Problem Of Mutual Coupling Research Articles

Design of circular slots loaded MIMO antenna with DGS at 28 GHz for 5G wireless services

In this paper, a MIMO microstrip patch antenna with four radiating elements is designed and analyzed at 28 GHz. This paper addresses the problem of mutual coupling without adding a decoupling network. The decoupling method increases the complexity and volume of MIMO antennas. The CST Microwave simulator is used to simulate the MIMO antenna. The simulation and measurement results are compared to analyze the antenna's performance. The parameters of the MIMO patch antenna, including return loss, VSWR, gain, beam width, and radiation pattern, are evaluated at a center frequency of 28 GHz. The overall dimensions of the MIMO antenna are 60 × 42 × 1.6 mm3.An H-shaped slot is inserted in the middle of the ground plane to minimize mutual coupling among the radiating elements. The isolation amplitude between radiating elements is observed greater than 35 dB at 28 GHz frequency. A wide impedance bandwidth of 4 GHz (26.5 to 30.5) is achieved, by etching four small arcs into the patch’s corners. In this work, two circular slots are inserted on the radiating element to widen the bandwidth further by adjusting the surface current on each radiating patch. At the center frequency of 28 GHz, the Envelope Correlation Coefficient (ECC) is observed to be 0.0001, with a diversity gain of 10 dB. The antenna has a maximum radiation efficiency of 75% and a peak gain of 7.62 dB. This antenna can be used for 5G wireless services.

Design and Fabrication of a 2-Port Multiple Antenna System for mmWave Application

The next-generation wireless communication technology heading towards the mmWave band requires multiple antenna systems to achieve high diversity, high data rates, and reliability. The design of multiple antenna systems is always associated with the problem of mutual coupling between antenna elements. In order to achieve better system performance, the mutual coupling between the elements has to be minimized. This work basically aims to minimize the mutual interaction among the antenna elements. A 2-port multiple antenna system is presented, with the defected ground structure as a decoupling technique, in order to minimize the mutual coupling. The single microstrip patch antenna is initially designed to operate at 24 GHz; later, it is transformed into a 2-port multiple antenna system. The transformed 2-port multiple antenna is loaded with the defective ground structure. The designed antenna system is fabricated, and practical measurements are carried out. The isolation achieved with defective ground structure through simulation is −27dB, and the practical measured value is −40dB. The 2-port multiple antenna system performance is assessed through the following metrics: Envelope Correlation Coefficient(ECC), Diversity Gain(DG), and Channel Capacity Loss(CCL). For the proposed 2-port multiple antenna the obtained values of ECC, DG and CLL are 0.004, 9.99dB and 0.4 bit/s/Hz. The results of the simulated structure are in good agreement with the fabricated structure. The result shows that defective ground is the better technique to achieve isolation between the closely placed antennas. The defective ground structure is the simplest technique in comparison with other techniques, such as metamaterial, energy band gap etc. The major novelty of the work includes, the design of a 2-port multiple antenna system with single slot and achieving the isolation more than −47dB without affecting the antenna resonating frequency.

Explicit Definitions for the Electromagnetic Energies in Electromagnetic Radiation and Mutual Coupling

It is still difficult to accurately evaluate the reactive electromagnetic energy and the radiative electromagnetic energy of a radiator, because there are no explicit expressions for them. This paper proposes to borrow the energy concept in the charged particle theory and separate the total electromagnetic energy of a radiator into three parts: a Coulomb–velocity energy, a radiative energy and a macroscopic Schott energy. Consequently, the Poynting vector is considered to include a real radiative power flow by the radiative energy and a pseudo power flow caused by the fluctuation of the reactive energy. The energies involved in the electromagnetic mutual coupling are separated in a similar way. All energies are defined with explicit expressions in which the vector potential plays an important role. The time domain formulation and the frequency domain formulation of the theory are consistent with each other. The theory is verified with the Hertzian dipole. Numerical examples demonstrate that this theory may provide proper interpretations for electromagnetic radiation and mutual coupling problems.

