from the other side. The vortex focusing and asymmetric transmission arise from the phase manipulation and the conversion between the zero-order and first-order waves caused by the mode converters, respectively. The measured fractional bandwidth can reach about 0.19. The proposed lens has the advantages of high-performance AAVF, broad bandwidth and complex sound modulation in 3D space, which provides diverse routes for designing 3D multi-functional sound devices with promising applications in medical ultrasound.

This research paper introduces a novel dual-band single-polarized (DBSP) series-fed center-fed open stub (SFCFOS) Binomial Antenna Array synthesis technique to improve side lobe levels (SLL) and better isolation for the use in Airborne Synthetic Aperture Radars (AIR-SARs). The antenna utilizes a shared-aperture array (SAA) architecture, operating in both X and Ku-bands with center frequencies of 9.3 and 13.265 GHz with a frequency ratio of 1:1.426. The SAA consists of a 7-element linear array of square microstrip patches for the X/Ku-band. The inter-element spacing between patches is set at 0.7λ to meet the ±25˚ scan range requirements. The X-band (9.3 GHz) frequency is ideal for soil moisture estimation in agricultural areas, while the Ku-band (13.265 GHz) is suitable for applications in snow-covered regions, cold areas, and disaster monitoring. To validate the antenna design, a prototype is fabricated and tested for S-parameters, radiation characteristics, and gain measurements. The size of the shared-aperture antenna is 200 mm × 50 mm × 0.787 mm. The measured results of the prototype align well with the simulated ones, exhibiting excellent radiation performance and high isolation. The bandwidth of 1.07% (X-band) and 1.5% (Ku-Band) and return loss of 25 dB/-15.7 dB at 9.3/13.265 GHz are achieved. The measured isolation is -45 dB which provides a large signal separation at X/Ku-bands. The antenna design shows a side-lobe level (SLL) of -39.5 dB at E-Plane (φ=0˚) and -17.9 dB for H-plane (φ=90˚) for the X-band and -35 dB at φ=0˚-19 dB for H-plane (φ=90˚) for the Ku-band. Additionally, it achieves high gain values of 12.8 dBi for the X-band and 13.2 dBi for the Ku-band. This research presents the first reported shared-aperture X/Ku-band single polarized planar array with binomial amplitude distribution synthesis technique, which holds significant value for AIR-SAR applications. All the measured results were in line with simulated ones and matched reasonably well.

This study presents a pioneering curved antenna design that is seamlessly integrated into Wireless Capsule Endoscopy (WCE) devices. The proposed antenna features a miniature height of 25 mm, a radius of curvature of only 5.5 mm, and a conductive line width of up to 2 mm, making it an ideal fit for use in compact WCE applications. The antenna is specifically designed to operate in the ISM5800 band and achieves outstanding performance metrics, such as an S₁₁ of -10 dB and a Gain of 5.8 dBi. To evaluate the safety of our design for human usage, we conducted an investigation of the specific absorption rate (SAR) of the Hugo Model antenna in various positions for ISM5800 and compared our findings to the safety limits specified by the Federal Communications Commission (FCC) standards. Our results confirm that the proposed antenna design meets the safety requirements for wireless communication systems in biomedical applications, thereby demonstrating its potential for clinical use.

A Koch Snowflake fractal structure embedded octagonal patch antenna with hexagonal split ring for Ultra-Wide Band (UWB) and 5G applications is proposed. In this proposed design, Koch Snowflake pattern is chosen for embedding into the octagon-shaped patch antenna, which tentatively develops a miniaturized cross-sectional area in the radiator and introduces wide resonance with enhanced gain. A hexagonal split ring is introduced into patch to handle negative refraction in the radiations and to initiates self-inductance and capacitance which manages the impedance matching. Here, a co-planar waveguide (CPW) is employed for transferring electric field into patch and a lumped port is used to induct field between patch and ground. The two slots S1 and S2 made on ground are supportive in obtaining wider resonance. The Substrate used in the proposed design is Flame Retardant 4 (FR-4), which is utilized in various electronic modules. The dielectric constant and loss tangent of FR-4 substrate are ε_r = 4.4 and δ = 0.02 respectively. The complete dimensions of the proposed model are 25 x 30 x 1.6 mm³. The simulated antenna is designed using Ansys High Frequency Electromagnetic Simulation Software 17.2 (HFSS 17.2). The simulated design features a Peak Gain of 6.3 dBi and Fractional Bandwidth (FBW) of 168% (Frequency ranges from 2.6 GHz to 28.9 GHz) with Bandwidth ratio of 11.1:1. Also, the designed antenna is fabricated using Milling method and the fabricated prototype offers Fractional Bandwidth (FBW) of 168% (Frequency ranges from 2.4 GHz to 28.5 GHz) and gain of 6.27 dB which are tested and measured using Microwave analyzer and anechoic chamber. Thus, the proposed antenna covers the resonance which includes S-band, C-band, X-band, Ku-band and K-band. Also, it completely wraps the UWB spectrum range (3.1 GHz to 10.6 GHz), 5G (Sub-6 GHz band) Frequency Range 1 (FR 1) spectrum, and most deployed 5G mm-wave Frequency Range 2 (FR2) spectrum (24.25 GHz to 29.5 GHz).

