MIMO Antenna Array Research Articles

Compact 4 × 4 UWB‐MIMO antenna with WLAN band rejected operation

A compact planar UWB-MIMO antenna array with WLAN band rejection is presented. The array consists of four monopole radiators and a common ground plane. These monopoles are placed in such a way that the polarisation diversity of nearly placed radiators is exploited, resulting in high isolation. The proposed MIMO antenna array is electrically small (50 × 39.8 mm2), printed on a low loss 1.524 mm thick Rogers TMM4 laminate with a dielectric constant of 4.5 and a loss tangent of 0.002. A band-stop design was inserted on the ground plane to behave similar to a LC band-stop filter and reject the WLAN band. Simulation and measurement results satisfy the return loss requirement of better than 10 dB and isolation better than 17 dB over the entire 2.7–5.1 and 5.9–12 GHz bandwidths.

Mimo circular polarization array antenna with dual coupled 90° phased shift for point‐to‐point application

ABSTRACTThis article presented a circle‐segmented multiple‐input‐multiple‐output (MIMO) circular polarization (CP) array antenna with dual coupled 90° phased shift for 5.8 GHz Point‐to‐Point application. Convergence of CP capability within MIMO array antenna is successfully realized by two array of four circular‐segmented patch array radiating element that are fed by two RF ports. The MIMO CP array antenna with high gain performance is obtained through the dual coupled 90° phased shift that is connected to each circle‐segmented patch. The dual coupled 90° phased shift ensure the E‐field of circle‐segmented patches function is in 90° phase difference to the initial signals. Similarity between azimuth and elevation plane with axial ratio of 1.9 dB verified the proposed antenna's CP capability. In the mean time, correlation coefficient (ρ) of 1.2015 e − 4, diversity gain (Gapp) of 9.9999, S21 of −45.1 dB show the good isolation quality of the antenna in MIMO structure. The gain of 14.6 dB for each port is also recorded. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:809–814, 2015

A MIMO Reversed Antenna Array Design for gsm1800/td-scdma/lte/wi-max/wiLan/wifi

A triband MIMO antenna used for gsm1800/td-scdma/lte/wi-max/wiLan/wifi has been proposed in this paper. The design with the size of 32 m∗73.6 mm is fabricated on FR4 substrate (thickness is 1.6 mm). This antenna consists of two reversed monopole meandered radiators and defected ground structure which work together to achieve impedance match and enhance isolation for all operating bands. According to the subsequent measured results, the working frequency domains are at gsm1800 (1.71 GHz–1.88 GHz), td-scdma (1.88 GHz–2.025 GHz), lte (2.1–2.35, 2.48–2.51), wi-max (3.5 GHz, 5.5 GHz), wiLan (5.725 GHz–5.8 GHz), and wifi (5.8 GHz–5.88 GHz) approximately. Besides, the measured radiation patterns (gain total) are also well at these working frequency domains and the omnidirectional performance has been achieved for the reversed MIMO antenna array. Furthermore, the realized isolation is more than 15 dB, 24.2 dB, and 22 dB at the first, the second, and the third working frequency band, respectively.

Novel Base Station MIMO Antennas with Enhanced Spectral Efficiencies Using Angular Reuse

The true polarization diversity (TPD) technique is combined with the spatial diversity technique in novel MIMO antenna array geometries with a large number of elements. The use of a large number of elements requires some angular reuse within the array for polarization diversity. With designs compatible with existing base station antenna array configurations, the novel geometries with combining diversity schemes are shown to be able to achieve near the maximum spectral efficiencies. True polarization diversity (TPD) schemes are found to be an excellent complement to more conventional spatial diversity schemes for obtaining optimum MIMO array performance in base station antennas.

