Within the framework of the first-order small perturbation method, we derive the statistics of the layered rough surface index and the normalized difference polarization index for three-dimensional layered structure with slightly rough interfaces illuminated by a monochromatic plane wave and for multilook returns. We establish closed-form expressions for the probability density function and the cumulative distribution function. The first- and second-order moments are given by relation recurrences. We validate from Monte Carlo simulations the obtained theoretical formulas.

This work aims for nonionizing radiation assessment to reduce Specific Absorption Rate (SAR) in the IEEE SAM phantom using MIMO antenna. The traditional copper material MIMO is designed with mode characteristics and validated for 2.4 GHz in this experiment. The MIMO antenna, when placed near SAM phantom and SAR, is estimated. Copper-based antennas are replaced by nanomaterial-based antennas, such as graphene, multi-walled carbon nanotube (MWCNT), and single walled carbon nanotube (SWCNT), to study SAR behavior. SAR is reduced using Nanomaterial based antenna in which SWCNT significantly reduces SAR up to 66 percent using Altair's Feldberechnung für Körper mit beliebiger Oberfläche (FEKO).

In this paper, we devise a phased array antenna with liquid crystal material, employing a 10×10 uniform rectangular array. The phase of the phased array antenna is controlled by loading bias voltage on the liquid crystal layer, and the FoM (figure-of-merit) of the phase shifter can attain 70.6°/dB. The phased array antenna works at 16 GHz and employs a microstrip circular patch as the radiation unit. The proposed phased array can achieve a gain of 23.1 dBi, and its beam scanning range reaches ±45° in simulation experiment. The preliminary measurement results demonstrate that the performance of the proposed antenna is basically consistent with simulation results.

Aperture efficiency determines the percentage of radiation power incident upon the antenna available at the feed-point. Because the geometry of reflector is fixed, the behavior is primarily a function of the feed. The feed line that connects (transmit/receive) RF to the feed becomes an integral part of the system, so achieving maximum aperture efficiency depends on the capacity of feed line. This paper proposes a microstrip feed line behavioral model for parabolic reflector antenna systems, using an open loop characterization approach. Dielectric material loss intensity varies from material to material. This is consequently used for the effective design of feed line, because characteristic impedance of transmission line varies with material type and the material properties. This causes the reflection loss due to mismatched impedance at the source and load. Loss tangential factor of each material has significant effect on the loss profile. The developed model is analyzed with losses of the feed pattern, and the distance between the edge and the vertex. The proposed attenuation factor can be used to predict loss intensity per feed line length, at different terrestrial and satellite communications frequency bands.

Coupling coefficient is a key parameter for the coil design of wireless power transfer (WPT) systems. The accurate calculation of coupling coefficient is an important theoretical basis for optimizing the coil structure and improving the transmission efficiency in WPT systems. In this paper, the magnetic flux density distribution of rectangular spiral coils with double magnetic shielding is studied, and an analytical model of coupling coefficient between arbitrarily positioned rectangular spiral coils is established. First, the incident magnetic flux density is obtained based on the dual Fourier transformation and the relationship between the magnetic flux density and magnetic vector potential. Second, the reflected magnetic flux density in the region of the receiving coil is solved by using Poisson's equation, Laplace's equation and boundary conditions. Finally, the formula for the coupling coefficient between rectangular spiral coils is derived by the spatial frame transformation method and the integral method. The calculation results agree well with the finite element simulation value and experimental measurements, which verifies the correctness of the calculation formula of the coupling coefficient.

In the next few years, the use of drones for civilian applications is expected to skyrocket, leading to a multitude of new use cases. However, the possible improper use of drones generates doubts in the population due to the risks it poses to the safety and security of airspace operations. Having absolute surveillance of unmanned aircraft is quite difficult for several reasons, e.g., problems arise when monitoring small drones due to their reduced radar signature, around -10 dBm², which makes them practically imperceptible to Air Traffic Control (ATC) radars, which can rarely detect targets with radar cross-sections (RCSs) below 0 dBm². For instance, a possible solution to mitigate the lack of identification and thus avoid problems specially in Control Traffic Region (CTR) zones is to increase the RCSs of the drones by incorporating a reflector element that could produce much more intense radar echoes than the drone itself. The aim of this paper is to design and evaluate a Luneburg lens through electromagnetic (EM) simulation and validate its performance experimentally by conducting flight tests in open space with a commercial drone carrying the manufactured reflector making use of a 24 GHz radar.