In the current system of wireless communication, Users expect devices that are lightweight and offer broad bandwidth as well as a high data transmission rate. Developments in data speeds, bandwidth, ultra-low response times, excellent dependability, considerable accessibility and improved device-to-device connectivity are what have driven wireless systems toward 5G. These 5G wireless systems require small and efficient antenna designs. This work proposes a 5G mm-wave quadrilateral slotted defected ground structure (QSDGS) including a wideband monopole antenna (WMA) for n259 and n260 5G mm-wave bands. Here, the DGS was modelled using two quadrilateral slots on a ground plane. An inset feeding technique and multiple slots were employed to patch. This structure consists of a DGS-loaded slotted antenna patch mounted on a Rogers/RT Duriod 5880 (ε_r = 2.2, loss tangent = 0.0009) with dimensions of 12x11x0.9 mm³ (1.42λ_gx1.30λ_gx0.10λ_g). This embedded antenna radiating structure resonates from 35.5 GHz to 44.7 GHz, giving an impedance bandwidth of 9.2 GHz (24.2%), with a centre frequency of 38 GHz. 9.48 dB was the peak gain, and 83-94% efficiency was obtained over the wide band. Based on the extracted data from the proposed antenna, it was found that the antenna is capable of covering the 5G NR n259 and n260 with significant gain, bandwidth, and efficiency. Thus, the antenna has the ability to be considered a possible contender to be used in 5G wireless applications using mm-wave frequencies. A good agreement can be seen here between simulated and measured return losses.

Enhancing the capacity of wireless communications systems is necessary to manage growing networks. Thus, this work presents an analytical model for describing the deterioration in orbital angular momentum (OAM). The proposed model is based on a uniform circular array, which can be applied in OAM generation to obtain the desired beam properties. First, the side-lobe problem in OAM applications is examined and resolved by optimizing the beam synthetization. Then, comparisons between the two window techniques are used to evaluate their impacts. Finally, the effects of selecting the optimal window technique and width on the solutions are investigated. Numerical results and the comparisons between derived formulas and those obtained via full-wave numerical simulations are shown.

This letter presents a compact constant absolute bandwidth (ABW) frequency tunable bandpass filter (BPF) with bandwidth and tuning range enhancement. The fundamental structure consists of two varactor-loaded step-impedance resonators (SIRs) and input/output feeding lines. By adjusting the position of varactors, the slope of coupling coefficient between the two resonators can bechanged easily, which is crucial to realizing constant ABW. The tuning range is improved due to the application of varactor-loaded SIR. To expand the bandwidth, interdigital coupling structures between varactor-loaded SIRs are adopted. Besides, source-load coupling is introduced, and two transmission zeroes (TZs) are generated on both sides of the passband to enhance the rejection level of stopband. The measured results show that the proposed BPF achieves a center frequency tuning range from 0.79 to 1.2 GHz (41.2%), and the 3-dB ABW remains 108 ± 5 MHz. The insertion loss (IL) is 1.8-2.2 dB, and the return loss is greater than 10 dB during the whole tuning range.

This paper presents the design, fabrication, and measurement results of a flexible folded dipole rectenna for 5G technology. The proposed rectenna is a single-sided structure fabricated on a flexible Kapton substrate with a maximum RF to DC conversion efficiency close to 53% for an input power of -9 dBm at 3.5 GHz with 3-KΩ. Moreover, the measured results show that the conversion efficiency is above 40% across a broad range of input power levels (from -14 to -8 dBm). The paper discusses the prototype's design and simulation results, fabrication steps, and measurement results. The proposed rectenna is compact, low-cost, and flexible, making it suitable for wearable applications.

An efficient time domain hybrid method, consisting of the finite-difference time-domain (FDTD) method, Norton's theorem, transmission line (TL) equations, and some interpolation techniques, is presented to realize the fast coupling simulation of branched lines (BLs) radiated by ambient wave. Firstly, the branched lines are decomposed into multiple independent multi-conductor transmission lines (MTLs) according to the branched nodes. Then the TL equations with interpolation techniques are employed to build the coupling model of each MTL. The transient responses on these MTLs are solved by the FDTD method, which are employed to extract the Norton circuits of these MTLs acting on the branched nodes according to the Norton's theorem. Finally, the correlation matrix of the voltages and currents at the ports of the branched nodes is derived and solved. Meanwhile, these voltages are fed back to the corresponding MTLs as boundaries to realize the interference signal transmission among the BLs. Numerical examples about the coupling of branched lines contributed by five wires in free space and complex environment are simulated and compared with that of traditional FDTD to verify the correctness and efficiency of this proposed method.

