Mutual Coupling Compensation Research Articles

Effects of Ground Constituent Parameters on Array Mutual Coupling for DOA Estimation

Effects of ground constituent parameters on the mutual coupling (MC) of monopole antenna array are investigated. This work augments an existing MC compensation technique for ground-based antennas and proposes reduction in mutual coupling for antennas over finite ground as compared to the perfect ground. The work is investigated by finite element method analysis, and numerical results are presented. A factor of 4 decrease in both the real and imaginary parts of the mutual coupling is observed when considering a poor ground versus a perfectly conducting one, for quarter-wave monopoles in receiving mode. A simulated result to show the errors in direction-of-arrival (DOA) estimation with actual realization of the environment is also presented.

Self-Tuning Synthesis Filter against Mutual Coupling and Interferences for GNSS and Its Implementation on Embedded Board

Traditional spatial-temporal adaptive signal processing techniques are often applied to conduct narrowband and wideband interferences. However, its mitigation performance degrades greatly due to mutual coupling. To solve this problem, this paper aims to utilize a spatial-temporal self-tuning synthesis filter capable of mutual coupling compensation and interference mitigation. The spatial filter and temporal filter are to compensate for the effect of mutual coupling and interference mitigation, respectively. Self-tuning mechanism is to adopt least square (LS) and minimum variable distortionless response- (MVDR-) based method to adjust spatial and temporal weights of antenna array. The experiment platform is established by the embedded development board. Simulation and experiment results demonstrate that the proposed method can effectively compensate for mutual coupling, mitigate the cochannel interference up to 30 dB, and enhance the acquisition performance of receivers in global navigation satellite system (GNSS).

Mutual Coupling Compensation for Direction-of-Arrival Estimations Using the Receiving-Mutual-Impedance Method

A short review of the receiving-mutual-impedance method (RMIM) for mutual coupling compensation in direction finding applications using linear array is conducted. The differences between the conventional-mutual-impedance method (CMIM) and RMIM, as well as the three different determination methods for receiving mutual impedance (RMI), will be discussed in details. As an example, direction finding with better accuracies is used for demonstrating the superiority of mutual coupling compensation using RMIM.

Effective Mutual Coupling Compensation for Direction-of-Arrival Estimations using a New, Accurate Determination Method for the Receiving Mutual Impedance

Performance degradation due to the mutual coupling effect of antenna arrays in direction-of-arrival (DOA) estimations has been well known, and many mutual coupling compensation methods have been proposed throughout the years. In particular, the mutual coupling effect becomes significant when the antenna elements are closely spaced, which is difficult to compensate. In this paper, a new, accurate method is introduced to determine the receiving mutual impedances of antenna arrays with closely spaced omni-directional antenna elements. This new method uses a number of plane wave sources coming from different directions to determine the receiving mutual impedances of a particular antenna element with all other antenna elements in the array in a single step. This step is repeated for all the antenna elements in the array, and the full mutual impedance matrix of the array is thus obtained. Using the Matrix Pencil Method (MPM), DOA estimations using eight-element arrays were used to demonstrate the validity and accuracy of this new method.

Mutual coupling compensation based on direct data domain algorithms

In this paper, we present an adaptive algorithm based on direct data domain which can compensate the mutual coupling with only one snapshot of the received signals. Without any auxiliary sensors and calibration sources, this algorithm can accurately estimate the coupling coefficients and recover the desired signal. Numerical simulation shows that the recovery of the desired signal is accurate in the presence of mutual coupling.

Improved mutual coupling compensation in compact antenna arrays

A new method for the characterisation of receiving mutual impedances of compact arrays with omni-directional antenna elements is proposed. Based on a large number of incident waves coming from different directions, the new method is able to calculate the receiving mutual impedances of omni-directional antennas based on a system of equations that characterise the received terminal voltages at different incident wave directions. In the new method, the receiving mutual impedances of all the antenna elements are calculated together in a single equation with the scattering effect from all antenna elements in the array being taken into account. Compared to the previous methods for the characterisation of the receiving mutual impedances, the new method preserves the boundary conditions of the original electromagnetic problem and produces much more accurate results on receiving mutual impedances, especially for compact antenna arrays. Direction finding examples based on the new method demonstrate its superior performance over existing methods.

A Note on the Mutual-Coupling Problems in Transmitting and Receiving Antenna Arrays

In antenna arrays, mutual coupling between antenna elements is well known as an undesired effect, which degrades the performance of array signal-processing algorithms. The compensation of such an undesired effect has been a popular research topic throughout the years. Various approaches for mutual-coupling compensation have been developed, and they can easily be found in the open literature. In general, the mutual-coupling problems for a transmitting and receiving array are different, even if the physical geometry of the array remains unchanged. However, it seems that antenna engineers are not well aware of such differences in the analysis of receiving antenna arrays. In this note, the mutual-coupling problems in transmitting and receiving antenna arrays are revisited. The differences between the mutual coupling and mutual impedances for transmitting and receiving antenna arrays are explained. It is concluded that the mutual-coupling problems of transmitting and receiving arrays are in general different, and hence different mutual impedances should be used for mutual-coupling analysis and compensation.