A wideband, compact and flexible conformal circularly polarized antenna (CCPA) with ground plane is proposed in this letter. It consists of a polygonal patch, two V-shaped coupling feed lines, a phase-shift transmission line and two layers of metallic ground planes. Two resonant modes are generated by cutting one vertex of the octagonal patch to broaden the operational bandwidth. An L-shaped ground plane is designed on the back of the top substrate. This configuration can obtain a relatively compact phase shifter on the one hand and make the coupling branches and octagonal patch share one ground plane on the bottom, improving the thickness of the antenna which yields wide bandwidth on the other hand. The CCPA can own good performances both in the planar and cylindrical carriers. Under the cylindrical conformal circumstance, the measured |S₁₁| and axial ratio (AR) bandwidth reach 12.05% (5.5 GHz-6.205 GHz) and 8.93% (5.67 GHz-6.2 GHz), respectively. The measured gain is 8.5 dBic with 3 dB gain bandwidth covering the whole operational band.

In this work, we analytically enhanced the channel capacity and bandwidth of an MI waveguide system by using multi-layer coils (MLCs) and spread resonance strategy. In this analysis, we considered the practical constraints like parasitic capacitance, ac resistance, skin and proximity effects and inductance of multi-layer coil. The bandwidth is significantly enhanced up to 6 KHz, and a trade-off is observed between the bandwidth and achievable transmission range. Besides, the influence of coil turns, layers and the impact of spread intensity are analyzed. Furthermore, we introduced a new MLC structure with thin-rectangular cross section which has promising characteristics like higher magnetic flux, low ac resistance, and high inductance. The performance of this coil is compared with that of existing round circular and tubular multi-layer coils. These characteristics are comparatively studied through simulations performed in ANSYS Maxwell R21. Based on the results we infer that the proposed coil is more advantageous than the existing standard MLC for MI communication in terms of cost and system performance.

In order to improve the electromagnetic performance of permanent magnet vernier machines (PMVMs) at a high pole ratio, a novel U-type permanent magnet (U-PM) vernier machine with high-temperature superconductor (HTS) bulks is proposed. HTS bulks are introduced between the stator modulating teeth, and alternating flux bridges and U-PMs are added in the rotor yoke. The structure can reduce the magnetic flux leakage, provide a magnetic circuit for the low pole pair working magnetic field, weaken the magnetic barrier effect, and improve the torque density of the machine. The parameterized model of the proposed machine with 23 pole pairs of the rotor and 4 pole pairs of the stator is established by the finite element software. In addition, some key parameters of the proposed machine are layered by parameter sensitivity analysis, and then the machine is optimized by genetic algorithm. Compared with the conventional machine, the proposed machine increases the average electromagnetic torque by 69%, reduces the torque ripple to 1.7%, increases the power factor to 0.73, and increases the efficiency to 85.3%.

This paper thoroughly studies the realization of the reconfigurable function of RLSA antennas in terms of beamsteering at the frequency of 5.8 GHz. In the first step, the study on the characteristic of small RLSA antennas concludes that maximum beamsquint that can be achieved is around 70˚. In the second step, in order to minimize the size of reconfigurable RLSA antennas, a new technique of cutting a small RLSA into sectors is introduced. The analysis on the quarter cut RLSA and the semi cut RLSA shows that their performances do not deviate too much from the full circle RLSA performance. In the third step, study on the most suitable method of realizing the reconfigurable function of RLSA antennas chooses the method of implementing antenna array as the most suitable method. Based on this method, a structure of reconfigurable RLSA antennas is proposed. In the last step, utilizing the proposed structure and four quarter cut RLSA elements, a novel reconfigurable RLSA antenna in terms of beamsteering is simulated and fabricated. To avoid significant coupling effect between the antenna elements, all elements are separated by 20 mm. The antenna has a directivity of 9.2 dB, an efficiency of 97.95%, a bandwidth about 1.5 GHz, the mainlobe direction (in elevation direction) of 45˚, the beamwidth of 32.5˚, and the sidelobe level -6.3 dB. The beam of the reconfigurable antenna can be steered into four different azimuth directions, which are 0˚, 90˚, 180˚, and 270˚. Furthermore, a similar radiation pattern and reflection coefficient between the measurement and simulation verifies the validity of the study.

