The role of the source geometry is investigated within the realm of inverse source problems. In order to examine the properties of the far zone radiation operator of some 2D curved sources its Singular Value Decomposition (SVD) is studied, either analytically, when possible, or numerically. This allows to evaluate the number of independent pieces of information, i.e. the number of degrees of freedom (NDF), of the source and to point out the set of far zone fields corresponding to stable solutions of the inverse problem. In particular, upper bounds for the NDF are obtained by exploiting Fourier series representations of the singular functions. Both curved (i.e. circumference and arc of circumference) and rectilinear geometries are considered, pointing out the role of limited angular observation domains. Moreover, in order to obtain some clues about the resolution achievable in the inverse source problem, a point-spread function analysis is performed. The latter reveals a spatially variant resolution for limited angular observation domains. The practical relevance ofthese results is highlighted with numerical examples of array diagnostics.
We numerically demonstrate that an electromagnetically induced transparency (EIT) effect can be achieved in an all-dielectric metamaterial, whose micro unit consists of two cylindrical through-hole cubes (CTCs). Two CTCs produce electric and magnetic Mie resonances in the vicinity of 6.2 GHz, respectively. Specially, the appropriate control on the interaction between two Mie resonances can lead to destructive interference of scattering fields, and thus the EIT effect with low loss and high transmission can be achieved. The influences of key parameters of all-dielectric metamaterial on its EIT effects are also investigated. In addition, the slow wave property of proposed structure is verified by computing the group delay, and the superiority of CTC is discussed. Such an all-dielectric metamaterial may have potential applications in areas such as low loss slow wave devices and high sensitivity sensors.
Two mu-zero resonance (MZR) resonators are etched in the patch of a microstrip antenna. The two MZR resonators generate two new resonances. As the MZR resonances are lower than the microstrip antenna resonance and the resonances merge with each other, size reduction and bandwidth enhancement were obtained. A prototype was designed and measured. The measured impedance bandwidth increased from 640 MHz (5.31-5.95 GHz, 11.33%) of the referenced microstrip antenna (RMA) to 940 MHz (4.99-5.93 GHz, 17.22%) of the proposed MZR loaded microstrip antenna (MZR-MA). Moreover, the patch size is decreased from 0.354λl × 0.283λl of the RMA to 0.332 λl × 0.266λl of the MZR-MA, and unidirectional radiation patterns are obtained for the microstrip patch and MZR resonances. A microstrip line based model was built to analyze the MZR resonators.
This paper presents an ease of dual-mode diplexer with high signal isolation based on amplitude and phase cancellation technique. The dual-mode structure enables a compact and easy asymmetrical frequency response which also requires considerable attenuation between the proximity in frequency of the transmitter and that of the receiver. Two back-to back dual-mode three-port diplexers and a 180˚ phase shifter are easily employed to construct the proposed device, which are combined to form a four-port dual-mode diplexer. A 180˚ phase shift in one branch can be achieved by delayed transmission line. The simulated and measured four-port dual-mode diplexers are designed at the operational frequency of Tx/Rx at 1.95 GHz and 2.14 GHz, respectively. The measured results of Tx/Rx dual-mode diplexer devices are presented of 48.5 dB Tx/Rx isolation. This four-port dual-mode diplexer achieves the isolation (S32) more than 21.5 dB compared with a conventional three-port dual-mode diplexer.
A miniaturized U-Shape patch sensor (15 mm×15 mm) was designed at dual resonating frequencies (fr) 5.2 GHz and 6.8 GHz). The proposed design printed on FR4 material with a thickness of 1.676 mm and relative permittivity 4.4. To simulate the performances of the proposed design, the CST Microwave Studio (CST MWS) was used. The reflection coefficient of U-Shape patch sensor was measured. Basmati rice was investigated, and bulk density was increased with increase of moisture content, hence varied from 554.3 to 591 kg/m3. It has the longest average rice length (L) 7.2 mm, average width (W) 1.61 mm, and L/W ratio 4.47. The percentage of moisture was varied from 10.12% to 20.35% calculated on a wet weight basis. The lowest mean relative error (MRE) determined between predicted moisture content (PMC) and actual moisture content (AMC) was 0.55% at dual frequencies.