The Electric Field Evaluation for Vibrating Rain Droplets on the Overhead Line Conductors

The water droplets on the surface of the overhead line (OHL) conductors are subject to an intensive electric field, which induces electric force on the charged liquid surface. Under the combined action of the surface tension as well as the electric force, movement and deformation can be observed on those water droplets. These result in a re-distribution of charge density on the liquid surface and therefore a re-distribution of electric force. In this paper, in order to strengthen the understanding of this complex multi-physics problem of interaction and mutual coupling, the vibration characteristics of water droplets under alternating electric fields is studied using the finite element method (FEM). Parameters such as the volume size of the water droplet, static/dynamic contact angle between the water droplet and conductor surface and voltage level are studied in relation to the vibration characteristics. The reproducible correlation between the phase and amplitude of the water droplet vibration on the surface of the conductor and the applied voltage is established. According to the calculated instantaneous electric field strength, it is explained that protrusions such as water droplets are the starting point of corona discharge.

Downlink Spectral Efficiency of Massive MIMO Systems with Mutual Coupling

Massive multiple-input multiple-output (MIMO) is a profitable technique to greatly boost spectral efficiency, which has been embraced by the fifth-generation (5G) and sixth-generation (6G) mobile communication systems. By exploiting appropriate downlink precoding algorithms, base stations (BSs) equipped with a large number of antennas are able to provide service to multiple users as well as several cells at the same time and frequency. However, the mutual coupling effect due to the compact antenna array gives misleading results in massive MIMO communication systems. In this paper, we focus on the mutual coupling effect for massive MIMO systems with maximal ratio transmission (MRT), zero-forcing (ZF), regularize ZF (RZF), and minimum mean square error (MMSE) precoding to solve the mutual coupling problem. Additionally, we construct the closed-form expressions of the spectral efficiency (SE) to evaluate the effect of mutual coupling on system performance. Simulation results validate the effectiveness of the proposed mutual coupling effect assessment method and demonstrate the significant impacts of mutual coupling on massive MIMO system performance.

An Ultra‐Compact Spoof Surface Plasmon Polariton Transmission Line and Its Signal Integrity Analysis

An ultra‐compact spoof surface plasmon polariton (UCSSPP) transmission line (TL) based on a meander line is proposed, which can achieve almost the same transmission performance as the conventional rectangular‐groove SSPP TL, but the linewidth is greatly reduced by more than 40%. The coupling effect between two UCSSPP TLs in different line arrangements has been well studied, revealing that excellent crosstalk suppression can be achieved when two TLs are arranged back‐to‐back, while strong coupling occurs when they are arranged face‐to‐back or face‐to‐face. The signal integrity of back‐to‐back UCSSPP TLs is analyzed and demonstrated, which shows that the signal integrity can be greatly improved compared with microstrip (MS) TLs. In addition, based on the principle of mode mismatch, MS and UCSSPP TLs are arranged alternately to solve the mutual coupling problem in multi‐line systems. In contrast, benefiting from the strong coupling of face‐to‐face UCSSPP TLs, an ultra‐miniaturized SSPP coupler working at 9 GHz is designed, whose size can be reduced by over 75% compared with conventional MS coupler. The measurement results show good agreement with full‐wave simulations, indicating that the proposed UCSSPP TL has significant advantages in signal integrity and device miniaturization over previously reported SSPP TLs.

Position-enabled complex Toeplitz LISTA for DOA estimation with unknow mutual coupling

Unfolding iterative algorithms into deep networks can increase the rate of convergence which is amenable to Direction-of-arrival (DOA) estimation problems. However, there normally exists unknown mutual coupling between antenna array elements. In this paper, a novel Position-enAbled Complex Toeplitz Learned Iterative Shrinkage Thresholding Algorithm (PACT-LISTA) is proposed which makes use of the data driven method to solve the mutual coupling problem and improve the parameter estimation performance. First, a sparse recovery (SR) model is developed to explore the inherent Topelitz structure. In order to solve the SR problem, a Complex Toeplitz LISTA (CT-LISTA) network is proposed, which integrates the Toeplitz structure into the Complex LISTA (C-LISTA) network. By ignoring the amplitude and phase information of the recovered signal, the idea of position-priority is applied to further improve the estimation accuracy. Through an innovative iteration method, the system gradually converges to the optimized stable state, which is associated with an accuracy parameter. Simulations are provided to demonstrate that the proposed approach significantly outperforms the state of art methods.

