Mutual Coupling Effects Research Articles

Influence of Random Errors in Element Positions on Performance of Antenna Arrays Considering Mutual Coupling Effect

In engineering, random errors in radiating element positions caused by the manufacturing and assembly process could lead to degradation of the radiation performance of an antenna array. In order to accurately evaluate the deterioration of the antenna performance in the design phase, a statistical analysis method considering the mutual coupling effect between array elements is developed herein. The mutual coupling effect is described in terms of modal coupling and is governed by the modal coupling equilibrium equation. The statistical characteristics such as the mean and variance of the gain pattern are obtained based on the second-order Taylor expansion, and the expansion coefficients are obtained by the adjoint method. The correctness and effectiveness of the proposed method are verified through a comparison with the standard Monte Carlo method.

Second-Order Cone Programming (SOCP) Model for Three Phase Optimal Power Flow (OPF) in Active Distribution Networks

With the high penetration of distributed generations (DGs), modern distribution systems require novel and efficient optimal power flow (OPF) models. This paper proposes a second-order cone programming (SOCP) based AC-OPF model for three-phase radial power distribution networks. Mutual coupling effects are generally ignored in the existing multi-phase SOCP AC-OPF models. To overcome this critical issue, the proposed SOCP-OPF model introduces a coupling coefficient for the mutual coupling effects on the three-phase unbalanced lines. The derivation of the coupling coefficients has been illustrated with the required proof that the relaxation is tight and the solution from the proposed OPF model is optimal for an unbalanced multi-phase distribution network. The SOCP-OPF model is evaluated on several IEEE standard distribution networks without and with high penetration of Distributed Energy Resources (DERs). It has been shown that the proposed OPF model provides an optimal global solution for convex objective functions. Also, this OPF model is scalable and computationally efficient compared to Nonlinear Programming (NLP) and other convex OPF models.

Antenna Array with Low Side Lobe Levels for MIMO Applications

Abstract: To design a single element microstrip patch antenna at a frequency of 4 GHz. A uniform planar array with 4 patch elements is designed. A non uniform planar array is designed to overcome the mutual coupling effect. Simulation of the designed uniform planar array and non uniform planar array antenna array is performed on HFSS tools. A single microstrip feed patch antenna element is designed at a frequency of 4 GHz. The substrate material used is Rogers 6002. A 2*2 array is designed by using 4 similar patch elements. The proposed model has dimensions of the substrate as 58mm x 68mm, the dimensions of the patch is 20mm x 22mm. For the proposed model slots are added to each patch with the dimensions 5mm x 1mm. The substrate material used is FR4 epoxy. It is further improved by changing the dielectric material variations, slot arm length variations, slot arm thickness variations.

A Novel Unit Classification Method for Fast and Accurate Calculation of Radiation Patterns

This paper proposes a novel unit classification technique to enhance the accuracy of the conventional pattern multiplication method by taking the mutual coupling effect and edge effect into consideration. The proposed technique classifies antenna elements into different groups based on their positions in arrays, specifically corner, edge, and inner groups. By simulating the radiation patterns of antenna elements with different boundary conditions, the pattern multiplication method is then used to calculate the radiation pattern of the antenna array based on the simulated results. Several numerical examples, including a square array, a hexagonal array, and a phased array, are provided to validate the effectiveness of the proposed method. The numerical results demonstrate that the proposed method not only reduces the computational time and memory usage but also significantly improves the accuracy. The proposed method provides a powerful tool for synthesizing and predicting the radiation pattern of array antennas and offers new avenues for optimizing array antennas and phased array antennas.

