A deep learning linear sampling method (DLSM), composed of linear sampling method (LSM) and a convolutional neural network (CNN) of U-Net, is proposed to restore shape of multilayered scatterers with cylindrical or rectangular cross section. Simulations over random samples with different geometrical parameters are used to verify the efficacy of the proposed method.
To improve the performance (low torque ripple, high average torque and high efficiency) of the external rotor switched reluctance motor (ERSRM), a preference multi-objective optimization framework for design and control of an ERSRM based on CD-NSGA-II (Chi-square distance fast non-dominated sorting genetic algorithm) with gradient targets is investigated. Firstly, the structure of the ERSRM is introduced, and the comprehensive sensitive analysis that evaluates the influence of each design variable on optimization objectives is presented. Secondly, the initialization of population, cross-mutation method and sorting method of conventional NSGA-II are improved. Then, the practicability of this method was proved by standard test functions. Finally, the NSGA-II and CD-NSGA2-II are combined with the visual basic script (VBS) script to optimize the ERSRM, respectively. Finite-element analysis results confirmed the validity and superiority of the optimized design.
Broadband differences interferometeric analysis of a three-layer planar polymer optical waveguide is proposed and optimized to detect the concentration of hemoglobin in blood. The dispersion characteristic and cutoff film thickness of proposed waveguide are obtained by matching the field at various boundaries. The obtained cutoff film thickness for TE0 and TM0 modes is 0.09 µm, 0.1 µm at operating wavelength 400 nm, and 0.19 µm and 0.23 µm at operating wavelength 800 nm, respectively. The effective refractive indices of TE0 and TM0 modes are obtained at two considered wavelength i.e. 400 nm and 800 nm, and hence the difference of their propagation constant is calculated. It is observed that the propagation constant of these modes decreases with the increase of wavelength. Also, the difference of propagation constant attains its maximum value at certain wavelength and decreases either side of this wavelength. The interference maxima signals at output are considered as sensing signal. The maxima of interference signals, close to the maximum value of propagation constant, are shifted sufficiently with the change in cover refractive index. The maximum sensitivity 3.8 nm/RIU is obtained in the proposed broadband differences interferometeric analysis of waveguide at film thickness 300 nm. Hence, at this film thickness the sensing signal changes by 0.68 nm/g/L of hemoglobin concentration in blood.
This article presents a circularly polarized (CP) dual lens (DL) antenna with high gain and wide axial ratio (AR) bandwidth for automotive radar applications. Proposed antenna system provides low AR and scan loss over a wide angular range. It consists of a linearly polarized (LP), wide band, aperture coupled planar feed antenna, an extended hemispherical lens and a planoconvex lens with thin parallel plates and air slabs. In-lens polarizer mounted to the flat surface of the planoconvex lens converts LP wave to CP state. Fundamental design rules to obtain CP is defined. A CP DL design in low dielectric permittivity material (εr=3) is introduced. It achieves simulated efficiency that varies between 75 and 82% within the 77-81 GHz automotive radar band. AR is below 2.2 dB for all scan angles up to 25˚. Realized gain at boresight radiation is 25.6 dBic at the center frequency. 0.85 dB scan loss is observed at ±30˚ scan angle. A frequency-scaled prototype has been fabricated by additive manufacturing process with fused deposition modeling, and the concept is proved by the experimental results in 22-28 GHz band.
A novel metamaterial-based circular patch multi-input multi-output (MIMO) antenna is designed with a `C'-shaped defected ground structure for high isolation. A 4 × 4 mm2 unit cell for a ring resonator has been designed and exhibited double negative material (DNG) properties from 1.0 to 2.92 GHz and 13.68 to 17.67 GHz and Mu negative material (MNG) from 4.70 to 13.67 GHz. The proposed antenna structure is designed by embedding the ring resonator-based meta-structure to a circular patch antenna and fabricated with dimensions 0.245λ0×0.409λ0 (15×25 mm2). The proposed antenna operating at 8.50 to 14.23 GHz for X and lower Ku bands is used in the Unmanned Arial Vehicle (UAV's) applications. The spacing between elements is 0.088λ0 (5.4 mm) on an FR4 epoxy substrate, and the `C'-shaped structure on the back of the antenna improves the isolation of more than 24 dB in the operating band. Distance between the antenna elements plays a crucial role, and parameters affected by this are optimized by introducing machine learning. For future predictions, a linear regression model was created to optimize the parameters' linear dependencies like isolation and return loss on the distance between the antenna elements. The radiation efficiency and gain of the antenna are enhanced by 92% and 6.02 dB at 13.22 GHz, respectively. The MIMO antenna's simulated results of diversity and other parameters are in the acceptable range with the measured results used for X-band radar applications. The proposed decoupling technique is simple to understand and implement.
