This study presents a novel design for a dual-band antenna that is compact, efficient, and suitable for both WLAN and WiMAX applications. The antenna features a circular patch with a Hilbert fractal structure and a coplanar waveguide feed line, resulting in a compact size of 24x34x1.6 mm3. By utilizing a Hilbert fractal slot and defected ground structure, the antenna can operate in two frequency bands, 2.39-2.47 GHz and 3-6.32 GHz, providing coverage for the desired WiMAX and WLAN bands. The experimental results demonstrate acceptable gains and high efficiency at the resonant frequencies, along with omnidirectional radiation patterns in the H-plane and bidirectional patterns in the E-plane. Notably, this design offers a nearly 50% reduction in size compared to comparable antennas and higher gain, representing a significant contribution to the field of dual-band antenna design.
Attenuation caused by various weather conditions and atmospheric turbulence significantly reduces the performance and reliability of free space optics (FSO) link. This paper employs simulations to analyze the signal quality of the proposed FSO link under various climate conditions. The performance analysis and parametric evaluation of the proposed 25 Gbps DP-QPSK based CO-OFDM FSO link with and without the spatial diversity technique is carried out. Also, we have compared the proposed FSO link with the 16-QAM-based OFDM FSO link for the vivid atmospheric conditions. The simulation results are analyzed in terms of key performance metrics such as bit error rate (BER), signal-to-noise ratio (SNR), link distance, received power and reliability. The results show that the FSO link with spatial diversity is more effective towards mitigating the adverse effects of atmospheric attenuation and turbulence in comparison with FSO link without diversity and 16-QAM OFDM-based FSO link. In total, this results in lower BER, higher SNR, improved received power and increased reliable distance for practical FSO communication system.
Microwave imaging radar systems are often required for the recognition of hidden objects at various job sites. Most existing imaging methods that these systems employ, such as beamforming, diffraction tomography, and compressed sensing, which operate on synthetic aperture radar, produce highly distorted radar images due to the limitation of the frequency range, size of the array, and attenuation during the propagation, and thereby become hard to interpret the description of the object. Several methods explored for the recognition of hidden objects are based on deep neural network models with millions of parameters and high computational costs that render them unusable in portable devices. Moreover, most methods have been evaluated on datasets of microwave radar images of hidden objects with the same relative permittivity, orientation, size, and position. In real-time scenarios, objects may not have similar relative permittivity, orientation, size, and position. Due to variation in the object's relative permittivity, orientation, size, and position, there will also be variation in the reflectivity. Consequently, it is hard to say if those algorithms will be robust in real-world conditions. This paper presents a novel shape-based approach for recognizing hidden objects which combines delay-and-sum beamforming with an artificial neural network. The merit of this proposed method is its ability to simultaneously recognize and reconstruct the object's actual shape from distorted microwave radar images irrespective of any variation in relative permittivity, orientation, size, and position of hidden object. The performance of the developed technique was tested on a dataset of microwave radar images of various hidden objects having different relative permittivities, sizes, orientations, and positions. The proposed method yielded an average reconstruction rate of 91.6%. The proposed method is appropriate for evaluating occluded objects such as utility infrastructure, assets, and weapons detection and interpretation, which have regular shapes and sizes of the cross-section at various construction, archaeological and forensic sites.
In the present era of wireless communication networks, the key area of concern is always the need for faster data rates to meet the growing requirements. The 5G standards have the fortitude to bring about rapid data transfer speeds, instantaneous connectivity, large data capacities, and minimal latency. In this paper, a novel octal patch integrated with a bow-tie parasitic antenna element with full ground plane that incorporates a microstrip dual band antenna was proposed for 5G n257/n261/n259 and n260 band applications. This bow-tie parasitic antenna element integrated octal patch single and MIMO antenna structure was mounted on an RT Duriod 5880 (εr = 2.2, loss tangent = 0.0009) with dimensions of 7.5 x 9.9 x 0.9 mm3 and 7.5 x 19.8 x 0.9 mm3 (0.67λ x 1.75λ x 0.07λ, where λ is considered at the lowest operating tuned frequency). A decoupling element was precisely placed in the core of a two-element MIMO antenna to reduce the mutual coupling. This embedded antenna radiating structure resonated in dual bands ranging 26.69-29.55 GHz and 38.24-42.53 GHz with a center frequency of 28 GHz and 40.2 GHz, respectively. This achieves a bandwidth of 2.85 GHz (10.3%) and 4.29 GHz (10.75%) at the dual bands. The maximum gains were 7.9 dBi and 6.97 dBi, and greater than 92% efficiency was obtained over the dual-band. From the results extracted from the proposed antenna, it was found that the antenna is capable of covering the 5G NR n257/n261/n259 and n260 bands with significant bandwidth, gain, isolation, ECC, DG, TARC, Multiplexing Efficiency, CCL MEG, and radiation efficiency. Thus, the antenna can be considered a potential contender for 5G millimeter wave wireless communication systems.
