In this paper, a broadband circularly polarized (CP) microstrip antenna array for S-band is proposed. The antenna consists of a parallel rotating feed network, sixteen units with cut corners, adding rectangular perturbations, and the guided patches with 45˚ oblique rectangular slots. The guided patches increase the impedance bandwidth of the antenna, and the feed network with a 90˚ phase difference increases the axial ratio bandwidth. The simulation and measurement results show that the S₁₁ curve is 2.45~4.15 GHz; the impedance bandwidth is 51.5%; the frequency with the axial ratio less than 3 dB is 2.54~3.74 GHz; the working bandwidth is 1.2 GHz; the CP bandwidth is 38.2%; the gain is 18.72 dB at the S-band center frequency. The advantages of the designed antenna are high gain, wide bandwidth, and a good radiation pattern. It can be applied to early warning radar in S-band. It also completely covers China Mobile's 2.6 GHz spectrum and can be used as a base station antenna if taking no account of the polarization method. The antenna has a simple structure, which is suitable for applications.

This paper presents a low-profile, flexible and wearable slot antenna for on-body communication. The proposed antenna is designed on a thin polyamide substrate of 0.25 mm height, which is flexible, elastic, and robust in nature. A rectangular patch with different slots acts as the main radiator, and partial ground acts as the bottom conducting plane for the proposed antenna. The designed antenna was able to resonate in the desired frequency band with a good return loss (S₁₁) by modifying the size of the ground plane along its width and placing a small cut on the ground. The designed antenna achieved a good -10 dB impedance bandwidth of 710 MHz and a peak gain of 7.2 dBi at 5 GHz. The designed antenna was checked for detuning in a bending scenario. The specific absorption rate (SAR) was evaluated, and the values were found to be within standard limits. The designed antenna was fabricated and tested in this study. The results showed good agreement between the simulated and measured values of the antenna parameters. The small size, low weight, and flexibility of the proposed antenna make it a good candidate for wearable devices in the WLAN/WBAN environment.

A systematic study of a low SLL (sidelobe level) two-way pattern in shared aperture arrays is presented. Three or two-weight excitations are used for the elements of the transmit and receive arrays depending on the requirements. The receive array has a smaller number of elements by not receiving from some of the edge elements of the transmit array. The condition of appearance of certain minor lobes of the transmit array pattern at certain nulls of the receive one helps to find the ratio between the number of elements of the receive and transmit arrays. In the case of more than one possible ratio, the optimum ratio is the one that gives the lowest SLL. In the three-weight array the total number of the transmit elements is equal to the that of the two higher excitations plus the number of elements of the highest one. In the two-weight excitation the higher weight elements of the transmit array are chosen to be approximately one half of the total elements. The excitations of both arrays are found by equating the level of the higher two unequal sidelobes of the two-way array factor. The three-weight array design is presented for the first time while the two-weight case gives lower peak SLL than those of the literature. Our work contains the important steps of the design and the main aspects of the implementation. The resulting peak SLL of the two-way array pattern reaches up to less than -51.2 dB and less than -56.5 dB, for the two- and three-weight cases, correspondingly.

In this paper, a flexible 2-port MIMO antenna with dual band-notched properties is designed and built for wireless body area network applications. The antenna's performance in its flat and bent states is measured using liquid crystal polymer as a substrate. Two UWB slot antenna components are arranged parallelly with linked ground. Furthermore, to achieve high port isolation, a decoupling device in the form of a fence is positioned between two antenna units. The measured operating bandwidth can reach 3.0-15.7 GHz, with blocking bands of 5.0-6.5 and 7.0-7.9 GHz. Port isolation (S₂₁) is better than 20 dB. This antenna has fine radiation properties, high isolation, and flexibility, according to the bending and flat antenna tests. It has a promising future for wearable Internet of Things applications.

In order to reduce the multipath fading caused by the reflection of various obstacles in short-distance communication, this paper designs a quaternion MIMO millimeter wave antenna working at 28 GHz. The antenna design adopts an inverted trapezoidal radiation patch and a slotted trapezoidal ground plate structure, so that the S₁₁ of the antenna is lower than -10 dB in the frequency band of 24~32 GHz. By using a 1×2 array structure as the unit of MIMO antenna, the gain of the antenna at 28 GHz is 7.5 dBi. The isolation degree of each port is lower than -25 dB by orthogonal placement of each unit. The performance of the antenna is tested by the physical production test. The actual test results show that the operating bandwidth of the antenna is consistent with the simulation results. The gain at 28 GHz is slightly lower than the simulation results by 0.1 dBi, and the isolation of each port is lower than -18 dB, which is 7 dB away from the simulation results but still meets the requirement of -15 dB for MIMO communication. The measured results show that the antenna can be used in MIMO short-distance communication system.

As one of the most important technologies for the next generation very-large scale integrated circuit fabrication, extreme ultraviolet (EUV) lithography has attracted more and more attention in recent years. However, in EUV lithography, the optical distortion of the printed image on wafer always has negative impacts on the imaging performance. Thus, to enhance the imaging performance of EUV system, especially for small critical dimensions, in this work, a novel optical proximity correction (OPC) system based on the deep learning technique is proposed. It includes a forward module and an inverse module, where the forward module is employed to fast and accurately map the mask to the corresponding near field of the plane above the stack to help the construction of training dataset for the inverse module operation, and the inverse module is employed to fast and accurately map the target printed image to the corrected mask. Numerical examples demonstrate that compared with traditional full-wave simulation, the forward module can greatly improve the computational efficiency including the required running time and memory. Meanwhile, different from time consuming iterative OPC methods, the corrected mask can be immediately obtained as the target printed image is input using the trained inverse module.

On the basis of artificial magnetic conductors (AMCs), a dual-band MIMO antenna is suggested. For WBAN and WLAN applications, the frequency ranges supported by this antenna system are 2.36-2.51 GHz and 5.03-6.12 GHz. The proposed dual-band MIMO antenna is made up of two vertically positioned dipole antenna elements. A simple double circle-based AMC array is suggested to decrease radiation exposure to people while increasing forward gain. The antenna and the 3×3 AMC array are both printed on an FR4 substrate. The presented antenna with the AMC structure is manufactured and measured in order to confirm the simulated results in terms of S-parameters, radiation patterns, gain, and diversity parameters. According to the measurements, the suggested antenna exhibits peak gains of 3.34 dBi and 7.48 dBi at 2.45 GHz and 5.8 GHz, respectively. The SAR value of body tissue can be reduced by around 99% while the front-to-back ratio (FBR) is noticeably enhanced. The proposed AMC-supported MIMO antenna is applicable for WBAN and WLAN applications based on the above good performances.

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.