Multiple-input Multiple-output Array Research Articles

Reduced-complexity multiple parameters estimation via toeplitz matrix triple iteration reconstruction with bistatic MIMO radar

In this advanced exploration, we focus on multiple parameters estimation in bistatic Multiple-Input Multiple-Output (MIMO) radar systems, a crucial technique for target localization and imaging. Our research innovatively addresses the joint estimation of the Direction of Departure (DOD), Direction of Arrival (DOA), and Doppler frequency for incoherent targets. We propose a novel approach that significantly reduces computational complexity by utilizing the Temporal-Spatial Nested Sampling Model (TSNSM). Our methodology begins with a multi-linear mapping mechanism to efficiently eliminate unnecessary virtual Degrees of Freedom (DOFs) and reorganize the remaining ones. We then employ the Toeplitz matrix triple iteration reconstruction method, surpassing the traditional Temporal-Spatial Smoothing Window (TSSW) approach, to mitigate the single snapshot effect and reduce computational demands. We further refine the high-dimensional ESPRIT algorithm for joint estimation of DOD, DOA, and Doppler frequency, eliminating the need for additional parameter pairing. Moreover, we meticulously derive the Cramér-Rao Bound (CRB) for the TSNSM. This signal model allows for a second expansion of DOFs in time and space domains, achieving high precision in target angle and Doppler frequency estimation with low computational complexity. Our adaptable algorithm is validated through simulations and is suitable for sparse array MIMO radars with various structures, ensuring higher precision in parameter estimation with less complexity burden.

Tri-arm MIMO array antenna pair for mobile phone applications

Abstract An 8 × 8 tri-arm multiple-input multiple-output (MIMO) array using novel even–odd mode decouplers is presented. To decouple the directly connected driven ports on the tri-arm antenna pair, a T-shaped stub working as an even-mode decoupler and a narrow strip working as an odd-mode decoupler are elaborately introduced. Therefore, the even-mode and odd-mode impedances cross with the antenna input impedance, and a deep coupling zero is achieved at this cross frequency. Finally, the proposed 8 × 8 MIMO array was developed, fabricated, and measured for further performance verification. The measured results show that the proposed array can have a wide isolation bandwidth of 17.2 % with a compact size of 0.44λ 0 × 0.08λ 0 and zero clearance requirement on the ground plane. The diversity performances are also investigated with the measured worst envelope correlation coefficient less than 0.05.

Joint design of transmit precoding and antenna selection for multi-user multi-target MIMO DFRC

Dual-function radar and communications (DFRC) systems based on multiple-input multiple-output (MIMO) arrays have received considerable attention in recent years due to their excellent ability to alleviate spectrum congestion. The MIMO DFRC systems enable high-resolution detection of multiple targets while communicating with multiple users simultaneously. However, MIMO arrays require numerous radio frequency (RF) units and suffer a strong mutual coupling among antennas, resulting in significant system overhead and performance degradation, respectively. In light of this, this paper investigates the joint optimization of transmit precoding and antenna selection for MIMO DFRC systems, aiming to improve the angular ambiguity function with a guaranteed communication quality of service (QoS) using a small number of antennas. To address the resultant non-convex optimization problem, both the indirect and direct precoding methods are proposed. In the former, the waveform covariance and antenna selection vector are first jointly optimized via a promoted sparsity along the covariance diagonal, followed by the precoding matrix indirectly derived from the optimal covariance. In the latter, the precoding matrix is directly optimized via an imposed group sparsity under the communication QoS and power constraints. Simulation results demonstrate that the proposed sparse MIMO DFRC system with fewer active antennas can achieve comparable dual-functional performance to that of the full array system.

