Effect Of Antenna Mutual Coupling Research Articles

The Effect of Antenna Mutual Coupling on MIMO Radar System Performance

Multiple-input multiple-output (MIMO) radar systems use orthogonal signaling to enable combined transmit and receive beamforming through signal processing on the received signals. Because of the combined role of transmit and receive arrays in this processing for monostatic MIMO radar, mutual coupling present in these arrays impacts the beamforming in a unique way. This paper presents a mathematical model of a MIMO radar with coupled antennas and appropriate radio frequency circuitry. Application of the model to evaluate radar detection of a single target demonstrates that coupling can result in target detection angles that are in error by as much as 12° and increase beamformer response sidelobe levels by as much as 8 dB. The results also show that a simple matching network can improve detection performance, particularly when array mutual coupling is high.

Cooperative Interference Control in Neighboring Passive Scattering Antennas

Passive backscattering links in scattering sensor arrays suffer from mutual coupling among closely spaced neighbor antennas. This effect results in an unmatched circuitry at input ports of antennas causing poor power harvesting, weak backscattering, overall low read rates. In this paper, a model for mutual coupling in a $N$ by $N$ scattering antenna arrays is discussed. We show by simulations and measurements that in a two scatterer system (one target and one neighbor antennas) the mutual coupling effect from the neighbor to the target varies depending on its load and also its location with respect to the target and the incident wave. We show that by load switching at neighbor antenna mutual coupling effect can be controlled to produce constructive interference at target antenna. Next, cooperative interference control by load switching is examined in a scattering antenna arrays. Simulation results show that by load switching at neighboring scatterers in a 3 by 3 scattering array the signal of a target antenna—which is proportional to its induced current—in the back row can be improved by ~21 dB.

On MIMO‐UFMC in the Presence of Phase Noise and Antenna Mutual Coupling

AbstractThe universal filtered multicarrier (UFMC) technique has been proposed as a waveform candidate for the fifth generation (5G) communications and beyond 5G. Compared with conventional orthogonal frequency division multiplexing (OFDM), UFMC has lower out‐of‐band emission and is also compatible with the multiple‐input multiple‐output (MIMO) technique. However, like other multicarrier waveforms, it suffers from phase noise of imperfect oscillator. In contrast to the rich literature on phase noise effect on MIMO‐OFDM (where the antenna mutual coupling effect is usually omitted though), there is little work investigating the phase noise effect on MIMO‐UFMC. In this paper, we study the MIMO‐UFMC systems in the presence of phase noise and with/without mutual coupling effect. A phase noise mitigation scheme for MIMO‐UFMC systems is presented. The scheme does not require detailed knowledge of the phase noise statistics and can effectively mitigate the phase noise within each UFMC symbol. Moreover, it is shown that at small antenna separations, the performance of the MIMO‐UFMC system taking the mutual coupling effect into account is better than that when the mutual coupling effect is overlooked.

Design of Maximally Sparse Antenna Arrays in the Presence of Mutual Coupling

An optimization framework is proposed that combines electromagnetic field simulations with an iterative ${\ell _1}$ -norm minimization procedure to synthesize optimally sparse antenna arrays. The proposed approach overcomes the limitation of design methodologies that assume idealized antenna elements employing equal (isolated or isotropic) element patterns, as these yield suboptimal solutions when the antenna mutual coupling effects cannot be ignored. The latter is demonstrated for arrays of relatively strongly coupled dipole radiators.

Adaptive Uncoupled Termination for Coupled Arrays in MIMO Systems

In this paper, we present an adaptive uncoupled matching network to compensate any performance degradation of compact multiple-input multiple-output (MIMO) systems due to antenna mutual coupling effects and channel variations. This method varies the antenna terminal loads per symbol-block, based on a random search algorithm, to find an optimum termination network that maximizes the performance metric, such as received power and capacity. It uses the received signals (voltages across the resistances of the terminal loads) to estimate or calculate the performance metric, in order to include the total effects in the optimization process. By applying the random search algorithm, our method does not require any knowledge of the array parameters such as impedance matrix, or derivatives of the performance metric(s) unlike other optimization techniques. We demonstrate this scheme by performing simulations to optimize the capacity of a 3 × 3 MIMO considering different propagation scenarios. We observe significant mean capacity improvements (more than 2 b/s/Hz) for all assumed propagation scenarios, when receive array antennas are spaced close as 0.05λ and terminated non-identically.