This article presents the design and analysis of a dual-band antenna with circular polarization for ISM and WLAN band applications. The proposed antenna operates at two frequencies ranging from 2.1-3.1 GHz and 4.4-7.7 GHz with resonating frequencies at 2.45 GHz industrial, scientific and medical band (ISM) and 5.8 GHz wireless local area network band (WLAN). The antenna is fed by coplanar waveguide feeding (CPW) with an asymmetric ground structure, and the radiating element consists of 24 spokes in the design. The current antenna providing the impedance bandwidths of 38.4% and 49% at two operating bands. The proposed antenna exhibiting circular polarisation with 3 dB axial ratio bandwidth of 150 MHz at 2.33-2.48 GHz and 1600 MHz at 5.14-6.74 GHz. The designed antenna is fabricated on an RT Duroid 5880 substrate with dimensions of 40 x 28 x 0.4 mm3. The intension behind the design of this antenna is to use it for wearable applications in conformal nature with low specific absorption rate (SAR). The SAR values observed at two operating frequencies are 1.09 W/Kg and 1.47 W/Kg, respectively. The placement and radiation characteristics analysis is done with Ansys Savant tool, and the subsequent measured results provide good correlation with simulation results.
A novel cross polarized compact antenna system is proposed for Ultra Wide Band communications. It also covers the sub-6 GHz band for initial 5G launch. The overall antenna system is a distinctive combination of Multiple Input Multiple Output (MIMO) antenna system covering radio frequency (RF) band starting from 2 GHz to 12 GHz. This MIMO system consists of two F-shaped monopoles with slotted fractured ground planes. The two antennas are fabricated back to back with 90 degree difference. The overall volume of the MIMO antenna system is 14 mm × 14 mm × 0.25 mm. Due to its very compact design, it is suitable for mobile phones and other hand-held devices. The peak measured gain has been achieved as 4.8 dB, and the measured far field patterns are nearly isotropic. Envelope Correlation Coefficient (ECC) and Gain Diversity are presented for the proposed MIMO antenna system.
The technique to retrieve the microwave permeability of metals from the measured constitutive parameters of composites with fine powder of these metals is developed. The technique is based on the modified Sihvola mixing rule and describes a wide range of contrasts in the component susceptibility, accounts for both the inclusion shape and the percolation threshold. These parameters are related to the Bergman-Milton shape-distribution width and to composite structure. The technique is applied to retrieve the microwave permeability of nickel. The metal permeability is calculated from the measured permittivity and permeability of paraffin-bound composites filled with nickel flakes or spheres with account for skinning in conducting inclusions. The measurements are performed using the transmission coaxial-cell in the frequency range up to 15 GHz. The effects of filling factor, inclusion shape and size on the retrieved permeability spectra are analyzed. The permeability retrieval procedure is based on parameter fitting of the selected mixing model for the measured permittivity and permeability data. The retrieved permeability is close to the data available from archived literature sources that are obtained with thick nickel wires and foils.
In this paper, a dual-band stub (DBS) comprising one lumped kernel circuit unit cell (KCUC) and two distributed uniform transmission lines is presented. An odd-even mode resonant frequency ratio (OEMRFR) is introduced, which can determine all the element values in the DBS circuit model. Its phase and impedance bandwidth properties are extracted based on the image parameter theory. By adjusting the OEMRFR value, the second working bandwidth and structural size can be controlled simultaneously. On the other hand, the input and output space mapping (IOSM) is exploited to realize a planar microstrip DBS by transferring the lumped KCUC into a quasi-lumped formation. The established ISOM design process is fully automated and can generate the finalized DBS layout with just a few full-wave simulations. A DBS operative at WLAN dual frequencies of 2.4/5.8 GHz with extended bandwidth is designed as an example. Good agreement between the measured and simulated results justifies both the extracted dual-band performance of the proposed DBS and its customized IOSM design process.
The incorporation of Electromagnetic Band Gap (EBG) unit cells, a type of metamaterials, with a dual band array antenna is proposed. By configuring the band gap of EBG cells accordingly, the pattern of the array antenna is successfully reconfigured at lower band of 2.4 GHz while maintaining the pattern at higher band of 5.8 GHz. Three pattern directions have been achieved: initial radiation pattern, 349-degree shift and 11-degree shift of the H-field. The array antenna is also frequency reconfigurable by suppressing the radiation pattern of the antenna in four different EBG cells configurations. In pattern shifting mode, the realized gain of the antenna is satisfactorily maintained and is comparable with the standalone of dual band array antenna with the range of gains from 5.08 dBi to 6.14 dBi and 7.83 dBi at 5.8 GHz.
