Influence Of Mutual Coupling Research Articles

A Novel Generalized Nested Array MIMO Radar for DOA Estimation with Increased Degrees of Freedom and Low Mutual Coupling.

In array signal processing, the mutual coupling among physical sensors can inevitably affect the estimation of the direction of arrival (DOA). Despite the fact that multiple-input and multiple-output (MIMO) radar can provide greater degrees of freedom (DOFs), the influence of mutual coupling is largely overlooked in many current MIMO radar designs. To tackle this issue, we propose the utilization of a generalized nested array (GNA) in transmitter array and we introduce an expansion factor into the nested array in the receiver array. Thereby, a novel GNA-MIMO radar is put forward. The proposed MIMO radar offers O(N4) consecutive DOFs with N sensors and avoids the adverse effects of high mutual coupling caused by closely located sensors. Furthermore, we derive the closed-form expressions for the position of physical sensors and the attainable consecutive DOFs of the proposed MIMO radar. Through simulation experiments, we demonstrate the superior accuracy of the proposed MIMO configuration in DOA estimation and angle resolution under the condition of mutual coupling effect.

A Two-Step Marginal-Restraint Mandrel-Free Spinning Method for Accuracy in Forming Large, Special-Shaped Aluminum Alloy Tank Domes

The special-shaped tank dome of a launch vehicle is a large, thin-walled, curved structure that is difficult to form using the conventional center-restraint spinning method. This study proposes a two-step marginal-restraint mandrel-free spinning method for forming large domes. The finite element analysis results indicate that a larger roller fillet radius and larger feed ratios lead to a larger upper convex angle and the minimum thickness value for the bottom contour. This study explored the impact of shape parameter variations on the upper convexity and transition rounding angle on forming accuracy. The results show that the convexity of the bottom of the special-shaped domes increases with a larger roller fillet radius and larger feed ratios while the overall height decreases. The forming accuracy is adversely affected by larger transition rounding angles and smaller upper convexities. For the accurate forming of domes, the mutual coupling influence during two-step forming should be considered, and a suitable process and suitable trajectory compensation parameters must be carefully selected. Finally, the study verified that a two-step marginal-restraint mandrel-free spinning method with a 10 mm roller fillet radius, a 2 mm/r feed ratio, and the corresponding trajectory compensation can achieve the precise forming of 2250 mm thin-walled special-shaped domes.

A Mutiparameter Joint Estimation Algorithm for Dual-Polarized Cylindrical Conformal Array in the Presence of Mutual Coupling

In this article, we proposed a multiparameter joint estimation algorithm based on the dual-polarized cylindrical conformal array (DCCA) in the presence of mutual coupling. Using the characteristic of the dual-polarized cylindrical conformal array, 2D direction-of-arrival (DOA) estimation can be divided into 1D estimations of elevation and azimuth. Sensors on the boundary of the DCCA are set as auxiliary sensors to eliminate the influence of mutual coupling. Then, elevation can be estimated by the generalized eigenvalues utilizing signal subspace eigenvectors (GEESE). After that, polarization sensitivity can be eliminated by projection transformation and the proposed dual-polarized forward-backward smoothing algorithm. Consequently, a dual-polarized spatial spectrum can be developed to estimate the azimuth based on the estimated elevation. Furthermore, the angles of the signals can be reestimated to improve the accuracy of DOA estimation. Simulation results confirm the effectiveness of the proposed algorithm.

A Novel Rollover Warning Approach for Commercial Vehicles Using Unscented Kalman Filter

Roll responses of the semitrailer and the tractor provide higher lead time and characterise the roll instability of the commercial vehicles subjected to directional manoeuvres at highway speeds. This paper proposes a novel rollover index based on the synthesized roll angles of the tractor and trailer. Owing to the poor measurability, the unscented Kalman filter (UKF) algorithm is used to estimate the roll angle of the track and trailer, respectively. Meanwhile, different weight coefficients are considered in the rollover index to eliminate the influence of mutual coupling between the tractor and the trailer and improve the accuracy of the warning. For the practical implementation of the algorithm, a two-stage rollover warning method triggered by the video and audio is finally proposed to reduce the possibilities of false warnings. Co-simulation is presented to prove the validity of the proposed rollover warning approach.