Mutual-Coupling Compensation in Time-Modulated Antenna Arrays for Flat-Top Pattern Synthesis

A method that can be used to compensate for the mutual-coupling effect in time-modulated antenna arrays for synthesizing flat-top patterns is proposed in this article. Based on the measured complex embedded element patterns, the differential evolution algorithm is employed to optimize time sequences and phase excitation of each element in the array and to suppress the sideband level, leaving the amplitude excitations to be uniform. A −20-dB sidelobe level flat-top pattern is successfully synthesized in which the ripple level of the mainlobe is lower than 0.5 dB and the sideband level is lower than −10 dB. An S-band eight-element printed dipole with a double-layered structure linear array is used in the experiment to verify the proposed method, and the measured results are in good agreement with the simulated results.

Frequency-Independent Approximate Compensation of Mutual Coupling in a Linear Array Antenna

The method of the frequency-independent compensation of the strongest mutual coupling (between the neighbor elements only) in a linear array antenna is suggested and studied. It is shown that in the suggested method both the scheme and the parameters of a decoupling multiport network do not depend on properties of the array elements as well as on frequency. An example of a seven-element array is considered.

THE MULTIPLE ANTENNA INDUCED EMF METHOD FOR THE PRECISE CALCULATION OF THE COUPLING MATRIX IN A RECEIVING ANTENNA ARRAY

Practical antenna array designs generally require that the elements are separated by electrically short distances. The resultant mutual coupling often adversely afiects the achievable performance. Various methods are available to quantify the efiects of mutual coupling in arrays and improve performance through mutual coupling compensation. Mutual coupling is often described by a coupling matrix that relates the coupled and uncoupled quantities. Unfortunately, the accuracy with which the coupling matrix can be calculated is highly dependent on both the method selected and the frequency. This is a signiflcant limitation for wideband analysis where the coupling matrix needs to be calculated accurately at all frequencies of interest. This paper introduces a novel method for the precise calculation of the coupling matrix at any frequency of interest. It is an extension of the induced EMF method to multiple array elements. The method has the important practical advantage of being independent of the numerical technique used in the analysis. Since the coupling matrix is calculated by exciting the elements in the transmission mode, the method resembles well-known network analysis. However, as outlined in the paper, there are subtle difierences between the two approaches, which lead to more accurate results with the new proposed method. It is also demonstrated that antennas with arbitrary geometries and illuminations are handled accurately by the method.

Mutual Coupling Compensation in Arrays Using a Spherical Wave Expansion of the Radiated Field

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This letter presents a flexible method to compensate the interelement mutual coupling (MC) effects that may degrade the field pattern of an array of real and coupled antennas. A closed-expression for a mutual coupling compensation matrix (MCCM) is derived. The MCCM is used to compensate the presence of the real individual elements' patterns and the interelement MC effects for any excitations obtained with an isotropic-based pattern synthesis method. The MCCM is calculated from the generalized scattering matrix (GSM) of an antenna array and the spherical mode expansion (SME) of its radiated field. For a given array, this MCCM has to be calculated only once since it only depends on the radiating and scattering characteristics of the antenna elements as well as on their location in the array. Conditions regarding null field pattern directions can also be reinforced in the MCCM. To compute the GSM of the array and the SME of the radiated field, a validated full-wave hybrid and modular methodology is used. Numerical results of synthesized patterns where the MC effects have been compensated are presented for arrays made up of dielectric resonator antennas. </para>

New mutual coupling compensation method and its application in DOA estimation

A new mutual coupling compensation method based on a new mutual impedance matrix, as well as its application to dipole arrays, are proposed. This new mutual impedance matrix is deduced by electromotive force (EMF) method, based on the current distribution obtained by the characteristic basis function method. It appears in a concise and explicit formulation that facilitates the numerical calculation. The compensation performance is demonstrated and evaluated through its application in direction of arrival (DOA) estimation. Numerical results show that the proposed method exhibits excellent compensation performance compared with conventional mutual impedance matrix approaches.