Joint Range and Angle Estimation by FDA-MIMO Radar With Unknown Mutual Coupling

Frequency diverse array-multiple-input multiple-output (FDA-MIMO) radar is characterized by a range-angle-dependent transmit antenna beampattern, where both range and angle of the target can be jointly estimated. However, the performance of existing estimation algorithms degrades in the presence of mutual coupling effect. To overcome this drawback, this paper deals with the problem of joint range and angle estimation by FDA-MIMO radar with unknown mutual coupling. At the design stage, the mutual coupling matrices (MCM) are constructed in both transmit and receive arrays, exploiting the banded symmetric Toeplitz structure, where the mutual coupling effect is eliminated by transforming the MCM into a diagonal matrix with a selection matrix. Subsequently, the range ambiguity is resolved by setting two linear coprime frequency increments, which locates the true target at the overlap of the peaks corresponding to the two spatial spectra. Furthermore, to reduce the computational cost resulted from the two-dimensional (2-D) grid search, an iterative procedure based on the coordinate descent (CD) algorithm is considered by alternating between the optimization over one variable keeping the other fixed. At the analysis stage, the closed-form solutions of the mutual coupling coefficients are given by utilizing the estimated range and angle. Moreover, a comparison in terms of estimation performance in different coupling scenarios is carried out, where the Cramér-Rao lower bound is provided as the benchmark. Numerical results verify the effectiveness of the considered estimation strategy in multiple simulated scenarios.

Analysis and Compensation of Deformed Antenna Arrays Based on Infinitesimal Dipole Model

This paper presents a new method for analyzing the electrical performance of deformable antenna arrays based on the infinitesimal dipole model (IDM). The surface of the antenna array will inevitably deform during use. However, in practical engineering applications, it is time-consuming and expensive to use conventional methods to analyze the electrical performance of deformed antenna arrays. In this method, the deformation of the antenna is transformed into the translation and rotation of a group of infinitesimal dipoles by IDM equivalent. The mutual admittance of the deformed elements is calculated to consider the influence of the deformation and the mutual coupling effect between the radiating elements. Based on this, the influence of the deformation of the antenna structure can be quickly and effectively evaluated. Finally, the deformed antenna array is compensated based on the least squares error (LSE) method, and its correctness and feasibility are verified by a numerical example.

High-Resolution Parameter Estimation for Wideband Radio Channel Sounding

Multidimensional channel sounding measures the geometrical structure of mobile radio propagation. The parameters of a multipath data model in terms of directions, time-of-flight and Doppler shift are estimated from observations in frequency, time and space. A maximum likelihood estimation framework allows joint high-resolution in all dimensions. The prerequisite for this is an appropriate parametric data model that represents the multipath propagation correctly. At the same time, a device data model is necessary that typically results from calibration measurements. The used model should be as simple as possible since its structure has a considerable effect on the estimation effort. For instance, the inherent effort in parameter search is reduced if the influence of the parameters is kept independent. Therefore, the data model is characterized by several approximations. The most important is the “narrowband assumption” which assumes a low relative bandwidth and also avoids considering any frequency response in magnitude and phase. We extend the well-known multidimensional RIMAX parameter estimation framework by including proper frequency responses. The advantage reveals itself with high bandwidth in the mmWave and sub-THz range. It allows for a more realistic modeling of antenna arrays, it breaks with the usual narrowband model and allows a better modeling of mutual coupling and time delay effects. If the interacting object extends over several delay bins (hence an extended target in radar terminology) we propose a model that assigns a short delay spread, respectively a frequency response to the propagation path that associates it to the respective object. We verify the validity of the device model by numerical experiments on simulated and measured antenna data and compare it to RIMAX. Additionally, we use synthetic data based on ray-tracing results and measurements both ranging from 27.0GHz to 33.0GHz with known ground truth information and show that the proposed estimator delivers better performance for higher relative bandwidths than the conventional RIMAX implementation.

A dilating and embedding scheme for constructing sparse MIMO radar array

AbstractIn this letter, a dilating and embedding scheme for constructing sparse multiple‐input and multiple‐output radar arrays is addressed, which seeks to increase the uniform degrees of freedom (uDOFs) and reduce the mutual coupling effects for a given number of transmitters and receivers (Tx/Rx). According to this scheme, a dilated maximum inter‐element spacing constraint (MISC) array with an embedded thinned coprime array in the collocated MIMO radar for DOA estimation is proposed. Theoretical analysis shows that the proposed array can provide higher uDOFs and is robust in a scenario with heavy levels of mutual coupling. Numerical simulations are conducted to validate its aforementioned advantages in line with the design scheme.