Systematic methods for the synthesis of equidistant MIMO arrays

Abstract. Finding a feasible antenna arrangement for multiple input multiple output (MIMO) arrays to serve a specific purpose is a first crucial step towards a successful MIMO radar system design. Design methods to synthesize uniformly weighted and equidistant MIMO arrays are proposed and investigated. The methods can be used to gain a design foundation for 1D or 2D arrays without software tools or programming effort. Since the presented approach does not consider electromagnetic fields, electromagnetic full-wave simulations might be required additionally. The method is based on sequentially copying and displacing antenna groups with the help of a number scheme. A nomenclature is proposed to classify the degrees of freedom in the design procedure. If the antennas are aligned to a uniform grid, a polynomial representation of the array can be chosen alternatively. This method is beneficial when redundancies of a produced array and where they appear must be analyzed. A new design problem arises when an array is to consist of only transceiving antennas, which can be analyzed with polynomial multiplication. One strategy to find a suitable MIMO array consisting of transceiver elements is given and evaluated.

Machine learning with A MIMO Antenna for Wireless Communication Systems

Multiple-input multiple-output (MIMO) antenna is a technology that uses multiple antennas at both the transmitter and receiver to improve the performance of wireless communication systems. One of the challenges in designing MIMO antennas is to reduce the complexity of the antenna array, while still maintaining good performance. One way to reduce complexity is to use shared antennas. Shared antennas are antennas that are used by multiple elements of the MIMO array. This can reduce the number of required antennas and simplify the design of the antenna array. The B-shape of the MIMO antenna by using CST program can also be used to reduce complexity. For example, hexagonal MIMO antennas have been shown to have good performance and can be implemented with a simple design. Additionally, the use of defected ground planes (DGPs) can be used to improve the isolation between the elements of a MIMO antenna array, which can also reduce complexity. The design of MIMO antennas is a complex and challenging task. However, by using shared antennas and other design techniques and AI, it is possible to reduce the complexity of MIMO antennas while still maintaining good performance.

A dual operating (27/38 GHz) high performance 2 × 4 MIMO antenna array for 5G new radio applications

This article presents an unique configuration of Multiple-Input Multiple-Output (MIMO) antenna array for functioning at 27/38 GHz millimeter-wave 5G new radio (NR) frequency bands applications. The suggested antenna is constructed with four MIMO elements, containing total of eight identical patches arranged in a 2 × 4 array configuration. The array also includes a separate non-connected rectangular ground plane with an overall dimension of 32.4 × 32.8 × 0.8 mm3. The single radiating patch elements are designed using spline resonator with H-shaped structures. The prototype model is realized using low cost FR-4 substrate and the obtained measurement results validate the analyzed simulated results. The suggested MIMO array antenna offers dual band operation with an impedance bandwidth of 8400 MHz covering 22 to 30.4 GHz and 8500 MHz ranging from 36.1 to 44.6 GHz. The proposed antenna achieves a peak gain of 8.75 dBi when operating at 27 GHz and 18.59 dBi at 38.1 GHz. Furthermore, it shows circular polarization characteristics by offering the axial ratio values significantly lower than 3 dB at 27 GHz and 38.1 GHz frequency bands. Additionally, the results indicate the favourable values of the diversity performance parameters with reference to Mean effective gain (MEG), Envelope correlation coefficient (ECC), Diversity gain (DG), Total active reflection coefficient (TARC), and Channel capacity loss (CCL). Moreover, it demonstrates high isolation (<−20 dB) within the desired bandwidth. These superior characteristics make it compatible for 5G NR frequency bands N257(26.5-29.5 GHz), N258 (24.5-27.5 GHz), N259 (39.5-43.5 GHz) and N260 (37-40 GHz), enabling its use in various countries including the China, European Union, Sweden, Korea, Japan, United States of America, Canada and Australia.