Successive User Scheduling Schemes for a Multiuser MIMO System Employing Generalized Channel Inversion

Generalized channel inversion (GCI) is a precoding technique for multiuser multiple-input multiple-output system. While producing each user's precoding matrix, GCI takes into account noise and thus it is more robust compared with alternative techniques such as block diagonalization technique in terms of sum rate capacity and frame error rate. In this paper, two suboptimal multiuser scheduling schemes for GCI are proposed that by scheduling a subset of mobile users nearly maximize the sum rate capacity. They employ an iterative approach involving a number of search steps. At each step, unselected mobile users are evaluated one by one, and only one of them is chosen according to given criteria. It is shown via computer simulations that the proposed schemes are capable of achieving a large portion of the sum rate capacity that is offered by an exhaustive search. The performance of the proposed multiuser scheduling schemes is evaluated when the antenna mutual coupling effects are taken into account at the mobile users' sides. Numerical results reveal that the presence of antenna mutual coupling can result in an increased sum rate capacity when the array inter-element spacing is in the range of 0.3---0.4 wavelength.

An External Calibration Method for Compensating for the Mutual Coupling Effect in Large Interferometric Aperture Synthesis Radiometers

This paper deals with the antenna mutual coupling effect in interferometric aperture synthesis radiometers (IASRs), which degrades the system radiometric performance. First, the conventional mutual impedance (CMI) is adopted to analyze the mutual coupling effect on the performance of IASR and a practical model of the coupled visibilities is developed. Based on the model, an external calibration method is then proposed to compensate for the mutual coupling effect. In this method, the measured visibilities are decoupled through the difference measurement between the original scene and a naturally occurring reference scene. Compared to the previous methods, the proposed method requires no extra additional hardware cost and has easier implementation and, therefore, fits for the large interferometric array radiometers. Experimental results validate the effectiveness of the proposed method.

Effect of Antenna Mutual Coupling on MIMO Channel Estimation and Capacity

This paper describes investigations into the antenna mutual coupling (MC) effect on channel estimation and capacity of a multiple-input multiple-output (MIMO) wireless communication system. The presented investigations close the gap existing in the previous works which assessed the effect of mutual coupling on MIMO capacity under the assumption of availability of perfect channel state information (CSI) at the receiver. The new approach assumes that the perfect CSI is not available due to channel estimation errors. The investigations are carried out for different spacing between array antenna elements producing a varying effect of mutual coupling on the channel estimation and the resulting MIMO channel capacity.

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.

Performance analysis of multiple-input multiple-output orthogonal frequency division multiplexing systems under the influence of antenna mutual coupling effect

The effect of antenna mutual coupling on signal correlation and bit error rate (BER) of a multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) system has been modelled. A MIMO-OFDM model with correlated channels is presented. The correlation matrices are determined with the antenna mutual coupling taken into account. The effect of antenna mutual coupling is characterised using the receiving and transmitting mutual impedances. A rigorous expression for the BER of the system employing quadrature phase-shift keying digital modulation is derived. A 2×2 MIMO-OFDM system using the Alamouti space–time block code for OFDM symbol transmission over 64 sub-channels spanning a 20 MHz band centred at 5.2 GHz is simulated. The simulated results show that the antenna mutual coupling has a significant effect on the BER performance, especially when the spacing between the antenna elements is small.

Investigations into Capacity of MIMO Ad Hoc Network Including Effects of Antenna Mutual Coupling

This paper reports on investigations into capacity of ad hoc network whose nodes are equipped with multiple element antennas (MEAs). The investigation of this multi-user Multiple Input Multiple Output (MIMO) system takes into account mutual coupling (MC) in addition to spatial correlation that is present in array antennas. A closed-form expression for an upper bound of mutual information (capacity) of MIMO ad hoc network is derived. An optimal signal transmission scheme is proposed to maximize the MIMO ad hoc network capacity. Simulation results for capacity of non-optimized and optimized cases of signal transmission are presented.

A New Spatial Correlation Formulation of Arbitrary AoA Scenarios

This letter presents a new approximate spatial correlation formulation of arbitrary angle-of-arrival (AoA) scenarios. The proposed approximation scheme can be applied to the parameterized three-dimensional (3-D) spatial correlation formulation taking antenna mutual coupling effect into consideration. Computation time can thus be significantly saved using the new spatial correlation formulation, which is beneficial for gauge of multiple-input multiple-output (MIMO) antenna systems.

