Multi-input Multi-output Array Research Articles

Mutual Coupling Compensation for Compact MIMO Radar

A calibration method to compensate for the mutual coupling and channel imbalance in a compact multi-input multi-output (MIMO) radar array based on turn table measurements is proposed. Two mutual coupling matrices, one for the transmit array and the other for the receive array, are used to model the relationship between the ideal manifold and the measured manifold. The practical factors such as the nonisotropic element pattern and the displacement of the array phase center are also taken into account. All the unknowns are determined by solving the nonlinear least-squares fitting problem iteratively. Using two coupling matrices consists of the mutual coupling mechanism in an MIMO array and has better calibration performance than using one matrix for the virtual array. It also reduces the dimension of the matrix and hence the computation load of calibration. Measurements by a microstrip array with two transmitters and four receivers are used to verify its effectiveness in angle estimation, beamforming, and superresolution of close targets.

Deca‐band structure reutilization MIMO antenna for 4G / 5G full‐screen metal frame smartphone operation

This article presents a deca-band multi-input multi-output (MIMO) antenna for full-screen metal frame smartphone, which covers wideband of GSM850, GSM900, DCS, PCS, UMTS, LTE2300, LTE2500, WLAN/WiMAX, N78, and sub-6 GHz (4.8–5.1 GHz) bands table. Two kinds of antenna structures are positioned on the long side edge and form two 2 × 2 MIMO array, covering the low-band (824–960 MHz) and mid-band (1710–2690 MHz/3300–3800 MHz), respectively. Four slot antennas are distributed on both sides of the short side edge. Each slot is connected to an antenna structure on the long side edge, sharing one port to form the high-band structure. By reutilization the low and mid-band structures, the high-band structure can achieved a wide band bandwidth without any additional matching structures. The high-band structure is composed of 4 × 4 MIMO array and covers the band of 4800–5825 MHz. A prototype of the proposed MIMO antenna is fabricated and measured. The isolation of the antenna is larger than 15 dB, the efficiencies are between 31% and 63%, and the ECCs is less than 0.3, which shows that the proposed antenna has great potential in the future 4G/5G smartphone application.

Design and Performance Investigation of Miniaturized Multi‐Wideband Patch Antenna for Multiple Terahertz Applications

In this paper, a highly efficient multiband optimized slotted pentagonal terahertz patch antenna and its 2 × 2 multi-input multi-output (MIMO) planar array is proposed for multiple terahertz (THz) applications like high-speed indoor communications, explosive detections, arms detection, medical imaging, pharmaceutical analysis, and industrial inspections, etc. Here, the proposed patch antenna is developed from the simple rectangular patch antenna (SRPA) by optimizing the shape of radiating patch and ground plane. Such proposed antenna is designed on the transparent polyimide substrate material having a dielectric constant of ℇr = 3.5 and thickness 21.5 µm. The particle swarm optimization (PSO) technique is used to enhance the performance parameters of proposed antenna. The performance parameters like reflection coefficient, gain, directivity, radiation pattern, and antenna efficiency are computed at the resonating frequencies of proposed antenna. It covers wide bandwidth, which resonates at 3.00 THz, 4.85 THz, 7.02 THz, 8.87 THz, 9.43 THz, and 10.785 THz frequencies having reflection coefficient less than −10 dB. It is also noted that as compared to early reported THz antennas, it has achieved a maximum gain of 13.92 dB and radiation efficiency of 85.77% within the resonating band. Also, a 2 × 2 MIMO antenna array is designed using an optimized antenna element for more effective terahertz communication. The performance of such MIMO array is computed in terms of the transmission coefficient, envelope correlation coefficient (ECC), and Mean effective gain. It has achieved <−15 dB isolation between the antenna elements. The proposed antenna could be a successful choice for multiple terahertz applications.

Demonstration of 3-D Security Imaging at 24 GHz With a 1-D Sparse MIMO Array

A 3-D security imaging experiment at 24 GHz is demonstrated with a 1-D sparse multi-input multi-output (MIMO) array. The MIMO array is an 8 transmission/16 reception arc array to achieve real-aperture imaging along the vertical dimension. It is time-switching multiplexed with a low-cost frequency modulated continuous wave transceiver working at 22-26 GHz. A calibration procedure is proposed to calibrate the channel imbalance across the MIMO array. The experiment is conducted on humans moving on a cart, where we take advantage of the linear motion of humans to form inverse synthetic aperture along the horizontal dimension. To track the motion of humans, a 3-D depth camera is used as an auxiliary sensor to capture the rough position of the target to aid synthetic aperture radar imaging. The back-projection imaging algorithm is implemented on a graphics processing unit for quasi-real-time operations. Finally, experiments are conducted with a real human with concealed objects and a preliminary automatic object detection algorithm based on convolutional neural networks is developed and evaluated on real data.