Miniaturized High Gain Broadband 16‐Element MIMO Array Using Planar Artificial Magnetic Conductor With Enhanced Isolation for WLAN/WiMAX Applications

AbstractA low‐profile 16‐element printed dipole antenna (PDA) array backed by a planar artificial magnetic conductor (AMC) is introduced for multiple‐input multiple‐output (MIMO) wireless communications. The proposed 16‐element MIMO array loaded by a 13 × 13 AMC reflector with various polarized directions exhibits a low‐profile wideband structure, which includes the broad measured bandwidths from 4.25 to 7.25 GHz with increased gains (&gt;8 dBi) and high efficiency. The high isolation between the 16 elements with diverse polarizations is larger than 27 dB and reaches 67 dB over the operating band for MIMO systems. The suggested PDA with a microstrip V‐shaped dipole excited by a V‐shaped microstrip feedline is used to expand the broad simulated band spanning 5.34–6.70 GHz (S11 ≤ −10 dB). Moreover, the suggested 13 × 13 planar fractal AMC reflector is loaded into the PDA array to exhibit a reflection coefficient, S11, of less than −10 dB across the band of 4.26–6.90 GHz for wireless local area network and worldwide interoperability for microwave access applications. The proposed design with AMC compared to the design without AMC exhibits a size reduction of 50.3%, increased gain up to 8.2 dBi, and excellent impedance matching with unidirectional radiation patterns. The novel AMC unit cell is realized based on the planar patch with inserted slots to operate at 6.10 GHz with an AMC band spanning 5.15–7.10 GHz (32%).

Wideband self-isolated MIMO antenna element based on multiple adjacent modes coupling current cancellation for 5G mobile terminal application

Abstract In this article, a wideband self-isolated multiple-input multiple-output (MIMO) antenna element based on multiple adjacent modes coupling current cancellation is proposed for 5G mobile terminal. The wideband self-isolated technology based on multiple adjacent mode coupling current cancellation are demonstrated. With the combination of five adjacent loop modes, the −6 dB bandwidth of the proposed self-isolated element can cover 3.3–3.8 GHz and 4.4–5.0 GHz. Finally, an 8 × 8 MIMO array is constructed by arranging eight proposed wideband self-isolated antenna elements on the two long sides of the mobile terminal. Simulated and measured results show that the isolation of 8 × 8 MIMO array exceeds 15 dB without any decoupling structures in the operating frequency band. The proposed antenna elements are simply arranged to obtain a wideband high isolation MIMO array, and it is a good choice for 5G mobile terminal.

Millimeter-Wave Imaging via Circular-Arc MIMO Arrays

Millimeter-wave (MMW) imaging has a promising prospect in application of concealed weapons detection. To that end, we propose a circular-arc multiple-input–multiple-output (MIMO) array scheme with uniformly spaced transmit and receive antennas along the horizontal-arc direction while scanning along the vertical direction. The antenna beams of the circular-arc MIMO array can provide more uniform coverage of the imaging scene than those of linear or planar MIMO arrays, which is especially important for the detection of concealed weapons carried by personnel. Furthermore, a near-field 3-D imaging technique, based on spatial frequency-domain processing, is presented together with a detailed analysis of sampling criteria and resolutions. Numerical and experimental results are provided to demonstrate the performance of the proposed method in comparison with those of the currently most used array schemes and imaging algorithms.

A Broadband MIMO Antenna Based on Multimodes for 5G Smartphone Applications

In this letter, an eight-element broadband multiple-input multiple-output (MIMO) antenna array with a simple structure based on multiple modes is presented, which covers 3.3–6 GHz for fifth-generation (5G) smartphone. Double coupled-fed loop modes and a slot mode are well excited by the feeding strip connecting with the tuning branch. The broadband antenna is well designed without loading any lumped elements, thanks to the tuning branch on the side frames. Furthermore, the polarization diversity technique is exploited to improve isolation. As a result, the MIMO system operates in the 3.3-6 GHz (S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> < -6 dB) with desirable isolation higher than 12.1 dB, which satisfies the coverage of the 5G communication bands: n77/n78/n79 and 5G WLAN. Besides, acceptable efficiency and envelope correlation coefficients (ECCs) of lower than 0.2 can also be obtained, which demonstrates that the presented MIMO array has potential for the mobile communication of 5G smartphones.