Two-dimensional DOA estimation of the conformal array composed of the single electric dipole under blind polarization

To avoid the influence of blind polarization on parameter estimation, most conformal arrays arrange conformal antennas on single curvature geometry, or each antenna element of the conformal array is multiple channels composed of electric dipoles and magnetic loops. In practical applications, only a few conformal arrays have the single curvature characteristic, and the multiple channels of antenna element not only have the problem of mutual coupling, but also increase the computational burden. Therefore, a novel grid search method based on interpolation fitting idea is proposed to realize two-dimensional direction-of-arrival (2D DOA) estimation under blind polarization. Firstly, an interpolation fitting matrix (IFM) is designed according to the target four-dimensional region of interest (4D ROI), and then the search vector of grid search class method is pre-processed by the IFM to obtain a new search vector. In the end, the new search vector is used to measure 2D DOA. The proposed method has no requirements on the antenna structure, and each antenna element only needs a channel composed of the single electric dipole, so it has lower computational burden and smaller mutual coupling effect. Finally, the effectiveness of the proposed method is verified by the simulation results of the cylindrical array and parabolic array.

Multi-difference beams adaptive iterative monopulse estimation method for airborne radar

In the process of airborne radar parameters estimation, on the one hand, the adaptive sum and difference beam will be distorted near the main lobe clutter region; on the other hand, there is a coupling between the angle and Doppler frequency parameter estimation, which leads to the parameter estimation performance of the traditional sum and difference pulse estimation method severely degradation. In this paper, an adaptive iterative monopulse estimation method based on multi-difference beams is proposed. Firstly, two virtual difference beams are constructed based on the existing spatial and Doppler difference beams, secondly, the derivative constraint and zero constraint ensure that the formed difference beam is the optimal difference beam, thirdly, the generalized monopulse method is used to estimate parameters, and the mutual coupling problem of multi-parameter estimation is solved. Finally, the estimation accuracy of the target parameter is further improved by adaptive iteration. Simulation results verify the effectiveness of the proposed method.

Source Localization of EM Waves in the Near‐Field of Spherical Antenna Array in the Presence of Unknown Mutual Coupling

To obtain an antenna array with isotropic radiation, spherical antenna array (SAA) is the right array configuration. The challenges of locating signals transmitted within the proximity of antenna array have been investigated considerably in the literature. However, near‐field (NF) source localization of signals has hitherto not been investigated effectively using SAA in the presence of mutual coupling (MC). MC is another critical problem in antenna arrays. This paper presents an NF range and direction‐of‐arrival (DoA) estimation technique via the direction‐independent and signal invariant spherical harmonics (SH) characteristics in the presence of mutual coupling. The energy of electromagnetic (EM) signal on the surface of SAA is captured successfully using a proposed pressure interpolation approach. The DoA estimation within the NF region is then calculated via the distribution of pressure. The direction‐independent and signal invariant characteristics, which are SH features, are obtained using the DoA estimates in the NF region. We equally proposed a learning scheme that uses the source activity detection and convolutional neural network (CNN) to estimate the range of the NF source via the direction‐independent and signal invariant features. Considering the MC problem and using the DoA estimates, an accurate spectrum peak in the multipath situation in conjunction with MC and a sharper spectrum peak from a unique MC structure and smoothing algorithms are obtained. For ground truth performance evaluation of the SH features within the context of NF localization, a numerical experiment is conducted and measured data were used for analysis to incorporate the MC and consequently computed the root mean square error (RMSE) of the source range and NF DoA estimate. The results obtained from numerical experiments and measured data indicate the validity and effectiveness of the proposed approach. In addition, these results are motivating enough for the deployment of the proposed method in practical applications.

A modified feedforward hybrid active noise control system for vehicle

The feedforward hybrid active noise control (HANC) system combines the strengths of the narrowband ANC (NANC) system and the broadband ANC (BANC) system. Taking this advantage into account, this paper applies it to attenuate the vehicle interior noise mixed with narrowband and broadband components. However, in the HANC system, the NANC subsystem and BANC subsystem are fed a common error signal which depends on the combined secondary signals from the both subsystems. This causes the problem of mutual coupling and hence affects the noise reduction performance. To tackle the problem, we propose a modified HANC (MHANC) system in this paper. In the MHANC system, the error signal of each ANC subsystem is independently synthesized on the basis of the estimated primary and secondary signals. Note that the NANC system for engine order noise control suffers performance deterioration when the fluctuating real-time engine speed signal is used for constructing internal reference signals. For performance improvement, an enhanced NANC (ENANC) system is developed by smoothing the fluctuating engine speed signal. Meanwhile,the ENANC system is incorporated in the MHANC system to form an enhanced MHANC (EMHANC) system. Simulations were performed on the vehicle interior noise recorded under actual driving conditions. The corresponding results demonstrate the superiority of the proposed MHANC and EMHANC systems.