Self-Curing Decoupling Technique for MIMO Antenna Arrays in Mobile Terminals

The self-curing decoupling technique is substantially extended to apply to multi-input multi-output (MIMO) antenna arrays in mobile terminals. Using this proposed technique, the mutual coupling between antennas can be reduced by inlaying lumped element capacitors on the ground plane. The decoupling method does not require any physical connection or obstruction between coupled antennas. The significance of the proposed decoupling technique is fourfold: 1) it works for inverted-F antennas (IFAs), monopole antennas, and loop antennas, the most three commonly used antenna forms for mobile terminals; 2) the inherent improvement on matching conditions after decoupling; 3) the flexibility in implementation owing to its detachment from the antenna body; and 4) the applicability to an array with more than two elements. Four demonstrating examples, including two IFAs, two monopole antennas, two loop antennas, and a MIMO array with four elements of different antenna types are studied by EM modeling, passive tests, and MIMO over-the-air (OTA) measurements. The experimental results show that significant improvements in port isolation (from 9 to 30 dB), total efficiency (from 53% to 69%), and above all, the system data throughput can be achieved. The working mechanism of the method is revealed and justified through the partial element equivalent circuit (PEEC) model in the fifth example.

A Wide Stopband Filtering Patch Antenna and its Application in MIMO System

This communication presents a wide stopband filtering antenna element and its application in multi-input multi-output (MIMO) system. Microstrip terminated coupled lines and a rectangle patch are utilized to generate the filtering function. By varying the length of the parallel coupled lines and open-circuited stubs, multiple transmission zeros can be introduced in the spurious band. Appropriate positioning the location of these transmission zeros enables a wide harmonic suppression. To demonstrate the proposed method, a wide stopband filtering antenna is designed and further applied in a four-element MIMO array. The measured and simulated results agree well. The proposed MIMO antenna obtains an attenuation of 12.6 dB up to $6.6\times $ the center frequency.

Effective joint DOA-DOD estimation for the coexistence of uncorrelated and coherent signals in massive multi-input multi-output array systems

This paper deals with the joint direction-of-arrival (DOA) and direction-of-departure (DOD) estimation when the uncorrelated and coherent (i.e., fully correlated) narrowband signals coexist in multiple-input multiple-output (MIMO) array systems. Two new approaches based on weighted subspace fitting and oblique projection for two-dimensional direction estimation, i.e., WSFOPDE and improved WSFOPDE, are proposed. In the WSFOPDE approach, the basic procedure includes three stages. First, the DOA of all signals can be directly acquired by minimizing a reduced-dimensional weighted subspace fitting function. Then, the DOA information of uncorrelated signals are discerned by a classifying indicator; and subsequently, their auto-paired transmit steering vectors with respect to DOD information are derived. Finally, via a new Toeplitz-structured oblique projection, an virtual MIMO array data with only coherent signals remaining is constructed to assist the corresponding auto-paired DOD estimation. In order to promote the accuracy of angle estimation, we also design an improved version. It inherits the above basic procedure and, meanwhile, introduces one-dimensional local DOA spectrum searching to refine the DOA-DOD estimation. Compared with some existing strategies, WSFOPDE and its improved version perform better from the united perspective of computational complexity and estimation accuracy. Numerical simulations verify the advantages and also demonstrate that both can be served as a better alternative to the competitors.