We extended the previous 2D method of BBGF-MST (Broadband Green's function-Multiple Scattering Theory) approach to 3D problems in periodic structures. Band Structures and Band Field Solutions are calculated. A feature of BBGF is that the lattice Green's functions are broadband so that the coefficients of the spherical wave expansions are calculated rapidly for many frequencies. These are then used for speedy calculations of the matrix elements of the KKR (Korringa-Kohn-Rostoker) eigenvalue equation. Using BBGF-MST, a low order matrix eigenvalue equation for the bands is derived. For the first two bands, the dimension of the KKR matrix equation is only 4 by 4. With the use of BBGF, the CPU requirement for the BBGF-MST technique is 0.27 secondson a standard laptop for solving the KKR eigenvalue equation. Numerical results of the band diagrams are illustrated. Higher order spherical waves are next used to calculate the normalized band field solutions for the entire cell.

This paper proposes an underdetermined direction of arrival (DOA) estimation for multiple input and multiple output (MIMO) sparse additive white Gaussian noise (AWGN) channels. Accurate DOA estimation helps in better signal analysis and noise cancellation in the channel. A novel multiplicative multi-kernel basis vector-based non-negative sparse Bayesian learning (NNSBL) algorithm is implemented over a predefined grid. Simultaneously stochastic cuckoo search algorithm (CSA) is exploited virtually to improve the DOA approximation for a non-uniform linear array (NULA) geometry by an optimized antenna reconfiguration model. The simulated and experimental results show that the proposed algorithm yields an optimized root mean square error (RMSE) for different optimized wavelengths of the randomly generated signals. The RMSE convergence graphs demonstrate the effectiveness of the new method for different signal-to-noise (SNR) values.

This study investigates several substantial questions arising in the diffraction by circular surfaces with the fractional boundary condition, which is the generalization of Dirichlet and Neumann boundary conditions. The study analyses the electromagnetic E-polarized plane wave diffraction by a slotted circular cylinder with the fractional boundary condition. For the first time, the fractional boundary condition regarding circular geometries is employed in the literature. The resonance characteristics for different boundary conditions, angle of incidence, and aperture sizes are analyzed. The new resonances are observed when the surface is different from the perfect electric or magnetic conducting surface.

This paper presents a novel localization method in multiple-input multiple-output (MIMO) systems based on the implementation of passive repeaters. In addition to their ability to enhance performance in MIMO systems by enriching scattering in line-of-sight MIMO environments, and extending coverage area and accessing blind spots in none line-of-sight MIMO environments, passive repeaters can help in localizing users by taking advantage of their spreading in the communication environments. In the proposed method, the target area is divided into a grid. Each location in this grid has a unique field interference created by repeaters. Because of the unique field interference, each location causes a unique field signature at the base station when a user in that location transmits signals. The field signature corresponding to the center of each grid cell is used as a fingerprint for localizing users in that cell, and for all cells, a bank of matched filters corresponding to all stored fingerprints is constructed. Using only the spatial coherence of the measured fields, there is no need for synchronization between users and the base station. When a signal arrives at the base station, the generated field signature is correlated with the bank of matched filters, and the location is determined based on the maximum correlation value. The numerical analysis is performed to verify the validity of the proposed method, and it is found that by means of passive repeaters, the user location can be determined with no need of calculating additional parameters.

This paper introduces and validates a compact two-dimensional Electromagnetic Bandgap (EBG) structure for the improvement of signal integrity (SI) and power integrity(PI) by suppressing Simultaneous Switching Noise (SSN). SSN bandwidth can be increased by using the proposed T bridge compact planar structure. The proposed structure is simulated using Ansys HFSS Software. Simulated and measured results by Vector Network Analyzer provide 3.13 GHz to 11.40 GHz frequency bandgap with good mitigation of SSN at -30 dB noise suppression reference. It will almost cover S, C, and X bands from electromagnetic frequency spectrum. This will be useful for satellite and terrestrial communication and radar communication applications. The proposed structure analyzes signal integrity issues using eye diagram in MATLAB and power integrity in HFSS with input impedance respectively. The main purpose of this work is to provide a compact structure to improve signal and power integrity by the suppression of power/ground noise. Comparative study is also performed with the proposed structure and reference board with similar dimensions.