A novel algorithm for improving the differential protection of power transmission system

Current differential protection is simple in principle and is immune to power swings, load encroachment and mutual coupling problems. It provides simultaneous tripping at both ends of the transmission line and multi phase auto reclosing can be easily enabled because of its accuracy in determining the faulted phase and its communication channels. Conventional differential protection has certain issues to be dealt with before using it as a best alternative to distance protection for power transmission lines. Many researchers strive to improve the sensitivity of the current differential protection. Sensitivity and safety are opposing elements and increased sensitivity may sacrifice safety. In this paper, a new differential protection algorithm is proposed using the polarity of the terminal current DC transients. Different cases are studied in order to illustrate the applicability of the proposed differential approach. The proposed algorithm is able to detect high resistance faults and is not affected by line charging current, CT saturation. It improves the sensitivity without compromising the safety of the system. Simulations are carried out on 10 Bus system using PSCAD® software and obtained results are used for illustrating the efficiency of the proposed differential protection.

Mutual Coupling Reduction of 1×2 Microstrip Array Antenna Using MMAS-SSR

The issue that often arises and that is recently discussed in the development of antenna array is mutual coupling between elements. Elements of an antenna array are designed to be very close to one another in order to achieve a higher gain. However, such design could lead to an emerging problem of mutual coupling, resulting in a decreased efficiency and a change in beam pattern, mainly when using microstrip antenna. In order to reduce the mutual coupling effect, elements of the antenna are isolated using metamaterial absorber split square resonator structure (MMAS-SSR). In the experiments performed, two simple linear array microstrip antennas have been configured in a linear array, and a single line of metamaterial absorber structure was placed between them as an isolator. The observation has been conducted over experiments with and without the line of metamaterial absorber structure. The simulation and the measurement results obtained show that there is a mutual coupling reduction of 8 and 6 dB, respectively.

Decoupling self‐correcting method for non‐uniform dual circular array

According to the structural characteristics of non-uniform dual circular array (NDCA), a new method is proposed to solve the problem of mutual coupling error. In this algorithm, solving the mutual coupling problem of NDCA can be equivalent to solving that of non-uniform linear array (NLA). Firstly, the mutual coupling matrix is divided into several blocks. Then, each sub-block can be decomposed into the sum of several matrices with special characteristics by matrix addition method. As a result, the signal angles and mutual coupling coefficients can be conveniently decoupled. Compared with the iterative self-calibration algorithm, the proposed algorithm has a small amount of calculation. Moreover, it neither requires any prior information nor has problem of local convergence. The new method can accurately estimate the signal directions and mutual coupling coefficients.

Middle Subarray Interference Covariance Matrix Reconstruction Approach for Robust Adaptive Beamforming With Mutual Coupling

In this letter, a middle subarray interference-plus-noise covariance matrix (INCM) reconstruction approach is proposed to mitigate the mutual coupling problem in robust adaptive beamforming. In the proposed approach, the banded symmetric Toeplitz structure of mutual coupling matrix in the uniform linear array is employed. The INCM of middle subarray is first reconstructed by using the Capon spectrum of middle subarray to integrate over the possible interference region. Similarly, the desired signal covariance matrix of middle array is calculated over the desired signal region, and the desired signal steering vector of middle array is estimated. Finally, the proposed middle subarray beamformer weight vector is obtained. Simulation results validate the superiority and effectiveness of the proposed method.

Joint DOA and Polarization Estimation with Two Parallel Sparse Dipole Arrays

Electromagnetic vector sensors (EMVS) have attracted growing attention in recent years. However, the mutual coupling effects in practical EMVS arrays may seriously degrade the parameter estimation performance. In order to solve this problem, a novel array configuration consisting of two parallel sparse dipole arrays is proposed. Based on the spatially rotational invariance property between the two parallel arrays and the interdipole spacing inside each array, highly accurate but ambiguous direction-cosine estimates, coarse direction-of-arrival (DOA) estimates, and polarization parameter estimation can be obtained jointly. The coarse DOA estimates are then employed to disambiguate the phase ambiguities in the fine estimates. Compared with collocated EMVS, the proposed array overcomes the mutual coupling problem. Moreover, the DOA estimation accuracy is promoted due to the sparse array aperture extension. Simulation results demonstrate the effectiveness of the proposed algorithm.