In this paper, minimum variance distortionless response (MVDR) algorithm for adaptive Beamforming is applied to a linear array under known mutual coupling among half wavelength dipole (HWD) antennas. This algorithm will minimize the signals from all interference directions while keeping the desired signal undistorted. The problem of calculating mutual coupling coefficient of the array HWD antennas formed into a matrix has been considered. The obtained results show the effectiveness of the proposed method, in which the optimum weighting of adaptive antenna arrays is accomplished by computing the weight vector that achieves maximum towards the desired signal and nulls towards interferers. Also, performance evaluation of this algorithm in terms of complexity, convergence speed, and amplitude response will be present. It is shown from the simulation results that the performance of the beamforming algorithm considering the mutual coupling effect can be improved by the proposed compensation method. We also simulate the signal-to-interference-plus-noise ratio (SINR) with different input signal-to-interference ratio (SIR). The different results obtained are in good agreement with those of the literature.
A compact size UWB circularly polarized (CP) dual-port MIMO antenna is designed for Ku/K band applications. The proposed antenna contains a revised circle-shaped slot from the radiation patch on the front-side and a stepped-feed line on the back-side of the substrate. The orthogonal position of the antenna ports allows us to produce isolation of more than 30dB and has a (-10 dB) impedance bandwidth of 68% (14.3-29.3 GHz) at two resonant frequencies 15.6 GHz and 24.7 GHz respectively. 3 dB ARBW in the operating bands is 14.6% and 6.7%, respectively. The total size of the MIMO antenna is is 0.1λ × 0.05λ × 0.003λ mm3 at a lower frequency. Diversity characteristics like ECC, DG, TARC & CCL are determined to confirm the MIMO antenna's work qualities. Ringing resonating frequencies are observed at lower operating bands and are responsible for gain degradation. The proposed antenna has excellent characteristics for satellite and NASA's Tracking Data Relay Satellite application.
The present work demonstrates the design of a wideband 2×1 reconfigurable beam steering array for wireless communication systems. The designed antenna is powered by a microstrip line, and consisting of a two rectangular-shaped radiating elements and a rectangular planar ground. Its dimensions are the following: 0.67λ0 x 0.53λ0 x 0.03λ0. It executes three reconfigurable operating states by turning on and off two PIN diodes to change the direction of the main beam, as well as a beam tilt ranging from (±30°) to (±38°). A progressive analysis in order to enhance the the antenna characteristic performances is furnished. The proposed reconfigurable antenna bandwidth is 18.18% (simulated), 18.84% (theoretical) and 19.42% (measured). The presented antenna has a maximum gain of 8.62 dB (simulated) and 8.45 dB (measured), and a higher efficiency ratio of 80% to 86% over the operating band (5 GHz-6 GHz). The designed antenna is fabricated using a low loss Rogers RT5880 substrate of 2.2 relative permittivity. The simulated, theoretical and measured results are presented and exhibit good accord, including the S11 parameter and radiation patterns. In addition to the pattern reconfiguration, the obtained results are useful in order to improve the overall gain, antenna bandwidth and efficiency.
Through-Wall-Imaging (TWI) radar offers considerable advantages for applications that require safety and security, such as disaster survivor rescue and tracking terrorist activities. In such situations, the use of an impulse UWB radar system is constantly increasing due to its ability to provide precise images of hidden targets in a short period of time. This paper presents a new radar system for through-wall imaging using an impulse-radio ultra-wideband (IR-UWB) signal. The radar system is built using a field-programmable gate array (FPGA) board, an oscilloscope, and Vivaldi antennas. The radar system transmits impulse signals, which have a monocycle shape with a 400-picosecond duration and a 4.6 GHz bandwidth. The FPGA board is used to produce impulse signals that have a short time duration in the sub-nanosecond range in order to expand the bandwidth of the generated signal and make the developed radar capable of providing high-resolution images. The FPGA-based implementation of the IR-UWB generator offers the flexibility to modify the spectrum characteristics of the generated signal. The receiver side of the radar system collects the echoes using the principle of synthetic aperture radar (SAR), and then the time-domain back-projection algorithm is applied to the radar echo to form 2D images. An indoor imaging experiment was carried out with two human targets to investigate the imaging capability of the designed IR-UWB radar. The obtained experimental results demonstrate that this radar has the potential to deliver high-resolution images of multiple human targets and identify their locations.
This paper investigates the electromagnetic coupling from various aperture shapes in aperture coupled suspended rectangular microstrip antennas. The proposed study involves various shapes of coupling aperture such as ``rectangle'', ``H'', ``bowtie'', and ``hourglass'' with a single-layer aperture coupled suspended rectangular microstrip antenna. Among the various shapes, ``hourglass'' shaped aperture yields maximum coupling leading to maximum bandwidth. For the validation aperture coupled suspended rectangular microstrip antenna with ``hourglass-shaped'' aperture is fabricated, and measurements were carried out. The measured fractional impedance bandwidth (FBW) with ``hourglass'' aperture is more than 30% at 1.06 GHz. Measured peak gain and front-to-back (F/B) ratio of aperture coupled suspended microstrip antenna with ``hourglass'' at 1.06 GHz are 8.5 dBi and greater than 11.2 dB, respectively. The influence on the antenna's performance parameters such as realized gain, impedance bandwidth, and F/B ratio due to metallic mounting surface is also investigated. The simulated and measured performances of the antenna are in agreement. The proposed investigation is very useful for various applications, when broadband antenna is mounted on a metallic body.