The demand for high data rate, good channel capacity, and reliability is always the primary area of concern in the modern era of wireless communication systems. The 5G standards have the fortitude to bring about rapid data transfer speeds, instantaneous connectivity, large data capacities, and minimal latency. In this paper, a novel quadrangular slotted defected ground structure (QSDGS) that incorporates a microstrip wide band antenna (WMA) was proposed for 5G n46/n47/n79 and n102 band applications. The DGS was represented on the ground plane by four rectangular looped slots. An inset feeding technique was employed on this slotted patch antenna. This DGS loaded patch antenna structure was mounted on an RT Duriod 5880 (εr = 2.2, loss tangent = 0.0009) with dimensions of 33 x 29 x 1.5 mm3 (0.44λ x 0.38λ x 0.02λ, where `λ' is calculated at lowest operating wavelength). This embedded antenna radiating structure resonated in a wide band ranging from 4.03 GHz to 6.32 GHz giving an impedance bandwidth of 2.3 GHz (50%), with a centre frequency of 4.44 GHz. The maximum gain was 4.7 dBi, and greater than 75% efficiency was obtained over the wide band. From the results extracted from the proposed antenna, it was found that the antenna was capable of covering the 5G NR n46/n47/n79 and n102 bands with significant bandwidth, gain, and efficiency. Thus, the antenna can be considered a potential contender for 5G mid-band wireless communication systems.
In this paper, we present a new numerical anisotropy optimization method for the three-dimensional (3D) radial point interpolation method (RPIM) in lossy media. Instead of evaluating the parameters of the artificial anisotropy or the scaling factors along the selected axes, as it is usually done in classical optimization algorithms, once the analytical expressions of these parameters have been determined, they are assigned at each node through their shape functions. By adaptive factor, we mean that its value varies in such a way to cancel the discrepancy between numerical and exact wavenumbers at each node. Doing such optimization at each node is indeed being possible during the calculation of these parameters by the RPIM dispersion relation. Therefore the numerical anisotropy is no longer optimized by averaging over the entire Cartesian grid but in each node direction. The RPIM numerical anisotropy adaptive optimization method (AOM) in lossy media is presented, and the theoretical adaptive factors are given as functions of nodes positions. Our results show that the numerical errors of the dispersion and the anisotropy are considerably reduced, after being optimized with the AOM. The proposed AOM scheme is applied for a 3D rectangular cavity in order to test its validity and evaluate the accuracy of the numerical results of our approach.
Two different MIMO antennas configurations are proposed in this paper for operation around 30 GHz with a bandwidth of 0.8 GHz. The proposed configurations are applicable in 5G, 6G and radar systems in Ka-band systems. Each of the proposed configurations consists of four identical rectangular elements where each element is connected to an impedance transformer for impedance mismatch improvement. Due to the close existence of antenna elements, mutual coupling can seriously degrade the gain, signal to noise ratio, matching characteristics, and efficiency of the MIMO antenna systems. To overcome performance degradation, several techniques such as Curved Edges (CE), Defected Ground Structure (DGS), and Band Gap Structure (BGS) are implemented. Simulation was carried out using the commercial Computer Simulation Technology (CST) and High Frequency Structure Simulation Software (HFSS). Prototypes are fabricated and measured. The experimental results show good agreement with the simulated ones. Improvement in the mutual coupling value from -21.4 dB to -27.2 dB also proves the practicality of this design.
This paper presents the deep learning assisted distorted Born iterative method (DBIM) for permittivity reconstruction of dielectric objects. The inefficiency of DBIM to reconstruct strong scatterers can be overcome if it is supported with Convolutional Neural Network (CNN). A novel approach, cascaded CNN is used to obtain a fine resolution estimate of the permittivity distribution. The CNN is trained using images consisting of MNIST digits, letters, and circular objects. The proposed model is tested on synthetic data with a different signal-to-noise ratio (SNR) and various contrast profiles. Thereafter, it is verified by means of experimental data provided by the Institute of Fresnel, France. Reconstruction results show that the proposed inversion method outperforms the conventional DBIM method in terms of accuracy as well as convergence rate.