Two-Dimensional Off-Grid DOA Estimation Using Unfolded Parallel Coprime Array

A two-dimensional (2-D) off-grid direction of arrival (DOA) estimation method using unfolded parallel coprime array (UPCA) is proposed. The proposed UPCA ensures large inter-element spacing, which is robust to the mutual coupling problem, and 2-D DOA estimation problem is transformed into one dimensional sparse representation (SR), which reduces the computation complexity. Besides, the off-grid DOA problem is taken into account and compensated through joint sparse recovery, which only requires a rough grid. Without the prior knowledge of source number, the proposed algorithm achieves improved DOA estimation results while requiring reduced computation complexity when compared to other SR-based methods. Simulation results verify the effectiveness of the algorithm.

A Reflection-Aware Unified Modeling and Linearization Approach for Power Amplifier Under Mismatch and Mutual Coupling

The behavior of a power amplifier (PA) is substantially affected by the output mismatch and mutual coupling in modern compact transmitters. To date, different works in the literature address the problem of coupling and mismatch separately, which are limited in terms of performance with a higher level of mismatch and mutual coupling. This paper identifies the reflection at the PA–antenna interface to be an effective parameter to unify the problem of mismatch and mutual coupling. Thus, a reflection-aware PA modeling and linearization method is proposed to compensate the adverse effect of mismatch and/or mutual coupling. The performance of the proposed method is investigated with a class AB and a Doherty PA under wide range of output mismatch and/or mutual coupling conditions with a 20-MHz WCDMA signal. The proposed method shows robust performance with an average adjacent channel power ratio better than 45 dBc. Such robust linearization performance under diverse output mismatch and mutual coupling conditions is highly desirable for modern and future communication systems that are subject to undergo rapid fluctuations under antenna matching and cross-coupling conditions.

Self-Calibration of Mutual Coupling for Non-uniform Cross-Array

Based on the non-uniform cross-array, a self-calibration algorithm is proposed to simultaneously estimate the angle of the impinging signal and the mutual coupling error. Firstly, the mutual coupling matrix of the non-uniform cross-array is divided into two parts: the mutual coupling matrix in non-uniform linear array and the mutual coupling matrix between non-uniform linear arrays. Then, the partitioned mutual coupling matrix is decomposed into the sum of several matrices with special characteristics. Thus, the decoupling of angle and mutual coupling coefficients is realized conveniently, so as to estimate the angle of the signal and mutual coupling coefficients. The proposed algorithm does not need auxiliary sources or prior information of the mutual coupling matrix. Moreover, it can reduce the search dimension, and hence, the amount of computation. Theoretical analysis and simulation results show that the proposed algorithm has improved angular resolution and it can estimate the mutual coupling error coefficients precisely. Hence, it can effectively solve the mutual coupling problem for the non-uniform cross-array.

Near-Field Interference Estimation Between Multilayer PCBs Using a Reciprocity-Based Filamentary-Element Coupling Model

In this paper, the near-field interference between two multilayer printed circuit boards (PCBs), which is resulted from the board-edge radiation and the board-edge coupling, is estimated by developing a reciprocity-based filamentary-element coupling (RBFEC) model. In the RBFEC model, the radiation of an $N$ -cavity multilayer PCB is modeled as the radiation from $N$ vertically parallel filamentary magnetic current sources. The near fields of a PCB are calculated based on the spatial Fourier transformation method. Then, by applying the reciprocity theorem to relate the radiated fields of the two PCBs that are on the same closed surface together, an analytical formula regarding the interference noise is obtained. The proposed model can be applied to handle the mutual-coupling problem between two multilayer PCBs that include vias and striplines. Because the coupling model is in the frequency domain, the dispersive behavior of the PCBs can be taken into account easily. The full-wave simulation based on the finite integration technique (FIT) and the experimental measurement are carried out to validate the proposed model. The results show that the proposed model has the same precision level as the FIT, but shows much higher computational efficiency than the FIT.