Compensation for the mutual coupling effect in uniform circular arrays for 2D DOA estimations employing the maximum likelihood technique

An effective compensation method for the mutual coupling effect in uniform circular arrays (UCAs) employed for two-dimensional (2D) direction-of-arrival (DOA) estimations is introduced. A new 2D DOA searching algorithm using the maximum likelihood technique optimized by the emperor selective genetic algorithm (ML-EMSGA) is introduced for use with UCAs. This method circumvents the difficulty of dealing with coherent signals in 2D DOA estimations. ML-EMSGA is less computationally demanding than the maximum likelihood method (MLM) and statistically more efficient. Our study shows that ML-EMSGA can be effectively combined with the proposed compensation method, which is based on the introduction of a new mutual impedance, to give very accurate and robust 2D DOA estimation results. The structure of mutual impedance matrix for UCAs under the compensation method is fully explained. The theory of the ML-EMSGA for the UCAs is formulated. Computer simulation examples on several synthetic scenarios are presented to demonstrate the effectiveness of the mutual coupling compensation method and the superior performance of the ML-EMSGA for UCAs.

The MMSE Algorithm and Mutual Coupling for Adaptive Arrays

In this paper, the minimum-mean-square-error (MMSE) in a mutual coupling (MC) environment is derived. The MMSE is slightly degraded by MC with receiver noise but it is not affected with environmental noise. Analysis also shows that data domain MC compensation cannot improve the minimum MSE even if the estimate of MC is accurate. The simulations also show that MC slows down the convergence of the least mean square algorithm.

On the improvement of the mutual coupling compensation in DOA estimation

A new and exact calculation method for the mutual impedance matrix of receiving arrays is proposed. The mutual impedance matrix is derived from electromagnetic boundary conditions and can be used to relate the coupling free open-circuit voltages, instead of the conventional ones, to the measured voltages. A remarkable improvement on compensation for the coupling effects is shown in the direction finding applications, while a simple relationship between measured terminal voltages and the coupling free voltages is remained.

A Simple Mutual Coupling Compensation Technique in Array of Single-Mode Elements by a Weighted Mutual Coupling Matrix Based on the Impedance Matrix

High-resolution Direction-of-Arrival (DOA) estimation techniques for antenna arrays have been widely desired in many applications such as smart antennas, RF position location, and RFID system. To realize high-resolution capability of the techniques, precise array calibration is necessary. For an array of single-mode elements, a calibration matrix derived by the open-circuit method is the simplest one. Unfortunately, calibration performance of the method is not enough for the high-reslution DOA estimation techniques. In this paper, we consider problems of the calibration matrix derived by the method, and show that errors in the matrix can be effectively removed by an optimal diagonal weight coefficient. In the proposed compensation technique, the number of newly introduced parameters, or unknowns, is only one for an array of the identical elements. Performance of the simple compensation technique is verified numerically and experimentally.

A Novel Online Mutual Coupling Compensation Algorithm for Uniform and Linear Arrays

In this paper, a novel online mutual coupling compensation algorithm especially tailored to uniform and linear arrays is presented. It is conceived to simultaneously compensate for mutual coupling and estimate the direction-of-arrivals (DOAs) of signals impinging on the array since the estimated calibration matrix can be embedded within any classical super-resolution direction-finding method. An alternating minimization procedure based on closed-form solutions is performed to estimate the mutual coupling matrix in the field of complex symmetric Toeplitz matrices. Unlike many existing array calibration methods, it requires neither the presence of calibration sources nor previous calibration information as initialization. Computer simulations show the effectiveness of the proposed technique and prove that the nice statistical properties of classical super-resolution DOA estimation algorithms can be restored despite the presence of mutual coupling

Mutual Coupling Compensation in UCAs: Simulations and Experiment

In a beamforming system, mutual coupling among the elements can significantly degrade the system performance. However, the mutual coupling effects can be compensated if an accurate model of mutual coupling is available. This paper utilizes a mutual coupling matrix model to compensate mutual coupling in the beamforming of a uniform circular array. In addition, a circular array of dipoles was built and measurements were performed. The predictions are compared with measurements, and verified with results from full-wave simulations

Mutual coupling compensation in time modulated linear antenna arrays

A practical approach to compensate for the mutual coupling effect in low sidelobe time modulated linear antenna arrays is proposed. Taking into account the measured complex embedded element patterns, the compensated element weights and time sequences are optimized by the differential evolution (DE) algorithm. The proposed approach is experimentally verified by the successful realization of a -30 dB sidelobe level discrete Taylor pattern from a 16-element time modulated linear array. Numerical results are compared with measured data and good agreement is reported.

Comparison of mutual coupling compensation to dummy columns in adaptive antenna systems

Compensation for mutual coupling in antenna arrays by matrix multiplication is compared to the use of dummy elements. A least squares estimation of the coupling matrix is made, including co- and cross-polar coupling. We show that compensation for measurements off the phase center is important as well as a proper assumption of the ideal element pattern. We study the performance of a dual polarized patch array with respect to far-field phase error, signal-to-interference reduction, and cross-polarization level. In all aspects, the performance of the compensation method exceeds or equals the use of dummy elements.