In this paper, the impact of decoupler type has been analysed on the performance of planar inverted-F antenna (PIFA)-based multiple-input multiple-output (MIMO) antenna. A T-type and a loop-type decoupler have been employed for the isolation of the MIMO antennas, and the performances of the two cases have been compared. The decouplers have been selected based on their different coupling mechanisms with the dominant ground mode. The antennas have been designed for the ground configuration of a USB dongle operating at 2.45 GHz band. Characteristic mode analysis of the ground plane has been carried out, and the MIMO systems have been analysed based on the coupling among the antenna, decoupler and the dominant characteristic mode of the ground plane. It has been observed that the coupling between the decoupler and the ground mode significantly affects the radiation efficiency as well as the diversity performance of the MIMO antenna.
In this article, a couple of UWB antennas are presented. These antennas have the shape of two overlapped circles. The presented antennas are polarization diversity antennas with and without dual band reject filters. Measurements show that the antennas work well within the whole UWB. Antennas have practical reflection parameters S11 and S22 lower than -10 dB, practical coupling parameters S12 and S21 lower than -15 dB, an Envelope Correlation Coefficient lower than 0.015 and a diversity gain between 9.97 to 9.99 dB. Simulations of the antennas are done using the CST software.
This paper proposes a novel source reconstruction method (SRM) based on the convolutional neural network algorithm. The conventional SRM method usually requires the scattered field data oversampled compared to that of target object grids. To achieve higher accuracy, the conventional SRM numerical system is highly singular. To overcome these difficulties, we model the equivalent source reconstruction process using the machine learning. The equivalent sources of the target are constructed by a convolutional neural networks (ConvNets). It allows us to employless scattered field samples or radar cross section (RCS) data. And the ill-conditioned numerical system is effectively avoided. Numerical examples are provided to demonstrate the validity and accuracy of the proposed approach. Comparison with the traditional NN is also benchmarked. We further expand the proposed method into the direction of arrival (DOA) estimation to demonstrate the generality of the proposed procedure.
This paper addresses the problem of target detection in adaptive arrays in situations where only a small number of training samples is available. Within the framework of two-stage adaptive detection paradigm, the paper proposes a class of rapidly adaptive CFAR (Constant False Alarm Rate) detection algorithms, which are referred to as joint loaded persymmetric-Toeplitz adaptive matched filter (JLPT-AMF) detectors. A JLPT-AMF detector combines, using a joint detection rule, individual scalar CFAR decisions from two rapidly adaptive two-stage (TS) detectors: a TS TAMF detector and a TS LPAMF detector. The former is based on a TMI filter, which is an adaptive array filter employing a Toeplitz covariance matrix (CM) estimate inversion. The latter is based on an adaptive LPMI filter that uses diagonally loaded persymmetric CM estimate inversion. The proposed class of adaptive detectors may incorporate any rapidly adaptive TS TAMF and TS LPAMF detectors, which, in turn, may employ any scalar CFAR detection algorithms that satisfy an earlier derived linearity condition. The two-stage adaptive processing structure of the JLPT-AMF detectors ensures the CFAR property independently of the antenna array dimension M, the interference CM, and the number of training samples NCME to be used for estimating this CM. Moreover, the rapidly adaptive JLPT-AMF detectors exhibit highly reliable detection performances, which are robust to the angular separation between the sources, even when NCME is about m/2 ~ m, m is the number of interference sources. The robustness is analytically proven and verified with statistical simulations. For several representative scenarios when the interference CM has m dominant eigenvalues, comparative performance analysis for the proposed rapidly adaptive detectors is provided using Monte-Carlo simulations.
This paper, published on Progress In Electromagnetics Research M, Vol. 76, 65–74, 2018, was withdrawn on July 5, 2019, as per the authors' request.