A Compact Wideband (22–44GHz) Printed 2×4 MIMO Array Antenna with High Gain for 26/28/38GHz Millimeter-Wave 5G Applications

In this work, a novel multiple input multiple output (MIMO) array antenna system with a large bandwidth and high gain has been simulated, analyzed, fabricated, and measured. The proposed antenna is structured in [Formula: see text] patch configuration along with a cross shaped ground plane loaded with four square and one circular shaped defect. The projected antenna occupies a total size of [Formula: see text]. Several slots in an elliptic form have been added to the patches to achieve the required results in terms of wide bandwidth and high gain. The MIMO antenna array is fabricated and experimentally tested to confirm the simulation results. The suggested MIMO array antenna offers an impedance bandwidth of 22[Formula: see text]GHz covering 22–44[Formula: see text]GHz wide range of frequencies with a high peak gain of 17[Formula: see text]dBi at 38[Formula: see text]GHz. The designed MIMO antenna offers superior diversity performance and it supports several 5G NR bands n257/n258/n259/n260/n261 in the mm-wave spectrum. The suggested MIMO antenna supports 5G application bands that are deployed in UK, USA, China, Europe, Canada, India, and Europe.

Low‐profile wideband four‐element MIMO array using Giuseppe Peano AMC surface with improved efficiency and isolation for WLAN systems

AbstractA low profile four‐element multiple‐input multiple‐output (MIMO) array of printed dipole antenna (PDA) backed by second iteration of Giuseppe Peano fractal artificial magnetic conductor (AMC) is introduced for broadband wireless communications. First, a suggested PDA with a pair of microstrip E‐shaped dipoles excited by an E‐shaped microstrip feedline is used to expand the bandwidth in the range of 5.47–6.92 GHz (S11 ≤ −10 dB). Then, the suggested 4 × 4 Giuseppe Peano fractal AMC reflector is loaded into the PDA to exhibit −10 dB measured impedance bandwidth from 4.21 to 7.06 GHz (50.61%) for wireless local area network (WLAN) and worldwide interoperability for microwave access (WiMAX) applications. The proposed four‐element MIMO array loaded by 6 × 6 AMC reflector with diverse polarizations of elements introduces a low profile wideband structure. The measured results of four elements include the broad bandwidths from 4.3 to 7.05 GHz with enhanced gains (more than 8 dBi) and high efficiencies. The high isolations between the four elements with diverse polarizations are obtained larger than 26.5 dB and they reach 66 dB over the operating bandwidth for MIMO systems. The suggested PDA with AMC compared to the PDA without AMC exhibits a size reduction of 51.33%, enhanced radiation efficiency up to 94%, and excellent impedance matching with uni‐directional radiation patterns.

A Compact Wideband Antenna With Suppressed Mutual Coupling for 5G MIMO Applications

A novel miniaturized wideband dual-polarized antenna, based on cross magnetic dipoles and a backed cavity, is proposed in this letter for multiple-input–multiple-output (MIMO) applications. The dipoles with exponential curvature edges deliver inherent wideband character to the radiator. Four parasitic resonators are introduced to miniaturize the top radiator's conducting area and lower the Q-factor of the whole structure, enhancing the antenna's impedance matching. Different from conventional direct-fed cross-dipole antennas, a wideband hybrid ring coupler is applied to excite the two dipoles simultaneously in-phase/out-of-phase to generate the ±45° polarization. The dimension of the proposed antenna is 42.5 mm × 42.5 mm × 18 mm, which is only 0.48 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">λ_L</i> × 0.48 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">λ_L</i> × 0.2 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">λ_L</i> at the frequency of 3.4 GHz. The corresponding MIMO array is studied, showing a low mutual coupling and envelope correlation coefficient level across the band, and an outperforming front-back-ratio performance. The antenna is prototyped and measured. The measurement results agree with those of the simulations well .