At present, numerical methods suitable for the electromagnetic interference (EMI) analysis of the transmission line (TL) excited by the leakage electromagnetic (EM) fields generated by the integrated circuit (IC) of the electronic device are still rare. An efficient time domain hybrid method, consisting of the dynamic differential evolution (DDE) algorithm, transmission line equations, finite difference time domain (FDTD) method and non-uniform grid technique, is presented to realize the fast simulation of the leakage EM fields to the TL. Firstly, a source reconstruction method based on the DDE algorithm is employed to extract the equivalent dipole array to represent the leakage EM radiation from the IC of the device. Then, the coupling model of the TL excited by the leakage EM fields is constructed by the TL equations and non-uniform grid technique, and solved by the FDTD method to realize the synchronous calculation of the leakage EM field radiation and the transient responses on the TL. Finally, the correctness of the source reconstruction method has been tested, and the accuracy and efficiency of the proposed method have been verified via two simulation cases of the transmission line excited by leakage EM fields arising from IC in free space and shielded enclosure by comparing with that of the MOM method.

In plantation areas, soil conditions affect the crop's quality. One of the crucial elements in the soil for plant survival is soil water content (SWC). Radar system has advantages that can be implemented for measuring SWC in plantation areas. A radar system operates by utilizing electromagnetic waves to obtain the dielectric characteristics of the soil. However, the presence of tea plants has become an obstacle to the radar wave propagation toward the soil layer. Reflected signal, which is influenced by the presence of vegetation, makes the estimation of SWC inaccurate. Consequently, the estimation of SWC needs to consider the vegetation's effect. This study uses an FMCW radar system, which operates at a frequency of 24 GHz. A layer medium propagation model is proposed in this study to prove the relationship between the reflected signal and the SWC. The reflection coefficient extracted from the radar signal is used to estimate the SWC. The vegetation propagation constant was obtained from the average field measurement results. The gravimetric method is used to validate the SWC estimation in vegetation's presence using the radar system. The results of the field experiments showed that the proposed method succeeded in estimating the SWC by considering the presence of vegetation with an average error of 3.57%. The proposed method has the potential to be applied to plantation areas.

This paper presents the total gain and directivity control with port excitation in a 4×4 hexagonal split-ring resonator (H-SRR) MIMO antenna for dual-band operation in 2.4/5.2 GHz bands. The MIMO antenna is shown more than 15 dB isolation between antenna elements placed orthogonally, and a spacing was introduced between them to achieve higher isolation in the first proposed design, then, a Z-shaped structure of specific dimensions was inserted to further improve the isolation between antenna elements. The simulated and measured return losses and transmission coefficients confirmed the improved performances for impedance bandwidth and isolation. The gain, axial ratio, and radiation pattern performances of the 4×4 H-SRR MIMO antenna are studied by exciting different port combinations of the four ports of the proposed antenna. A wide range of gain and axial ratio variations are observed on exciting single, dual, triple, and quad-ports of the proposed MIMO antenna and discussed using the radiation patterns. Also, various MIMO parameters, ECC < 0.04, TARC < -10 dB, MEG < -6 dB, DG < 10 dB, and CCL < 0.4 bits per second per Hz, are found in the 2.4/5.2 GHz bands, which confirms the applicability of proposed H-SRR MIMO antenna with polarization diversity.

Nonlinear photonic sources including semiconductor lasers have been recently utilized as ideal computation elements for information processing. They supply energy-efficient way and rich dynamics for classification and recognition tasks. In this work, we propose and numerically study the dynamics of complex photonic systems including high-β laser element with delayed feedback and functional current modulation, and employ nonlinear laser dynamics of near-threshold region for the application in reservoir computing. The results indicate a perfect (100%) recognition accuracy for the pattern recognition task and an accuracy about 98% for the Mackey-Glass chaotic sequences prediction. Therefore, the system shows an improvement of performance with low-power consumption. In particular, the error rate is an order of magnitude smaller than previous works. Furthermore, by changing the DC pump, we are able to modify the number of spontaneous emission photons of the system, which then allows us to explore how the laser noise impacts the performance of the reservoir computing system. Through manipulating these variables, we show a deeper understanding on the proposed system, which is helpful for the practical applications of reservoir computing.