Circularly polarized MIMO antenna array for point‐to‐point communication

ABSTRACTA compact circularly polarized multiple input multiple output (CP‐MIMO) array antenna for point‐to‐point communication is proposed in this article. The two by four‐element antenna array, dimensioned at 58 × 110 mm2 is composed of rectangular‐shaped with corner‐truncated radiating elements. The presented antenna is developed by two MIMO element with circular polarization characteristics aims to boost gain, more robust to adverse weather conditions and less signal's reflection. By constructing eight 45° truncated edges of 2.45 mm, 45 mm element spacing of Y‐axis, and 39.5‐mm element spacing of X‐axis together contribute to the circular polarization capability of 2.24 axial ratio, 0.00031024 correlation coefficient, and 10 dB diversity gain. The CP‐MIMO antenna which is fed by two coaxial feeds has produced the gain up to 14.25 dB with reflection coefficient of −24.5 dB. Thus, combination of circular polarization, high gain, and excellent MIMO characteristics collectively lead the proposed CP‐MIMO array antenna to avoid significant attenuated signals under adverse atmospheric condition and propagation issues such as reflection, absorption, phasing, and multipath. The proposed antenna's operating frequency of 5.8 GHz has great potential to be applied in point‐to‐point wireless backbone communication system. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:242–247, 2015

Optimal MIMO array for compressive sensing image formation

Many studies have addressed compressive sensing (CS) theory in recent years, especially the use of CS in radar 2D and 3D image formation. Much of this research suggests that sparse targets can be perfectly reconstructed according to the CS theory. However, most of these studies did not examine the design of antenna array for CS reconstruction of sparse targets. Therefore, this study investigates the design method of the Multiple-input/multiple-output (MIMO) antenna array for reconstructing sparse targets. Based on CS theory, mutual coherence of the dictionary matrix was selected as the criteria for evaluating the MIMO antenna array. The analytical expression of the criteria was derived from the MIMO echo signal. Due to the complex mathematical expression of the criteria, the genetic algorithm was used to find the optimal MIMO antenna array. Finally, a comparative simulation and a Monte-Carlo experiment were performed to validate the proposed optimal solution.

Comparison of Different MIMO Antenna Arrays and User's Effect on Their Performances

ABSTRACTMultiple‐input multiple‐output (MIMO) systems have entailed a great enhancement in wireless communications performances. The use of multiple antennas at each side of the radio link has been included in recent drafts and standards such as WLAN, WIMAX, or DVB‐T2. The MIMO performances depend on the antenna array characteristics and thus several aspects have to be taken into account to design MIMO antennas. In the literature, many articles can be found in terms of capacity or antenna design, but in this article, different types of antenna arrays for MIMO systems are measured in a reverberation chamber with and without a phantom as a user′s head. As a result, the MIMO performances are degraded by the user in terms of efficiency, diversity gain, and capacity. Omnidirectional antennas such as monopoles with high radiation efficiency offer the highest performance for a rich scattering nonline of sight indoor environment. © 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:2039–2043, 2013

Surface Wave and Mutual Coupling Reduction between Four Element Linear MIMO Array Antenna

Surface Wave and Mutual Coupling Reduction between Four Element Linear MIMO Array Antenna

Power and Bit Allocation in On-Body Channels Using MIMO Antenna Arrays

In this paper, power and rate are allocated to each eigenchannel of the multiple-input-multiple-output (MIMO) on-body channel under average transmit power and bit error rate (BER) constraints. Three on-body channels, i.e., the belt-head, belt-wrist, and belt-chest channels, are of interest when adopting either discrete- or continuous-rate schemes. First, the on-body channel is modeled using the joint correlation matrix by taking into account the different propagation mechanisms experienced by the spatial subchannels, then the performance in terms of the spectral efficiency of the simulated channel using the model is shown to be in good agreement with the measurements. Owing to the presence of a line-of-sight (LOS) component, the achievable spectral efficiency of the on-body channels is lower than that of the equivalent Rayleigh channel. Due to its low spatial subchannel correlation, the belt-head channel is shown to offer the best performance in terms of spectral efficiency.