Modeling guyed towers of transmission lines in the assessment of backflashover occurrence

This paper evaluates the modeling of guyed towers of transmission lines in EMT-type programs to assess the backflashover occurrence of transmission lines and proposes a new modeling approach to be applied for this kind of towers. Two approaches to model the guyed towers by the revised Jordan model were evaluated: (i) the approach of CIGRE Brochure 63 that suggests representing the tower surge impedance as the parallel of the surge impedances of the mast and the guyed wires, ignoring the mutual coupling among them, and (ii) a new approach assuming the surge impedance of all the conductors in the tower section, guyed and mast conductors, including their mutual coupling effect. The evaluations considered the results provided by the Hybrid Electromagnetic Model (HEM) as reference for assessing the quality of the approaches. The approach (i) provided results of lightning overvoltage significantly lower than the reference, HEM model, leading to an underestimation of the probability of backflashover of the line. On the other hand, the approach (ii) was responsible for the results closest to those provided by HEM, indicating its quality, and the recommendation of applying this proposed approach for modeling guyed towers in the evaluations of backflashover occurrence.

Optimal sparse linear array design with reduced mutual coupling effect

Sparse linear arrays (SLAs) provide a high number of degrees of freedom (DOF) and reduce the mutual coupling effect between sensors of the array. Many design methods for SLAs have been proposed in the last two decades but most of the existing SLA design methods fail to achieve minimum number of sensors for a desired DOF. In this paper, a design method is proposed which utilizes the branch and bound (B&B) optimization algorithm to give a SLA with the desired DOF and minimum number of physical sensors. The proposed SLA design method is obtained by generalizing the minimum sensor array (MSA) design method which is recently proposed in the literature. This generalized method provides the same DOF as the MSA method but with a smaller number of physical sensors. In addition, a version of this design method is proposed which provides more robustness against mutual coupling effect between the sensors of the array. Simulation results demonstrate the superiority of the performance of the SLAs obtained with the proposed method over the arrays obtained with the MSA method and also over the other existing SLAs.

3D Printed SnS2/SnS-Based Nanocomposite Hydrogel as a Photoenhanced Triboelectric Nanogenerator

Recent advancements in printing technologies have led to new fabrication techniques for the development of various flexible, compact, wearable, and portable energy harvesters and self-powered devices. In particular, the three-dimensional printing (3DP) technology for a nanogenerator has become advantageous due to its low cost, simplicity, and high precision in fabricating complicated structures. Therefore, we report a 3DP-based photoinduced triboelectric nanogenerator (PTNG) fabrication, a hybrid version of a conventional triboelectric nanogenerator. Here, a 3D printed poly(vinyl alcohol) (PVA) nanocomposite hydrogel (3DPH) with photoactive SnS2/SnS nanoflakes is used as a tribo-positive material and copper foil as a tribo-negative material for PTNG application. Under light illumination, the as-fabricated PTNG with an optimized weight percentage of SnS2/SnS displays the open-circuit voltage (Voc) enhancement from 29 to 37.5 V and short-circuit current (Isc) enhancement from 1.23 to 1.58 μA. In addition, the power density of the device is observed at 5.4 μW/cm2 under illumination conditions at the external load of 60 MΩ. This enhanced performance of the as-fabricated PTNG is attributed to the mutual coupling effect and improved interfacial interactions between the SnS2/SnS nanoflakes and PVA under the influence of light illumination, leading to a charge-trapping mechanism. The outstanding performance and stability of the as-fabricated PTNG surpassing all similar recent reports, establish it as an effective hybrid platform for constructing multifunctional self-powered devices.

Design of Ultrawideband RCS Reduction Metasurface Using Space Mapping and Phase Cancellation

An efficient optimizing method of ultra-wideband radar cross-section (RCS) reduction metasurface involve unit amplitude differences and mutual coupling effects is proposed in the letter. Multiple unit phase cancellation was used to broaden RCS-reduction bandwidth. The genetic algorithm was utilized to further design and select the optimal combination from various tiles. To improve the optimization efficiency and accuracy, the space mapping (SM) technique was exploited to refine the design process, which involves the interactions of scattering fields among tiles and subarrays in wideband. Meanwhile, the constraint of wide-angle oblique incidences is also considered in wideband low RCS design. An ultra-wideband RCS reduction checkboard meatsurface can be accomplished by fast optimization of low-cost coarse model and few parameter mapping courses between fine and coarse model. A 10dB RCS reduction for HH and VV polarizations under normal and other oblique incidence angles can be achieved from 5 to 40 GHz. Good agreements between simulation and experiment results are obtained.