The article presents a multiband symmetrically placed two elements, inverted-F multiple inputs multiple outputs (MIMO) antenna for wireless LAN (WLAN), Industrial, Society and Medical (ISM) band, S-/C-band applications. Decoupling (S₁₂ < -15 dB) between the two antenna elements of MIMO antenna is improved by introducing metallic vias at the top ends of the patch. The MIMO antenna has been fabricated and measured on a piece of low-cost, low-profile, FR-4 substrate. A combination of parasitic loading of 4-units (quadruplet) of square-split ring resonators (SRRs) and complementary split ring resonator (CSRR) cells have been used to achieve quad-bands for lower than -10 dB total active reflection coefficients and additionally to improve isolation between antenna elements. The paper also presents the tabularized and graphical investigations of the analyzed and measured resultant MIMO parameters like; envelope correlation coefficient (ECC), diversity gain (DG), total active reflection coefficients (TARC), MIMO-VSWR (voltage standing wave ratio), channel capacity loss (CCL), etc. and are found approximately close to each other with small acceptable errors. The other important parameters (reflection coefficients, radiation pattern, E-plane and H-plane polar plots, electric field vector (E) distribution, and current density vector (J) distribution) of the proposed antenna were also demonstrated and measured using a vector network analyzer (Agilent N5247A VNA) and 18 GHz Anechoic chamber in the microwave research laboratory. The MIMO (1×2) antenna is best suitable for Bluetooth/WLAN/Wi-Fi (2.45-2.57 GHz) and ISM band, FIXED, MOBILE, RADIO Location, Amateur & Amateur-satellite service (2.45 GHz) within impedance bandwidth (S₁₁ < -10 dB) from 2.45-2.57 GHz lower band, and n46 (5.40-5.49 GHz) upper band.

In this paper, a compact antenna with wideband and wide beam is proposed. It is composed of a rectangular patch etched on a substrate, a feeding probe, two metal columns, and a ground plane. By inserting air gap between the substrate and the ground, as well as using the coupled feeding, wide impedance bandwidth is obtained. By inserting two metal columns on the two sides of the patch for inducing longitudinal current, the HPBW of the antenna in the operation bandwidth can be widened. Design evolutions are provided for the proposed antenna, and main parameters are investigated for obtaining the adjusting rules. For validation, a prototype operating at 5.8 GHz is fabricated, where the dimension is only 0.31λ₀ × 0.11λ₀ × 0.11λ₀. Measurement results show that a fractional bandwidth of 24% is achieved for |S₁₁| < -10 dB. In this bandwidth, the measured gain is larger than 2.5 dBi with a maximum gain of 3.5 dBi. At E-plane, the measured HPBWs are in the range of 130°~190°, and the values are around 120° at H-plane.

This article presents a simple method to introduce multiple Transmission Zeros in the stopbands of a triple passband Chebyshev filter and also suppress the spurious bands below a satisfactory level, so that it can be treated as a Quasi-Elliptic filter. A pair of Stub Loaded Step Impedance Resonators (SLSIRs) is used to produce the Chebyshev filter with central passbands at 2.5, 5.5, and 9 GHz. An asymmetric Non-Resonating T (NRT) structure is implemented on each of the SLSIR to achieve the improved skirt selectivity. Each non-resonating structure produces three Transmission Zeros (in total six). In addition to the satisfactory stopband performances, the Quasi-Elliptic triple band filter produces insertion losses of |0.4|, |0.6|, and |0.7| dB at three centre frequencies respectively. Simulation of the proposed filter is done using HFSS13 software, and to validate the simulation, a prototype is fabricated on an Arlon AD250 (Dielectric Constant 2.5, height 0.76 mm) substrate.

Optically transparent antennas have attracted increasing interest in recent years. However, the inherent ohmic loss of transparent conductor used in antennas will always introduce degradation of radiation efficiency. It is of most importance to find the optimization between the material loss and radiation efficiency. In this paper, we design and experimentally demonstrate a high-performance optically transparent dual-polarized cross dipole antenna over 3.4-3.8 GHz for 5G wireless communication based on the characteristic analysis of surface current distribution. By making current distribution uniform on the radiators and reducing the current on the ground, the mutual coupling between the elements is alleviated, and the radiation efficiency can be optimized. The proposed antenna is fabricated with 0.118-Ohm/sq meshed metal, and the optical transparency of antenna is 81%. The proposed antenna achieves a voltage standing wave ratio (VSWR) of less than 1.3, radiation efficiency of 72% (84% of pure copper) and a peak gain of 4.5 dBi (5.1 dBi of pure copper). Compared to current state-of-arts, the proposed antenna exhibits better performance of the figure of merit (FOM) in terms of the bandwidth, optical transparency and radiation efficiency. Our work paves the way to diverse application of beyond-5G wireless communication.