Power, Linearity, and Efficiency Prediction for MIMO Arrays With Antenna Coupling

Modern and future transmitter architectures are being driven toward multi-input multi-output (MIMO) transceivers, which make use of several radio frequency (RF) power amplifiers (PAs) to drive an antenna array. When moving to high integration scenarios, as is expected for fifth-generation communications, the isolation between the array and the PAs is often removed. Since the array elements are electromagnetically coupled, the waves fed to the antennas are also driving the output ports of the PAs. This effect creates an apparent variable load at the output of each PA, depending on the operation of the transmitter. In this system, the behavior of each PA cannot be fully described solely as a function of its input, as it will change according to the coupled signal. To predict and understand the behavior of these MIMO systems, simulation becomes a powerful tool. These simulators should be able to reproduce the main figures of merit (FoMs) of the transmitter, namely, output power, distortion, and efficiency. In this paper, we show how a recently proposed dc behavior model and an RF signal behavior model can be used in simulation setups to predict the MIMO transmitter FoMs of interest.

A New Iterative Approach in SINR Improvement of MIMO Radars by Using Combination of Orthogonal Waveforms

In this paper we consider joint waveform and filter design in multi-input multi-output (MIMO) radars in the presence of signal dependent interference to improve signal-to-interference-plus-noise ratio (SINR) of received signals. We have proposed two new iterative methods for this in which instead of direct design of waveforms, the coefficients of orthogonal waveform combinations are designed. In the first method, coefficients of combinations are calculated by solving a convex optimization problem. By extending the first method, we have proposed a method for multi-target case in presence of signal dependent interference. However, the computational complexity of the first method is high and therefore we have proposed the second method, which is more suitable for real time applications. In the second method, in each step, waveform combination coefficients and received filter coefficients are designed in closed form. Simulation results show that the proposed methods can achieve higher SINR in comparison to other methods which are used in MIMO and phased array radars.

DOD and DOA estimation in bistatic MIMO radar for nested and coprime array with closed-form DOF

ABSTRACTIt is well known that sparse array can offer better angle resolution than that of uniform linear array (ULA) in the same number of physical sensors. But in bistatic minimum redundancy sparse array multi-input multi-output (MIMO) radar, it cannot offer closed-form degree of freedom (DOF) for the arbitrary number of sensors with direction of departure and direction of arrival estimation. Therefore, this article introduces a nested array and coprime array into sparse array to solve the problem. First, construct no holes difference-coarray by extracting specified covariance matrix elements. Then, transform the difference-coarray into ULA within bistatic MIMO radar through some mathematical operations. As a result, many angle estimation methods for traditional ULA can be applied to the sparse bistatic MIMO array radar. The proposed algorithm offers closed-form DOFs for sparse array and the array aperture is much larger than that of ULA with identical number of sensors. The usefulness of the proposed methods is verified through computer simulations.

Design of reconfigurable coplanar waveguide‐fed planar antenna for multiband multi‐input–multi‐output applications

A new design of frequency reconfigurable planar coplanar waveguide-fed array antenna for multiband MIMO (multi-input–multi-output) applications is presented in this study. The proposed two elements MIMO array antenna consists of two identical basic reconfigurable antenna elements. Each basic antenna structure consists of two quarter-wavelength resonators and is capable of operating in WLAN (wireless area network) and WiMAX frequency bands. The centre frequencies of the operating bands are controllable independently by tuning the length of the corresponding resonators. Employing switches on the proposed structure has led to three different switchable operations [WiMAX (3.36–3.7 GHz), WLAN (5–5.8 GHz) and WiMAX and WLAN (3.17–3.77 and 5.13–5.88 GHz) simultaneously]. Moreover, by arranging the antenna elements in an orthogonal alignment in space and using polarisation diversity technique, the multipath performance of the presented MIMO antenna is improved. The fabricated reconfigurable MIMO antenna has a compact size of 48.5 × 25 mm2 while having more than 16 dB isolation level between its ports for all its various switchable performances. The measured results reveal that the proposed antenna can be a good candidate for modern multiband MIMO applications.

A Cluster-Based Dual-Adaptive Topology Control Approach in Wireless Sensor Networks.

Multi-Input Multi-Output (MIMO) can improve wireless network performance. Sensors are usually single-antenna devices due to the high hardware complexity and cost, so several sensors are used to form virtual MIMO array, which is a desirable approach to efficiently take advantage of MIMO gains. Also, in large Wireless Sensor Networks (WSNs), clustering can improve the network scalability, which is an effective topology control approach. The existing virtual MIMO-based clustering schemes do not either fully explore the benefits of MIMO or adaptively determine the clustering ranges. Also, clustering mechanism needs to be further improved to enhance the cluster structure life. In this paper, we propose an improved clustering scheme for virtual MIMO-based topology construction (ICV-MIMO), which can determine adaptively not only the inter-cluster transmission modes but also the clustering ranges. Through the rational division of cluster head function and the optimization of cluster head selection criteria and information exchange process, the ICV-MIMO scheme effectively reduces the network energy consumption and improves the lifetime of the cluster structure when compared with the existing typical virtual MIMO-based scheme. Moreover, the message overhead and time complexity are still in the same order of magnitude.