Robust angle estimation algorithm for MIMO radar based on tensor analysis and reduced-dimension subspace reconstruction

A robust angle estimation algorithm based on tensor analysis and reduced-dimension subspace reconstruction is proposed for the noncircular signals with unknown mutual coupling in MIMO radar. The proposed algorithm constructs a special tensor analysis to capture the non-circular characteristics and multi-dimensional structure of non-circular signals, and can eliminate the influence of mutual coupling in the tensor domain. The signal subspace is obtained by using high-order singular value decomposition (HOSVD), and the direction-of-departure (DOD) of the target is obtained by combining the real value subspace estimation of direction of arrival (DOA). In addition, according to the working principle and echo model of bistatic MIMO radar, combined with array signal processing, the angle estimation algorithm of reduced-dimension subspace reconstruction is proposed, which can effectively solve the angle estimation problem of bistatic MIMO radar, reduce the calculation cost, improve the robustness of the algorithm, and solve the problem that angle matching cannot be realized after dimension reduction. The simulation results show that the algorithm proposed in this paper has good performance in recognition.

Antenna Performance Improvement in Elliptical Array Using RMI Method of Mutual Coupling Compensation

The number of wireless electronic gadgets used in mobile communication, vehicle collision avoidance system, compact radars, etc. is extremely increasing at a rapid rate. Thus, the characteristics of the antennas involved in these gadgets are to be designed very stringently so as to avoid interferences & coupling and to improve compatibility, susceptibility, etc. Compact smart antenna with improved performance is highly essential to meet this challenging scenario. Mutual coupling between various elements of an array is one of the main factors which can be considered for improvement of performance of the antenna. Influence of mutual coupling on performance of the antenna is considered in this paper and various techniques to minimize this effect are presented. Effect of mutual coupling on radiation characteristics of the antenna can be compensated employing various methods like Conventional Mutual Impedance (CMI), Receiving Mutual Impedance (RMI). Analysis is presented as comparison between the two methods for different number of elements in the array. Analysis is also presented for different geometries of the array like circular and elliptical for improved performance. The results show performance improvement in the proposed array for parameters like SNR and Speed of convergence.

Direction-of-Arrival Estimation: Measurement using compact antenna arrays under the influence of mutual coupling

This article investigates the accuracy of direction-of-arrival (DOA) estimations using compact antenna arrays under the influence of mutual coupling. We model the entire electromagnetic problem using the moment method such that the undesirable mutual coupling effect is taken into account accurately. We decouple the received signals using the receiving-mutual-impedance method (RMIM) and perform the DOA estimation using the matrix pencil method (MPM) through a Monte Carlo simulation approach. Although the signals are strongly distorted by mutual coupling, we show that increasing the number of elements within a small array aperture can significantly improve the estimation accuracy. The findings show that the RMIM can effectively compensate for mutual coupling for arrays with an aperture of a factor of a wavelength. Such findings are crucial to the development of compact arrays in various applications.

Influence of Mutual Coupling and Current Distribution Errors on Advanced Phased Antenna Array Nulling Synthesis

Phased antenna array synthesis procedures based on the amplitude-phase and only-phase distributions providing the side lobe cancellation in a required direction are presented. A receiving antenna array was considered. It is characterized by the direction of the main beam for receiving the useful signal and the additional nulling direction. The required amplitude—phase distribution along the array is provided by the phase shifters and controllable attenuators/amplifiers. Moreover the modified synthesis procedure that takes into account the mutual coupling influence in the antenna array was proposed. Finally the radiation pattern transformation under the influence of the current distribution errors connected with a quality of phase shifters and attenuators/amplifiers was investigated.

Optimization of Training Signal Transmission for Estimating MIMO Channel under Antenna Mutual Coupling Conditions

This paper reports investigations on the effect of antenna mutual coupling on performance of training-based Multiple-Input Multiple-Output (MIMO) channel estimation. The influence of mutual coupling is assessed for two training-based channel estimation methods, Scaled Least Square (SLS) and Minimum Mean Square Error (MMSE). It is shown that the accuracy of MIMO channel estimation is governed by the sum of eigenvalues of channel correlation matrix which in turn is influenced by the mutual coupling in transmitting and receiving array antennas. A water-filling-based procedure is proposed to optimize the training signal transmission to minimize the MIMO channel estimation errors.

Impact of Mutual Coupling on Adaptive Switching Between MIMO Transmission Strategies and Antenna Configurations

Adaptive switching between multiple-input multiple-output (MIMO) transmission strategies like diversity and spatial multiplexing is a flexible approach to respond to channel variations. It is desirable to obtain accurate estimates of the switching points between these transmission schemes to realize the capacity gains made possible by adaptive switching. In this paper, it is shown that the accuracy of switching point estimates for switching between statistical beamforming and spatial multiplexing is improved by taking into account the effects of mutual coupling between antenna array elements. The impact of mutual coupling on the ergodic capacities of these two transmission strategies is analyzed, by deriving expressions for the same. Adaptive switching between combinations of transmission strategies and antenna array configurations (using reconfigurable antenna arrays) is shown to produce maximum capacity gains. Expressions for the switching points between transmission strategies and/or antenna configurations, including mutual coupling effects, are derived and used to explore the influence of mutual coupling on the estimates. Finally, measurements taken from reconfigurable rectangular patch antenna arrays are used to validate the analytical results.