Finite-aperture microwave vortex beams of various structures in the near-, middle-, and far-field propagation zones have been simulated. The decay of external sidelobes leading to the end of non-diffractive propagation within a fraction of the near-field zone is observed. A ring source of the vortex beams with phase-shift and frequency-sweep control of angular modes and polarization patterns through the use of patch antenna arrays of varying polarization is suggested. A new form of the beam wavefront variation with azimuthal undulation has been proposed that allows one to significantly diversify and dynamically control the beam structure. The consequences of a limited number of antenna patches in a circular array have been considered. The effects of a gradual drop of radiation power along the array and the use of multiple feed points for improving the beams have been simulated.
This letter, an ultra-wideband compact printed log periodic dipole (LPD) array antenna is designed to operate between 500 MHz and 6 GHz frequencies. The proposed LPD antenna structure consists of one bow-tie dipole and 15 regular dipole elements. The bow-tie element is introduced to improve the antenna's performance at the lowest frequencies below 1 GHz and at the same time to reduce the antenna size maintaining a good performance. An experimental antenna prototype has been designed, optimized, fabricated, numerically and experimentally assessed. The obtained results are very promising, and they demonstrated that the presented antenna prototype is able to operate in the range between 500 MHz and 6 GHz with an average gain of 6 dBi and a very compact size.
While analyzing wideband electromagnetic scattering problems using ultra-wideband characteristic basis function method (UCBFM), the reconstruction of a reduced matrix and the recalculation of an impedance matrix at each frequency point cost a large amount of time. To overcome this issue, a novel method that combines UCBFM with compressive sensing (CS) is proposed in this paper to rapidly analyse the wideband RCS. The proposed method makes the ultra-wide band characteristic basis functions (UCBFs) generated at the highest frequency as the sparse basis, introduces the CS theory, randomly extracts several rows from the original matrix as the measurement matrix, utilizes the corresponding excitation vector as the measurement value, and then employs the recovery algorithm, through which the solution of target induced current can be obtained. Due to partial filling of impedance matrix and efficient recovery algorithm, the wideband RCS computation time of the object is significantly reduced using the proposed method. Furthermore, the numerical simulation results show that the computation efficiency for the target wideband RCS can be further enhanced compared with that of the stand-alone UCBFM.
In this article, a miniaturized pentagonal slot antenna (PSA) with a Meander Koch Defected Ground Structures (MK-DGS) and metamaterials (MTM) is proposed for 5 GHz WLAN application. Initially, a Meander Koch DGS was used to lower the resonant frequency of the basic PSA, from 13.1 GHz to 5 GHz. The proposed antenna has been 61.83% miniaturized, close to an electrically small antenna. The performance characteristics of a basic PSA using MK-DGS and MTM superstrate, which improves efficiency, directivity, and peak gain, are also discussed. An antenna with dimensions of 15 × 15 mm2 (or) 0.25λ0 × 0.25λ0 mm2 at a thickness of h1 = 1.6 mm is designed, fabricated, and tested on an FR4 epoxy substrate, and its impact on size reduction performance is evaluated. The gain at 5 GHz is increased from 3.15 to 7.84 dBi by introducing an MTM superstrate made of RT Duriod at a thickness of 1.575 mm above the miniaturized PSA at 17 mm. Test results of the prototype model are corroborated by the simulated results of the proposed model.
In this paper, a quad-band notch characteristics ultra-wideband (UWB) antenna for Wi-MAX, L-WLAN, U-WLAN, and C-band applications is presented. The initial UWB antenna bandwidth is achieved in the 2 to 12.5 GHz frequency band by using the partial ground method. Spiral lossy resonator (SLR) slots are loaded into the UWB ground structure to achieve quad-band notch characteristics. Each SLRS circuit is accountable for a single notch characteristic by losing EM power at the notch frequency. A quad-band notch is accomplished in this antenna for WiMAX (3.24 to 3.56 GHz), L-WLAN (4.76 to 5.34 GHz), U-WLAN (5.58 to 5.91 GHz), and C-band (7.37 to 7.71 GHz) by loading four SLR slots circuits into the UWB antenna. The proposed antenna is engraved on a Rogers RO4003C (3.55) substrate having an overall volume of 50*40*1.524 mm3. The proposed antenna's performance has been verified through simulation and experiments.
The limited space of the substation contains a lot of electrical equipment and voltages ranging from hundreds to several thousand volts, resulting in a complex electromagnetic environment in the substation. As the deployment of 5G base stations increases in substations in China, the power-frequency magnetic field in substations will cause problems, resulting in a location problem. This paper develops a circuit model for converter stations, and presents a calculation method that considers the geomagnetic permeability, 3-phase transmission mode, and erection direction influences. The correctness of the calculation method in this paper is verified by comparing the simulation results and calculation results of the substation model. The deployment conditions of 5G base stations in the substation are analyzed according to the national standard of the requirement and measurement methods of electromagnetic compatibility for mobile telecommunications equipment Part 17: 5G base station and ancillary equipment.