Robust Block Sparse Beamforming for Strictly Non-Circular Signals and Unknown Array Mutual Coupling

Widely linear beamformers (WLBs) can greatly outperform the traditional adaptive beamformers. However, the performance of WLBs is extremely susceptible to the unknown mutual coupling (MC) effects caused by the imperfectly calibrated antennas array. In this brief, we propose a block sparse representation scheme and design a robust WLB for strictly non-circular (SNC) signals to mitigate the unknown MC mismatch. We use the structural characteristics of the steering vector under MC, and derive a new augmented formulation for the observed signals which takes into account the MC mismatches. We solve a block sparse optimization problem in order to estimate the directions of illuminating signals allowing us to reconstruct the augmented interference-plus-noise covariance matrix (AINCM). We then propose to estimate the augmented desired signal steering vector using the augmented subspace projection method. Our proposed robust WLB not only avoids estimating the MC coefficients, but also prevents the signal cancellation phenomenon from reconstructing the AINCM. Our simulation results demonstrate that the proposed WLB is effective for the SNC signals, outperforms the existing methods, and is robust against unknown MC and look direction mismatches.

A novel helical antenna for high-power design in X-band

This paper describes a novel helical antenna for high-power design in X-band. Based on the advantages of miniaturization, high efficiency, and low-profile from helical antenna, firstly, by optimizing the primary parameters, the helical antenna obtains a significant axial ratio bandwidth and operational bandwidth in X-band. Then in array antenna design, metal frames are introduced to decrease the mutual coupling effects, reducing the lower-impedance bandwidth decrease from 9.77 GHz to 8.08 GHz. Meanwhile, to further realize high-power design, a novel curved feed structure is employed to boost the power capacity increase from 31.1KW to 43.8KW. The measured results show that the proposed helical antenna has an operating bandwidth across X-band (reflection coefficient < −10 dB), and the max power capacity of the antenna finally ascends to 43.8 kW.

Antennas for low-frequency radio telescope of SKA

The low-frequency radio telescope of the Square Kilometre Array (SKA) is being built by the international radio astronomical community to (i) have orders of magnitude higher sensitivity and (ii) be able to map the sky several hundred times faster, than any other existing facilities over the frequency range of 50–350 MHz. The sensitivity of a radio telescope array is in general, dependent upon the number of electromagnetic sensors used to receive the sky signal. The total number of them is further constrained by the effects of mutual coupling between the sensor elements, allowable grating lobes in their radiation patterns, etc. The operating frequency band is governed by the desired spatial and spectral responses, acceptable sidelobe and backlobe levels, radiation efficiency, polarization purity and calibratability of sensors’ response. This paper presents a brief review of several broadband antennas considered as potential candidates by various engineering groups across the globe, for the low-frequency radio telescope of SKA covering the frequency range of 50–350 MHz, on the basis of their suitability for conducting primary scientific objectives.

Application of KNN for Linear Array Pattern Prediction Based on the Active Element Pattern Method

In this paper, a machine learning-based algorithm, K-Nearest Neighbor (KNN), is employed to predict the actual patterns of the linear arrays with arbitrary positions and varied element numbers. Based on the assumption that the active element pattern (AEP) is only susceptible to adjacent elements, the AEP of each element is predicted according to its subarray geometry features. And the array pattern is calculated correspondingly. To verify the validity of the method, the proposed methodology was employed to predict the patterns in several array synthesis cases using a dataset constructed from a series of full-wave simulated 17-element microstrip antenna arrays. Numerical results demonstrate that the proposed method is capable of predicting the pattern of arrays with arbitrary geometries and varied element numbers ranging from 7 to 127 with promising precision, which indicates that the proposed method is a feasible and effective array pattern calculation approach and applicable for all linear array synthesis problems with position optimization ability and mutual coupling effect considered.

