A compact metamaterial-loaded wideband monopole antenna is reported in this paper for wireless applications. Initially, a monopole antenna with a single stub was designed to resonate at 4 GHz. Still, it suffers from low gain, so to enhance the antenna parameters, a metamaterial unit cell was considered along the feed line and ground plane. Double split ring resonator (DSRR) is a modified unit cell of a typical split ring resonator (SRR) designed to achieve a good coupling effect. The dimensions of the proposed DSRR unit cell are 0.17λ0 × 0.17λ0, where λ0 is the free space wavelength at 4 GHz. It achieved an impedance bandwidth (-10 dB) in the frequency range of 3.38 GHz to 4.08 GHz & 4.64 GHz to 5.2 GHz, having a 19.49% bandwidth in the 1st band and 11.7% bandwidth in the 2nd band. A wideband was achieved in the frequency range of 3.39 GHz to 5.13 GHz with 47.9% bandwidth when the number of stubs was increased to four. A maximum gain of 3.3 dBi was attained with bidirectional radiation in the E-plane, and it was omnidirectional in the H-plane. By increasing the number of stubs, two resonant modes were merged, making it wideband and suitable for WLAN applications like Wi-Fi & WiMAX & Satellite Communications.
In this manuscript, quad port highly isolated sextuple-band notched ultra-wideband (UWB) multiple input multiple output (MIMO) antenna is designed and experimentally investigated. The suggested design employs four antenna elements fabricated over a Rogers RT Duroid 5880 substrate and placed orthogonal to each other by deploying polarization diversity technique for good isolation. By combining polarization diversity technique with a fan shaped de-coupler isolation could be improved even more. Ameliorated frequency selectivity of notch bands can be accomplished by loading each antenna element with four U-shaped slots and C-shaped stubs adjacent to the feed line to exhibit band rejection of 3.18-3.51 GHz (9.86%), 3.71-3.99 GHz (7.27%), 4.59-4.76 GHz (3.63%), 5.18-5.34 GHz (3.04%), 7.47-7.74 GHz (3.55%), and 9.29-9.55 GHz (2.76%) to surmount the possible intrusion from WiMAX, C-band, INSAT, WLAN, X-band, and radio navigation (RN) band. Besides, an RLC equivalent circuit has been examined by correlating with the outcome of the reported notch band UWB-MIMO antenna that evinces highly selective notch bands. The suggested antenna works in the frequency range of 2.1-11.2 GHz which is suitable for UWB applications. Simulation and experimental validation is done to analyze the response of the suggested antenna with respect to notch frequencies, current distributions, peak gain, radiation patterns, envelope correlation coefficient, diversity gain, mean effective gain, total active reflection coefficient, channel capacity loss, and multiplexing efficiency.
In this article, two antennas having partial ground plane, slot loading with microstrip line feeding are proposed for wireless and biomedical applications. Antennas resonate at 2.4 GHz with two different bandwidths. The first antenna having 20% bandwidth, i.e., the Ultra Wide Band (UWB) of 2.10 GHz-2.61 GHz that can be utilized for wireless application and the Federal Communication Commission (FCC) allotted band of 2.36 to 2.39 GHz for medical applications falls in this range. The UWB antenna has undergone additional tuning to make it appropriate for biomedical application. Additionally a parametric analysis of antenna's slot length, width and dielectric constant is performed to optimize the performance characteristics. The antenna is fabricated and tested using Vector Network Analyzer. The acquired results from simulation and measurement are in close match.
This paper presents the general numerical dispersion relationship for the three-dimensional (3-D) Radial Point Interpolation (RPIM) method in lossy media. A similar analysis has also been carried out and compared with the traditional Finite-Difference Time-Domain (FDTD) method. Both methods investigate dispersion, numerical loss, and anisotropy versus electric conductivity. The RPIM reveals lower numerical loss errors (NLE) in a wide conductivity range at the considered frequency. Furthermore, the numerical experiments show that a slight increase in the conductivity, for the lossless case, has almost removed the numerical anisotropy dispersion, which improves the numerical resonance frequency precision. Therefore, this effect can be used as an anisotropy optimization technique for lossless media. Based on a close examination of the experimental results around the resonant frequency, the numerical error for the lossless case was divided by ten. As a result, the experimental and theoretical resonance frequencies are found to be in good agreement.
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.
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.
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.
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.
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.
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.
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.
An outer rotor coreless bearingless permanent magnet synchronous generator (ORC-BPMSG) is a multivariable, nonlinear, and strongly coupled system. In order to realize the precise control of the ORC-BPMSG, a decoupling control strategy based on online least squares support vector machine (OLS-SVM) inverse system and internal model controllers is proposed. Firstly, on the basis of introducing its operation principle, the mathematical model is established. Secondly, on the basis of analyzing its reversibility, a real-time inverse system of ORC-BPMSG is obtained by using OLS-SVM, and it is connected in series with the original system to form a pseudo-linear system, which realizes the linearization and decoupling of the ORC-BPMSG. Thirdly, the internal model controller is designed to perform closed-loop control of the pseudo-linear system. Finally, the simulated and experimental results show that the proposed control strategy has better stability and decoupling performance than the decoupling control strategy based on the LS-SVM inverse system and PID (Proportion Integral Derivative).