This paper presents a proposal for a high birefringμeμnce photonic crystal fiber (C-PCF) with a doped liquid into two first ring holes, which is analyzed by the finite element method. It is demonstrated that the proposed fiber has a birefringence value of about 2.643 × 10^-2 at wavelength λ = 1.55 µm and temperature T = 25˚C. Also, a high chromatic dispersion of -272 ps/nm/km, an effective area of 1.693 µm², and a confinement loss of 0.058 dB/m for the x-polarization method were obtained at the same wavelength and temperature. The temperature influence on the modal properties has also been studied. We will demonstrate through the result that the fiber we propose can be used in both sensing and chromatic dispersion applications such as flattened dispersion fibers.

Breast cancer is, by far, the most diagnosed disease for the death of women worldwide. Researchers are working with an alternative technology to detect the tumours before it reaches the terrible stage because of the numerous limitations in the current imaging approach. This article suggests a promising technique by utilising non-ionizing microwave signal and artificial intelligence especially deep learning algorithms for early detection of breast cancer. This contribution will present a method to detect and classify the tumour category using backscatter signals obtained from antenna simulation in CST microwave studio software. The post-processed scattering parameters are utilized to create image through MATLAB programming environment. The high intensity in the image represents the precise position of tumour. The automatic classification of tumour is achieved by YOLOv5 deep learning model from the created microwave images. A training dataset with fifty image samples are formed by preprocessing and then augmentation is applied to create final dataset with 1000 samples. This approach can identify the location and type of early-stage tumour with size of 5 mm.

This letter presents a wideband polarization reconfigurable antenna based on liquid metal (LM) switches. It consists of single-fed crossed bowtie dipoles, a parasitic element grounded via a metallic post, a dual-cavity-backed reflector and liquid metal switches. The two arms of one dipole are loaded with two symmetrical identical slots, and on top of the slots, two sets of fixed-length movable liquid metal columns filled in polytetrafluoroethylene (PTFE) tubes are attached as switches. The altering between linear polarization (LP) and circular polarization (CP) can be achieved by changing the positions of the liquid metal switches. The dual-cavity structure is applied to obtain unidirectional radiation and enhance the circularly polarized performance. A prototype with overall size of 127 × 127 × 57 mm³ is designed and fabricated. The measured results indicate that the impedance bandwidth (IBM) of the antenna is from 1.06 to 2.46 GHz (79.54%) and the axial ratio bandwidth (ARBW) is from 1.39 to 1.91 GHz (31.52%) for CP state. In addition, the IBW for LP state is from 1.06 to 2.30 GHz (73.81%). Moreover, the peak gains can reach 7.73 dBic in CP state and 9.21 dBi in LP state.

Electromagnetic scattering of a Gaussian beam wave from an array of parallel homogeneous anisotropic circular cylinders is presented. The transmitted fields in the anisotropic cylinders are expressed as an infinite summation of eigen-plane waves with different polar angles. The expression of the Gaussian beam is represented as a product of a well-known scattering of a plane wave and a weighting function. The incident field is expressed in local cylindrical coordinates and the scattered field is the summation of contribution of all cylinders. Using the addition theorem of Hankel function, the expression of the scattered field can be transformed from local coordinates to others. By enforcing the boundary conditions on the surface of each cylinder, an infinite set of equations is obtained which can be written in a matrix form. Scattering cross sections and near fields are analyzed and compared finally.

In this paper, a new space-time adaptive processing (STAP) method based on improved nested arrays and pulses configurations is proposed. Specifically, we first decompose the sensor array into two uniform linear arrays (ULAs) plus a separate sensor, similarly for pulse trains. Then, the original received signals from the physical array and pulse trains are introduced into the virtual domain, where the virtual clutter plus noise covariance matrix (CNCM) estimation is performed. Since the system has more virtual sensors and pulses from the perspective of virtual domain, the degrees of freedom (DOF) capability is effectively enhanced to improve the angle and Doppler resolution of radar. With the spatial-temporal smoothing technique, the STAP filter is designed by reconstructing the CNCM and virtual signal steering vector. Simulation results validate the effectiveness and superiority of the proposed algorithm.