Bidirectional Hybrid X Shape FCL in HVdc System With Multifunctional Feature

Bidirectional fault issue is common and serious in HVDC system and it cannot be handled by unidirectional fault current limiter (FCL). The novel contribution of this paper is that it proposes a hybrid X shape FCL (HXFCL) with bidirectional fault limiting, fast breaking and power flow adjusting capabilities. The HXFCL adopts the mutual inductance coupling effect of limiting magnetic modules and uses the full/semi control power electronic devices group. By working with the system fault protection signal and breaking part of the DC circuit breaker, the HXFCL can alter its device status and implement different functions with variable reactance. This article presents general topology of the HXFCL and gives analytical and optimization work of magnetic part. Meanwhile, electrical feature, control strategy, complete functions and detailed performance comparison of the proposed HXFCL were performed. Simulations and experiments verify that the proposed HXFCL can work under multiple occasions. The fault limiting performance can be significantly improved, while the breaking requirements and reacting time can be significantly reduced.

Physics‐based iterative scheme for computing antenna array embedded element patterns

AbstractRigorously accounting for mutual coupling effects in antenna array synthesis, generally requires that embedded element patterns (EEPs) be determined. The method of moments (MoM) is typically used. Multiple linear system solutions are required, corresponding to every excitation vector associated with an EEP. This paper presents the direct coupling technique (DCT) to obtain the MoM solution for arrays with disjoint elements, by iteratively solving a series of localized subproblems, one associated with each array element. It utilizes a physics‐based, direct‐coupling approximation to incorporate global coupling into the local problems. Local matrices do not change between iterations or with excitation vectors, hence they can be inverted as a preprocessing step, allowing for efficient solution of multiple excitation configurations. Numerical results demonstrate rapid convergence. The convergence rate can be controlled via local problem domain sizing. Since the DCT is ideally suited to parallelization, it is applicable to very large arrays.

Inflationary magnetogenesis of primordial magnetic fields with multiple vector fields

In this paper, we discussed the multiple vector fields during the inflation era and the inflationary magnetogenesis with multiple vector fields. Instead of a single coupling function in single vector field models, the coupling matrix between vector fields and scalar field which drive the inflation is introduced. The dynamical equations for multiple vector fields are obtained and applied to the inflation era. We discussed three cases for the double-field model. In the no mutual-coupling case, one can find that both electric and magnetic spectrum can be scale-invariant at the end of inflation, meanwhile, the strong coupling problem can be avoided. The effect of mutual coupling between different vector fields is also discussed. We found that weak mutual coupling can lead to a slightly blue spectrum of the magnetic field. On the other hand, in the strong mutual-coupling case, the scale-invariant magnetic spectrum can also be obtained but the energy density of electromagnetic fields either leads to the backreaction problem or is diluted by inflation.

Design of an applied method with graphite structure for suppression of surface electromagnetic waves between array antennas

In this study, a method of combining graphite structure and electromagnetic bandgap to reduce the mutual coupling of electromagnetic waves in array antennas is proposed. This structure is designed according to the special physical properties of graphite for the emission of electromagnetic waves, transmission theory, as well as the inductance and capacitive properties of the electromagnetic bandgap structure to dissipate surface currents. The proposed multi-input and multi-output (MIMO) antenna was designed and measured with two radiating elements on a substrate. The results show that the effects of mutual coupling between radiating elements are reduced by 30 dB at the operating frequency of 3.34 GHz. By placing this structure, all antenna components, including gain, patterns, and radiation efficiency, are improved. Calculations showed that antenna components: gain and antenna radiation efficiency increased by 1.2 dB and nearly 24%, respectively. To confirm the good performance of the graphite structure, all components of the MIMO antenna, including the envelope correlation coefficient, diversity gain, mean effective gain, channel capacity loss, and total active reflection coefficient, were investigated. The results showed the desired values, which indicate the very good performance of the graphite structure on all the basic characteristics of the antenna.