Impact of Antenna Coupling on 2 $\times$ 2 MIMO Communications

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> The impact of mutual coupling induced by two closely spaced minimum scattering antennas at the subscriber unit on 2 <formula formulatype="inline"><tex>$\times$</tex></formula> 2 multiple-input multiple-output channels and communications is investigated. Both (de)correlation effects and variations of antenna gain resulting from coupling mechanisms are considered. Relationships between coupling and correlations/channel Frobenius norm are discussed, pointing out the role of the interelement spacing, the array orientation, and the richness of scattering. The analysis also yields useful insight into the influence of mutual coupling on capacity and system performance. </para>

Influence of Mutual Coupling due to Zero-Sequence On The Performance of Distance Relay

Influence of Mutual Coupling due to Zero-Sequence On The Performance of Distance Relay

Design considerations for low antenna correlation and mutual coupling reduction in multi antenna terminals

AbstractThe influence of mutual coupling on the envelope correlation between two identical planar inverted F‐antennas (PIFA) are investigated. The capacity of a multiple‐input multiple‐output (MIMO) antenna system strongly depends on the correlation between the antennas. By placing two antennas in a fixed area, it is found that the envelope correlation could be halved simply by proper mutual orientation. The set‐ups that maximise the distances between the open ends of the PIFAs yield the lowest mutual coupling as well as the lowest envelope correlations. It is found that the envelope correlation is 0.8 when the PIFAs are oriented in parallel. The envelope correlation can be decreased to 0.4 by rotating one of the PIFAs by 180 degrees. Copyright © 2006 AEIT

On the electromagnetic scattering of a chaff cloud

Scattering characteristics of a chaff are investigated, using a cloud of wire dipoles. The influence of mutual coupling between the dipoles is taken into account. The cloud is studied in terms of the resonant conditions. Algorithms to specify the stochastic distribution of the dipole positions and orientations are constructed. Finally, the possibility of tracing an obscure target behind the cloud is examined.

Temporal Reference Algorithms versus Spatial Reference Algorithms forSmart Antennas

This paper compares algorithms from three different classes of adaptation schemes for smart antennas – the switched beam approach, a Temporal-Reference (TR) technique based on Direct Matrix Inversion or Least Squares adaptation, and a Spatial-Reference (SR) technique with direction finding by Unitary ESPRIT. The simulations are based on a channel model including directions of arrival (DOA) and flat Rayleigh fading. The fading signal is spread out in angle over several degrees dependent on the distance of the mobile from the base station. The results indicate that, in the uplink, TR algorithms and SR algorithms perform equally well, given perfect synchronization and successful user identification (for SR algorithms). TR algorithms are the most robust against close-by interference. For a Uniform Linear Array (ULA) with M=8 elements and an element spacing ofd equal to half a wavelength, they are able to separate two co-channel users that are as close as 5 degrees in angle. For an angular threshold as low as 10° an 8-element ULA is also sufficient to obtain nearly the same BER performance as for a single user. As concerns SR algorithms, we demonstrate their applicability to situations where no discrete DOAs exist, as it is the case in mobile communications. Mutual coupling of individual antenna elements increases the BER by an order of magnitude for the switched beam approach and for SR algorithms, in contrast to TR algorithms, where the influence of mutual coupling on the BER is negligible.

DETERMINING THE FREQUENCY CHARACTERISTICS OF POWER NETWORKS USING ATP

The interaction between the natural oscillatory characteristic of a nonlinear system with a periodic driving source gives rise to oscillations whose frequency depends on the amplitude of the oscillation. The existence of combination tones (both harmonic and subharmonic) in such systems, gives rise to complicated oscillatory behaviour induced by either the occurrence of the saturation of transformer cores or by system conditions leading to the reduction in the magnitude of damping. By studying the frequency characteristics (Bode plot) of single phase nonlinear power networks, the possible oscillatory modes that may be excited can be anticipated. This aspect is then extended to three phase power networks to include the influence of mutual coupling between phases and unbalance due to non-transposition of transmission lines. The Frequency Scan feature in the Alternative Transients Program (ATP) is used for that purpose.

Influence of mutual coupling between parallel circuits on the setting of distance protection

The significant mutual-coupling impedances between the two circuits in double-circuit overhead-line construction are considered. The impedances measured by distance-protection relays are examined, both for stability for faults outside the protected zone and for operation for faults within the protected zone. This is done for different primary-system-circuit arrangements and for the condition where one circuit is out of service and earthed at both terminals. Some proposals for a practical setting policy are made.