DOD and DOA Estimation in Bistatic Non-Uniform Multiple-Input Multiple-Output Radar Systems

This letter investigates the joint estimation of the direction of departure (DOD) and direction of arrival (DOA) for multi-input multi-output (MIMO) radar systems. A novel estimation method based on non-uniform array configuration is proposed and the practical identifiability of the corresponding parameter is analyzed. The key idea is to use the Doppler diversity to construct a virtual MIMO array. Through the theoretical proof, we demonstrate that the proposed method can provide much stronger parameter identifiability than the conventional ones, and also can improve the parameter estimation performance. Numerical simulations verify the effectiveness of the proposed algorithm.

A triple‐band WLAN/WiMAX printed monopole antenna for MIMO applications

AbstractA triple‐band multi‐input multi‐output (MIMO) antenna is presented.The proposed antenna consists of a C‐shaped monopole antenna that provides dual‐band resonant antenna. By protruding an L‐shaped parasitic strip on the ground plane, a third band as well as enhancement of the isolation between two ports in MIMO array is achieved. The proposed antenna can cover 2.1–2.6, 3.3–4, and 5.4–6 GHz, which are allocated for WLAN and WiMAX applications. The proposed triple‐band antenna structure is used in different two‐element MIMO arrays. Simulation results show that the S11, S12, and S22 of the MIMO arrays are independent of the position of the two‐element. The results show good S‐parameters, high peak gain and radiation efficiency, and stable radiation patterns among the triple‐band coverage. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:1321–1325, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26799

Improved Joint DOD and DOA Estimation for MIMO Array With Velocity Receive Sensors

This letter discusses the problem of direction of departure (DOD) and direction of arrival (DOA) estimation for multi-input multi-output (MIMO) array system, which is configured with multiple transmit sensors and multiple velocity receive sensors. Reference presented a successive multiple signal classification MUSIC algorithm for joint estimation of DOD and DOA for the bistatic MIMO array system with velocity receive sensors. In this letter, we propose an improved joint DOD and DOA estimation algorithm, which has much better angle estimation performance and lower complexity than the successive MUSIC algorithm in . Furthermore, the proposed algorithm can be suitable for irregular array geometry, obtain automatically paired 2-D angle estimation, and avoid 2-D searching. Simulation results verify the usefulness of the proposed algorithm.

Antenna Array Optimization Using Dipole Models for MIMO Applications

A very fast and efficient method for designing compact antenna arrays preserving the maximum channel capacity of multi input multi output (MIMO) systems using infinitesimal dipole model (IDM) theory is presented. Using this method each antenna element is replaced by a set of infinitesimal dipoles producing the same electric fields of the antenna. The recently introduced Invasive weed optimization (IWO) algorithm is employed to find the infinitesimal dipole models. The algorithm is applied to a planar inverted F-antenna designed as an element of a compact array for MIMO applications. Using the obtained IDMs, self and mutual admittances between the antennas are predicted. Therefore, correlation coefficients of the MIMO array system are achieved using S-parameters. Having the correlation of the system, the location and orientation of each antenna are optimized to find the minimum correlation value for the MIMO antenna system. Using the optimization technique, very low cross correlation coefficient is obtained for very close antennas over a finite ground plane.

Joint DOD and DOA Estimation for MIMO Array With Velocity Receive Sensors

This letter investigates the problem of joint estimation of the direction of departure (DOD) and the direction of arrival (DOA) for multi-input multi-output (MIMO) array systems. A new bistatic MIMO array system, configured with multiple transmit sensors and multiple velocity receive sensors is introduced, and a new joint DOD and DOA estimation algorithm is proposed. The key idea behind the proposed algorithm is to use the DOA information embedded in the velocity sensors to start 1-D MUSIC searches for the DOD and DOA in succession. The proposed successive MUSIC algorithm is suitable for irregular array geometry, imposes less constraint on the receive sensor spacing, and requires no parameter pairing nor two-dimensional searching.