Experimental investigation of scatterer‐array‐based decorrelation technique applied to real multiple‐input multiple‐output base station

AbstractIn this paper, a scatterer‐array‐based decorrelation method for improving the multiple‐input multiple‐output (MIMO) performance is proposed for a real application of base station (BS) operating at 780 MHz with a 20‐MHz communication bandwidth. The antenna correlation is reduced by loading a scatterer array designed to increase the MIMO array's effective inter‐element spacing. As a result, the diversity measure is improved, which in turn benefits the MIMO capacity. This method is demonstrated first in simulation to check its performance, which shows about 4% and 20% improvements in MIMO capacity over 20‐MHz communication bandwidth in single‐cell and multi‐cell scenarios, respectively. Then it is applied to a real BS in a realistic urban micro scenario for experimental verification, showing a noticeable throughput improvement without degrading the power coverage of the BS. Note that this is the first time that the scatterer‐array‐based decorrelation technique has been applied to increase the MIMO throughput of a real BS in a real‐life scenario, which thoroughly demonstrates the promising application potential of this technique.

Massive MIMO Array Design With High Isolation by Using Decoupling Cavity

This brief proposes an isolation enhancement method for massive multiple-input multiple-output arrays using decoupling cavities (DC). The proposed DC is made of a pure Polypropylene (PP) board, and an air cavity is engraved on it. The DC has high transmission in the normal direction and a high insertion loss in the tangential direction of the arrays, respectively. The DC operates with a broadband response due to the low dielectric constant of the substrate. An example of a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4\mathbf {\times }4$ </tex-math></inline-formula> array with an inter-element distance around half wavelength is designed to verify the proposed isolation enhancement method. The triple-layers stacked DC are employed seamlessly above the array. The isolation of the array was enhanced to 24 dB within the bandwidth of 4.21-4.79 GHz. At the same time, the radiation characteristics of the arrays before and after loading the DC basically keep consistent.

Joint DOA, range and polarization estimation based on geometric algebra for near-field non-circular source with a symmetric MIMO array

Multiple-input multiple-output (MIMO) radar is a new type of radar with excellent performance in target detection and parameter estimations. The MIMO radar equipped with electromagnetic vector sensors (EMVSs) can record multi-dimensional information of the electromagnetic (EM) signal. Traditional methods based on long vector model cannot preserve orthogonality between the outputs of each component of the EMVS and have high computational complexity. In this paper, a novel geometric algebra (GA)-based localization method is proposed for direction of arrival (DOA), range, and polarization estimation of near-field (NF) non-circular (NC) sources for a symmetric MIMO array. First, the proposed method converts the output of an EMVS into a multi-vector through a GA matrix transformation. Then, the DOA and range parameters can be estimated by searching the one-dimensional (1-D) spectrum based on the GA-based NC rank reduction (GANC-RARE) algorithm. Finally, the polarization can be estimated by employing estimated DOAs and ranges based on the modified GA-based NC multiple signal classification (MGANC-MUSIC) algorithm. The computational complexity analysis demonstrates that our solution improves memory spaces of the covariance matrix and reduces computation efforts of the eigenvalue decomposition (EVD). The simulation results show the superiority and reliability of our proposed method in model error and coherent noise environment.

A Grating-Lobes Suppression Method for Wideband MIMO Millimeter-Wave Imaging Arrays

This article proposes a novel method for eliminating the first grating-lobe of wideband multiple-input multiple-output (MIMO) millimeter-wave imaging array. It exploits the position shift phenomenon of the first grating-lobe and can achieve grating-lobes suppression without additional calculation. The far-field formula for the first grating-lobe is derived, and the cause of its shift phenomenon in both azimuth and range directions is analyzed. The proposed multiapodization (MA) method can be used to cut off the part of the shifted grating-lobes while maintaining the resolution. However, nonsparse targets still have the far-field residual grating-lobes after MA. To solve the problem, the position formula and the detailed derivation of the residual grating-lobes are given. Therefore, a pixel search (PS) method can be used to remove them. The proposed MA can also be utilized to suppress the residual grating-lobes of the near-field MIMO array. Both simulated and experimental data in different system regimes and frequencies verify its effectiveness.

A Self-Decoupling Technique to Realize Dense Packing of Antenna Elements in MIMO Arrays for Wideband Sub-6 GHz Communication Systems.