Adaptive Quad-Element Multi-Wideband Antenna Array for User-Effective LTE MIMO Mobile Terminals

An LTE MIMO antenna array, which is adaptive to the effects of the user's body, is presented for mobile terminals. The bands of 750-960 MHz and 1700-2700 MHz are covered with a good efficiency in free space. Three kinds of user effects are studied, namely, “SAM head and PDA hand,” “PDA hand,” and “dual hands.” The array is formed by selecting the best two elements out of four, with the two ports and grounding points of the other two elements open. The user effects on MIMO channel capacity are reduced through the adaptive selection of two optimal antenna elements. The total efficiency, envelope correlation coefficient, and multiplexing efficiency are presented for the three kinds of user effects. In the lower band, the decreased correlation due to the optimal selection improves the multiplexing efficiency. The underlying physical mechanisms and some general rules are discussed. The specific absorption rate (SAR) in the “SAM head and PDA hand” case is studied. Experiments for the three kinds of user effects are also carried out.

Distributed Protocols for Interference Management in Cooperative Networks

In scenarios where devices are too small to support MIMO antenna arrays, symbol-level cooperation may be used to pool the resources of distributed single-antenna devices to create a virtual MIMO antenna array. We address design fundamentals for distributed cooperative protocols where relays have an incomplete view of network information. A key issue in distributed networks is potential loss in spatial reuse due to the increased radio footprint of flows with cooperative relays. Hence, local gains from cooperation have to balance against network level losses. By using a novel binary network model that simplifies the space over which cooperative protocols must be designed, we develop a mechanism for the systematic and computational development of cooperative protocols as functions of the amount of network state information available at relay nodes. Through extensive network analysis and simulations, we demonstrate the successful application of this method to a series of protocols that span a range of network information availability at cooperative relays.

Measurement-Based Evaluation of Vertical Separation MIMO Antennas for Base Station

It is worth noting that the use of vertical separation antenna configuration provides an easy way to form large separation on a single pole. In this letter, the effect of vertical separation multiple-input-multiple-output (MIMO) antenna configurations for base station is investigated by field drive tests. The results show that vertical separation antenna configurations can meet the requirement of spatial multiplexing and provide good MIMO performance. Furthermore, measurements of MIMO antenna arrays were conducted to evaluate the performance of radiation patterns with interaction between antennas. The results show that vertical separation antenna configurations can reduce or avoid mutual coupling between antennas and improve the performance of antenna radiation patterns.

MIMO Array Capacity Optimization Using a Genetic Algorithm

This paper discusses the design of multiple-input-multiple-output (MIMO) antenna systems and proposes a genetic algorithm to obtain the position and orientation of each MIMO array antenna that maximizes the ergodic capacity for a given propagation scenario. One challenging task in the MIMO system design is to accommodate the multiple antennas in the mobile device without compromising the system capacity, due to spatial and electrical constraints. Based on an interface between the antenna model and the propagation channel model, the ergodic capacity is considered as the objective function of the MIMO array optimization. Simulation results corroborate the importance of polarization and antenna pattern diversities for MIMO in small terminals. Our results also show that the electromagnetic coupling effect can be exploited by the optimizer to decrease signal correlation and increase MIMO capacity. A comparison among a uniform linear array (ULA), a uniform circular array (UCA), and a genetic algorithm (GA)-optimized array is also carried out, showing that the topology given by the optimizer is superior to that of the standard ULA and UCA for the considered propagation channel.

A Novel Dual-Band MIMO Antenna Array With Low Mutual Coupling for Portable Wireless Devices

In this letter, a dual-band multiple-input-multiple-output (MIMO) antenna array is proposed for portable wireless devices. The MIMO antenna array consists of two back-to-back monopoles elements with an edge-to-edge distance of 0.096 λ -(λ is the free-space wavelength at 2.4 GHz). A shorting strip and an isolation stub are designed to reduce the mutual coupling between the two elements. The MIMO antenna array has a volume of 15 × 50 × 0.8 mm3. It can cover the WLAN 2.4- and 5.8-GHz bands. The measured isolation values (S21) are lower than - 25 and - 20 dB at the 2.45- and 5.8-GHz bands, respectively. The key design parameters are presented, and the parametric study is performed.