In this paper a substrate integrated waveguide (SIW) quasi-elliptic filter with a controllable bandwidth is proposed. The quasi-elliptic filter response is caused by the cross coupling technique and a dual-mode resonance cavity. The dual-mode resonance cavity with TE101 and TE102 modes is used to generate the passband, and the cross coupling provides two signal transmission paths to produce transmission zeros (TZs). The bandwidth of the filter can be controlled by a pair of disturbing metallic via-holes. A quasi-elliptic filter with the center frequency of 11.03 GHz is designed, fabricated and measured. The experiment data agree well with the simulated ones.
Seawater conductivity is an important factor that affects the corrosion electric field of ship.Athree-dimensional boundary element method (3D-BEM) combined with nonlinear polarization curve was employed to investigate the influence of seawater conductivity on the corrosion electrostatic field. Numerical simulation results show that the electric field distribution is only slightly influenced by the conductivity.However, the intensity decreases with the increases of conductivity. The simulation results of the BEM model were compared with the results of the equivalent electric dipole model, and the results obtained by the two methods had high similarity, which demonstrated that the BEM model was effective. The former is a more convenient and concise modeling method that can better reflect the distribution characteristics of ship's corrosion electric field than the electric dipole model.
Performance improvement of couple silver (Ag) - gold (Au) based bimetallic surface plasmon resonance (SPR) sensor using a thin indium phosphide (InP) layer and an air gap layer is presented. Through detailed investigations quantitative insight into the dependence of different performance parameters including sensitivity factor (SF), sensor merit (SM), full width at half maximum (FWHM) and combined sensitivity factor (CSF) on stack structure, thickness and material parameters has been observed. Integration of thin InP layer on the metallic layer and inclusion of the air gap between glass prism and adsorption layer enhance both the sensitivity (70.90˚/RIU) and the CSF (372.8 RIU-1). Without InP layer the sensitivity is 65.66˚/RIU, and CSF is 178.5 RIU-1 whereas without the air gap the sensitivity is 66.29˚/RIU, and the CSF is 285.0 RIU-1. Compared to similar bimetallic SPR sensors that have been reported in recent literatures, sensitivity and overall figure of merit of the proposed sensor are far better. The presented biosensor's capability to detect the variation of 1/1000 of RIU of the sensing medium (corresponding to subtle concentration change of the analyte) has been demonstrated.
Aiming at problems that interpolated array has large amount of computation and high sensitivity to transformation angle and interpolated step, a new array extension algorithm which is symmetric extension steering vector is proposed. In this paper, two properties of the conjugate of received data and the source covariance matrix being a real diagonal matrix are exploited to extend the dimensions of the covariance matrix. However, the essence of this extension method is the symmetric extension of the steering vector. The high complexity and degradation of the performance of interpolated array beamforming caused by the sensitivity of angle and interpolated step are improved. Numerical simulations confirm the validity of the proposed algorithm. Compared with existing algorithms, the proposed algorithm is not affected by the angle range of transformation and interpolated step. Besides, the complexity of array extension using this proposed algorithm is much lower than the interpolated transformation method.
An improved matrix synthesis approach for inline filter is presented in this paper. Frequency-variant couplings (FVC) can generate and control multiple finite transmission zeros (TZs). As the resultant network only involves resonators cascaded one by one without any auxiliary elements (such as cross-coupled or extracted-pole structures), this paper provides the best optimizatised synthesis solution in configuration simplicity for narrowband filters based on genetic algorithm (GA) and solvopt optimization method. Compared with the conventional synthesis method for inline topology filters, the method presented in this paper has following advantages: First, it is unnecessary to consider both the couplings and capacitances of a traditional low-pass prototype. Second, there is no need to use similar transformation, and the adjacent FVCs can be implemented. Third, the approach presented can implement more TZs than the previous works. The maximum number of TZs can be as many as the filter order. Two examples with different topologies and specifications are synthesized to show the validation of the method presented in this paper.
Angular misalignment is an issue for many potential applications of wireless power transfer (WPT). It is necessary to keep coupling coefficient, especially the magnetic coupling to be insensitive to angular misalignment. This paper analyzes the coupling between the spiral resonators when one resonator rotates with respect to the other. The quantitative data of magnetic and electric coupling components as well as the total coupling coefficient in angular misalignments are presented. Furthermore, a 3D spiral resonator which is less sensitive to angular misalignment is proposed. The coupling when the 3D spiral rotates is studied and the results of analysis and experiment both show that the proposed 3D spiral resonator can keep coupling coefficient at a certain level under angular misalignment.