Optimizing MIMO Channel Capacities Under the Influence of Antenna Mutual Coupling

This letter investigates the effect of antenna mutual coupling involving the unconventional concepts of transmitting and receiving mutual impedances on the multiple-input multiple-output (MIMO) channel capacity. Suitable expressions for the optimum power allocation strategy under the influence of antenna mutual coupling are derived. The undertaken numerical analysis shows a significant difference in the calculated results for the optimized average channel capacity for the cases when antenna mutual coupling is taken into account or neglected. The obtained results indicate that to obtain the correct optimum power allocation strategy antenna mutual coupling effects need to be properly taken into consideration. This claim is supported by computer simulation examples.

EFFECT OF MUTUAL COUPLING ON CAPACITY OF MIMO WIRELESS CHANNELS IN HIGH SNR SCENARIO

Theoretical results on the effect of antenna mutual coupling (MC) on capacity of multiple-input multiple-output (MIMO) wireless channels are presented in this paper with particular emphasis on the case of high signal to noise ratio (SNR) scenario. Two cases are considered, 1- channel capacity variations due to MC effect on correlation properties and target average receive SNR and 2- channel capacity variations due to MC effect on correlation properties at fixed average receive SNR. It is shown that the effect of MC on MIMO channel capacity can be positive or negative depending on the propagation environment spatial correlation properties and the characteristics of the transmitter and receiver MC matrices. Conditions where MC has positive and negative effects on MIMO channel capacity in the two considered cases are identified. Numerical results for half wavelength dipole antenna supporting the theoretical observations are presented.

Adaptive antennas and mimo systems for wireless communications: part II

he first part of this special issue contained eight articles that presented overviews, descriptions of different methods, performance analyses, and new ideas, all from a theoretical/simulation point of view. Part II includes articles that focus more on practical and experimental issues related to the presented topic. The first article of this issue discusses the advantages of reconfigurable antennas and the requirements for radio frequency microelectromechanical systems (RF MEMS). A simplified prototype of the reconfigurable antenna is also presented along with simulation and experimental results for impedance and radiation performance. The second article discusses a classification of multiantenna testbeds for training and research purposes. The authors present the characteristics, capabilities and cost of the testbeds, highlight their role in an educational environment and provide experimental results. The following article presents a multiple-input multipleoutput orthogonal frequency-division multiplexed (MIMOOFDM) prototype for next-generation wide area wireless networks. The uplink is based on an enhanced Universal Mobile Telecommunications System (UMTS) physical layer, the downlink on shared access MIMO-OFDM with adaptive modulation and coding. Measurements for different operational scenarios demonstrate the capabilities of the system. The fourth article describes the implementation issues related to the development of a 3 × 3 OFDM Bell Labs Layered Space-Time (BLAST) testbed for wireless metropolitan area networks. It then presents initial results for the performance and complexity of three BLAST detection techniques using experimental data from an indoor environment. The fifth article first surveys the principal space-time coding/decoding technologies for MIMO wireless LAN systems. Then it describes indoor channel sounding trials and employs the results to scope the expected performance of space-time codes in realistic deployments. The next article discusses the effects of antenna mutual coupling on correlation, radiation efficiency, diversity gain, and MIMO capacity. Measurements in a reverberation chamber and simulations are also provided to support the analysis. The last article of this issue presents a discussion of the classes of distortion that affect the performance of adaptive antennas. An eight-element circular array adaptive antenna testbed is employed to illustrate the impact of temperature on performance, while design techniques for calibration are also described. I would like to thank again all the authors who submitted their articles to this feature topic and also the many reviewers who took time out of their busy schedules and did an excellent job by providing detailed reviews.

DOA estimation of ultra-wideband EM waves with MUSIC and interferometry

We propose a direction-of-arrival (DOA) estimation technique for ultra-wideband electromagnetic waves, which allows for the effect of antenna mutual coupling. This technique is comprised of ultra-wideband interferometry, multiple signal classification (MUSIC), and databases. The effectiveness of our scheme is demonstrated through numerical examples.

A circuit model for mutual coupling analysis of a finite antenna array

Mutual coupling effects within an antenna array play a very important role in the areas of EMC (electromagnetic compatibility) and antenna array design. A circuit model is developed to represent the input admittance of an antenna array with a finite number of elements. This model consists of a component to represent the input admittance of an isolated antenna element and infinite shunt components with each to represent different degrees of antenna mutual coupling effects. Twersky's (1952) algorithm of multiple scattering analysis is used to illustrate the physical meaning of each circuit component. Numerical results show that good accuracy for the antenna input admittance calculation can be obtained by using this model to the second order approximation. As the array is large and sparse, a very small amount of computation can yield good accuracy. This model is shown not only to be numerically efficient compared to the full wave analysis using the moment method, but also to give a physical insight into the antenna array mutual coupling mechanism. Furthermore, this model has no limitation on antenna array geometry and excitation.