An Envelope Correlation Formula for(N,N)MIMO Antenna Arrays Using Input Scattering Parameters, and Including Power Losses

The scattering parameter formulation for the envelope correlation in an(N,N)MIMO antenna array has been modified to take the intrinsic antenna power losses into account. This method of calculation provides a major simplification over the use of antenna radiation field patterns. Its accuracy is illustrated in three examples, which also show that the locations of the correlation minima are sensitive to the intrinsic losses.

A Survey of Distributed Relay Selection Schemes in Cooperative Wireless Ad hoc Networks

Cooperative communication aims to achieve spatial diversity gain via the cooperation of user terminals in transmission without requiring multiple transceiver antennas on the same node. It employs one or more terminals as relays in the neighbourhood of the transmitter and the receiver, which collaborate in the transmission and serve as a virtual MIMO antenna array. Allowing cooperation in wireless communication engenders new problems related to resource allocation and relay selection. Optimal relay selection is vital for reaping the performance benefit of cooperative communication. It is a challenging task to share channel information in timely and distributed manner and at the same time make optimal selection of relay in a time varying radio environment. This paper presents a comprehensive survey of distributed relay selection schemes for cooperative communication that have been proposed in the literature. We discuss various classifications of relay selection schemes and describe their characteristics and functionality. We then present a qualitative comparison of their performance against a set of representative metrics. Finally, we discuss some of their shortcomings and suggest some research directions.

Compact planar MIMO antenna array with polarisation diversity on single layer

A novel compact and planar MIMO antenna array with polarisation diversity is proposed on a single layer. The proposed array is composed of two orthogonal polarised elements which act as electric and magnetic loop antennas. A high isolation of 20 dB between the two antennas is achieved at 2.3 GHz. The overall size of the array is 38 × 28 mm (i.e. 0.291 × 0.214 λ 0 ). The calculated envelope correlation coefficient is 0.00035.

Envelope Correlation Parameter Measurements in a MIMO Antenna Array Configuration

In a 2 × 2 MIMO antenna array system envelope correlation coefficient “ρ” shows the influence of different propagation paths of the RF signals that reach the antenna elements. The approximated value of this coefficient is based on a simple closed-form equation and also varies from 0 to 1. Quite perfect performance for MIMO applications is achieved when this parameter approximates to zero. In this paper, we evaluate an antenna diversity MIMO system by measuring the envelope correlation coefficient. The corresponding results in our antenna array configurations show that the measured “ρ” has very small values and approximates to zero. This observation indicates quite perfect behavior and performance of our MIMO antenna array system.

Performance of a Multiple HAP System Employing Multiple Polarization

In this paper we address the potential gain of using compact MIMO antenna array configurations in conjunction with HAP (High Altitude Platforms) diversity techniques in order to increase the data rates in HAP communication systems. We will also investigate the effects of spatial correlation and mutual coupling between the separate antenna elements on system performance. Simulation results show that although the capacity is degraded by correlation and mutual coupling, we still achieve significant capacity gain compared to the single HAP case. In addition, we evaluate the performance of the system for different separation angles between HAPs, and determine the optimal separation angle that maximizes the total capacity of the system.

The Influence of Efficiency on Receive Diversity and MIMO Capacity for Rayleigh-Fading Channels

A previously published guideline for MIMO antenna arrays is refuted. The influence of radiation efficiency on diversity gain and MIMO capacity of wireless communications systems is investigated through simulations and measurements using a reverberation chamber. Integrated antennas on a portable device have efficiencies low enough to disallow typical inter-element correlation assumptions. Both diversity gain and MIMO capacity depend on the number of antennas, SNR and efficiency in a complex way. When the efficiency of antennas is considered, certain system capacity losses are predicted and measured. These losses may be recovered through using more receive elements than commonly recommended or through the addition of a smaller number of more efficient antennas.