In this study, a novel Switched Beam Antenna (SBA) system is proposed and experimentally validated for C-Band applications. The system is made up of a 4 × 4 Butler matrix, whose outputs are connected to four square-looped radiator antenna elements. The originality of the proposed work depends on the construction of a miniaturized beamforming network with minimal complexity, low loss, and low expense. Moreover, designing a system with a broad frequency range enables its use in a variety of applications. Miniaturization is achieved by eliminating the crossover and integrating the 45˚ shifter into the 90˚ hybrid coupler, as well as tilting the antenna array (i.e., making the Butler matrix output and the feed line of the antenna element orthogonal). The simulated results of the phase difference between the suggested Butler matrix outputs closely match the -45˚-135˚ theoretical calculations. The SBA measured results show a wide bandwidth and low insertion loss of 63.64% (4.21-8.14 GHz) and -4.89 dB, respectively. Four orthogonal beams are produced by the proposed structure's input ports 1-4 when they are excited. These beams are aligned at angles of -10˚, 60˚, -60˚, and 10˚ at 5.7 GHz.
The bodies of platform staff workers in high-speed railway stations absorb induction electric field when exposed to the electric field environment of contact wires with 25 kV high-voltages. To analyze the safety of electromagnetic exposure of the station platform staff workers with different numbers of tracks, this paper establishes a model with 6 tracks, 2 platforms, and 4 staff workers on the platform simulating the actual situation. It then analyzes the distribution of induction electric field present in their human body tissues, which in the electric field environment is generated by the high voltages of the contact wires of 1 track, 3 tracks, 6 tracks, respectively. Calculation results show that the maximum induction electric field of staff worker on the platform with different track numbers appears at the scalp, and the electric field intensity levels in the skull and brain are relatively small. For example, on the two platforms with 6 tracks, the maximum induction electric field of the staff worker is found in the scalp, and the values are 58.86 times and 1688.52 times of those of the skull and brain, respectively. For the staff worker at the safety white line, the maximum induction electric field in a human central nervous system is 0.61 mV/m, which is far less than the basic limit of 100 mV/m occupational exposure in the International Commission on Non-Ionizing Radiation Protection (ICNIRP) guidelines. With the increase in the number of tracks, the maximum induction electric field of the staff also increases correspondingly at the same position. Research results can provide data reference for the formulation of electromagnetic protection and standards for high-speed railway platform staff workers.
A flexible, planar electrically small antenna (ESA) with omni directional radiation pattern is designed and fabricated for GPS and WLAN applications resonating at 1.5 GHz and 3.7 GHz. The design consists of a circular loop attached with 3 rectangular bars, and it is fed by a 50 Ω feed line. The circular loop in the antenna provides impedance matching. Generally, these electrically small antennas have narrow bandwidth. Here the antenna is fabricated on a polyimide substrate having a thickness of 0.1 mm, εr of 3.4 mm, and it occupies a size of 38 mm x 34 mm. Electrically small antenna is designed at 1.5 GHz, 3.7 GHz, and the parameters that are measured are S11, VSWR, ka values, quality factor, and radiation patterns.
In this paper, a low profile horizontally polarized wideband omnidirectional antenna is presented, which consists of a simple single-layer dielectric substrate planar printing structure. The bottom of the substrate is loaded with six Vivaldi slits to achieve omnidirectional radiation. An equal-amplitude 1:6 power-division network is printed on the top of the substrate to provide a uniform feed. In addition, rectangular slots etched on each radiation element conduce to the enhancement of high-frequency gain and improvement of impedance matching. The antenna has 58.8% impedance bandwidth (2.8-5.13 GHz, VSWR<2) and low profile height of 0.009λmin, and it is convenient to fix under the ceiling of buildings and could radiate well in indoor place. The radiation mode in the whole operating frequency band is stable, and the cross-polarization is less than -20 dB, which completely covers the 5G NR-n77/78/79 band.
The results of the development of an approximate approach for describing structured waveguides, which can be considered as an analogue of the WKB method, are presented. This approach gives possibility to divide the electromagnetic field in structured waveguides with slow varying geometry into forward and backward components and simplify the analysis of the field characteristics, especially the phase distribution. The accuracy of this method was estimated by comparing the solution of the approximate system of equations with the solution of the general system of equations. For this, a special code was written that combines the proposed approach with the more accurate one developed earlier. For the case of fast damping of evanescent waves, a simple solution of the matrix equations is obtained. Based on this approach, the possibility of correcting the phase distribution in a chain of coupled resonators has been studied.