A self-decoupled technique is described that enables the radiating elements in the antenna array to be densely packed for multiple-input multiple-output (MIMO) wireless communications systems. High isolation between the adjacent antenna elements is obtained by fixing the radiating elements in an orthogonal configuration with respects to each other. Current from the adjacent ports cancels their impact which results in low mutual coupling. The additional benefit of this configuration is realizing a densely packed array. The ground plane of each radiating element on the array board itself are isolated to mitigate surface wave propagations to suppress mutual coupling between the antenna elements. The radiating elements are based on a modified edge-fed circular patch antenna that includes a curved slot line and open-circuited stub to widen the array's impedance bandwidth with no impact on the antenna's footprint size. The proposed technique was verified with the design of an antenna array of matrix size 4 × 4 centered at 3.5 GHz. The array had a measured impedance bandwidth of 4 GHz from 1.5 GHz to 5.5 GHz, which corresponds to a fractional bandwidth of 114%, peak gain of 3 dBi and radiation efficiency of 84%. Its average diversity gain and envelope correlation coefficient (ECC) over its operating band are 9.6 dB and &lt;0.016, respectively. The minimum isolation achieved between the radiating elements is better than 15 dB. The dimensions of the array are 0.4 × 0.4 × 0.039λ_g^3. The proposed array has characteristics suitable for sub-6 GHz wireless communication systems.

Near-Field Millimeter-Wave Imaging via Multi-Plane MIMO Arrays

Multiple-input multiple-output (MIMO) array-based millimeter-wave (MMW) imaging has broad application prospects in concealed weapons detection due to its capability of high resolution at a reasonable cost. This paper presents a novel multi-plane MIMO array topology for near-field MMW imaging. The multi-plane MIMO arrays can offer wider angular observations of the target under test than the traditional planar MIMO arrays. Although the cylindrical MIMO array can achieve similar focusing performance as the multi-plane one, the multi-plane MIMO arrays are much easier to fabricate since each subarray has the same structure as a planar one. In addition, to speed up the image reconstruction process, we propose a corresponding three-dimensional (3-D) imaging algorithm with hybrid processing in the time-domain and wavenumber-domain. The proposed algorithm is even more efficient than the wavenumber-domain algorithm for the cylindrical MIMO array that has the same scale as the proposed multi-plane array scheme, which clearly shows that the hybrid time-wavenumber domain processing can avoid the enormous computation burdens of higher dimensional processing of the wavenumber-domain MIMO imaging algorithms. Numerical simulations and experimental results are provided to demonstrate the superiority of the proposed multi-plane MIMO array imaging technique in comparison with the most commonly used arrays and algorithms.

Enhanced Automotive Sensing Assisted by Joint Communication and Cognitive Sparse MIMO Radar

Automotive radar is mandated to provide high accuracy direction of arrival (DOA) estimation for safe driving, while remaining a low cost device for feasible mass production. Sparse multiple input multiple output (MIMO) arrays emerge as a primary candidate to meet these requirements. As DOA estimation accuracy is a main indicator of tracking performance, Cramer Rao Bound (CRB) is chosen as the goodness measurement for sparse MIMO array optimization, but its application requires prior information of the road environment. We propose a cognitive sparse MIMO array automotive radar, which “perceives” the road environment via automotive sensing supplemented by co-existed communication from roadside unit to vehicle (R2V). This information is used for co-designing a sparse MIMO array for enhanced automotive sensing and vehicle to roadside unit (V2R) communication. Note that both static RSU and dynamic RSU are usually deployed in Internet of Vehicles (IoV), which can provide continuous transmission coverage and permanent connectivity. The bi-directional communications are integrated into the automotive radar. This is achieved by joint transmit waveform design with spectral nulls for communications and with shared sparse MIMO array co-design for both sensing and high quality V2R communications. Simulation results validate the enhanced automotive sensing performance assisted by the integrated bi-directional communications in the cycle of cognitive-driven optimization.