Multiple-input Multiple-output Operation Research Articles

An easy-to-produce HIS-based MIMO radio altimeter antenna design for aircraft

Purpose The purpose of this study is to design a radio altimeter antenna whose production process is facilitated and can work with multiple-input multiple-output (MIMO) properties to provide space gain on the aircraft. Design/methodology/approach To create an easy-to-produce MIMO, a two-storied structure consisting of a reflector and a top antenna was designed. The dimensions of the reflector were prevented to get smaller to supply easy production. The unit cell nearly with the same dimensions of a lower frequency was protected through the original cell design. The co-planar structure with the use of a via connection was modified and a structure was achieved with no need to via for easy production, too. Finally, the antennas were placed side by side and the distance between them was optimized to achieve a MIMO operation. Findings As a result, an easy-to-produce, compact and successful radio altimeter antenna was obtained with high antenna parameters such as 10.14 dBi gain and 10.55 dBi directivity, and the conical pattern along with proper MIMO features, through original reflector surface and top antenna system. Originality/value Since radio altimeter antennas require high radiation properties, the microstrip antenna structure is generally used in literature. This paper contributes by presenting the radio altimeter application with antenna-reflective structure participation. The technical solutions were developed during the design, focusing on an easy manufacturing process for both the reflective surface and the upper antenna. Also, the combination of International Telecommunication Union’s recommended features that require high antenna properties was achieved, which is challenging to reach. In addition, by operating the antenna as a successful MIMO, two goals of easy production and space gain on aircraft have been attained at the same time.

Compact highly isolated dual-band 4-port MIMO antenna for sub-6 GHz applications

In this work, a compact 4-element multiple-input multiple-output (MIMO) antenna system is presented for sub-6 GHz applications. A modified M-shaped strip is used to form each antenna element in the MIMO system. To improve performance, a rectangular-shaped area is etched on the opposite side of each element in the ground plane. The antenna size is 100 × 60 mm2. Most interestingly, the port isolation is improved by rotating the etched areas and the corresponding radiating elements. This one-of-a-kind approach aided in the development of a highly isolated MIMO antenna with a small footprint. The theory of characteristic modes (TCM) is used to analyze the behavior of rotating the etched areas in the ground of the antenna. The antenna provides significant port isolation above 20 dB, stable radiation patterns, and an outstanding ECC less than 0.01. The design is simple and compact, making it suitable for MIMO operation in handheld devices.

An Isolation Improvement for Closely Spaced MIMO Antenna Using λ/4 Distance for WLAN Applications

An isolation improvement for a closely spaced quad port multiple-input multiple-output (MIMO) antenna for WLAN applications is presented. The proposed antenna consists of four L-shaped monopole microstrip patch antennas with a rectangular slot at the center and truncated edges at the corner of each patch element. Interelement isolation is improved by more than 12 dB by considering the patch size, ground size, and distance between the patch elements. The designed antenna uses λ/4 distance between the patch elements. The slot in each patch improves the bandwidth, and truncated edges at the corner of the patch improve the impedance matching of the antenna. The proposed MIMO antenna is designed with the overall dimensions of 45.5 mm × 45.5 mm × 1.96 mm. The MIMO parameters for the proposed technique, which include envelope correlation coefficient (E.C.C.) are less than 0.5, and the diversity gain (D.G.) is 10 dB, suggesting this antenna’s suitability for MIMO operations. The average peak realized gain (A.P.R.G.) and radiation efficiency (RE) is 2.8 dBi and greater than 80% for the prescribed band of interest. The antenna element is fabricated and tested using microwave analyzer N9917A. The measured result seems to be in good contact with the simulation. The proposed MIMO antenna is well-suitable for WLAN applications.

A quad-port multiple-input-multiple-output system for underlay or interweave cognitive radio

<span lang="EN-US">This paper presents a four-element frequency reconfigurable antenna system that is novel in terms of gathering both underlay and interweave cognitive radio in a single multiple input, multiple output (MIMO) design. Built on a 50×38×0.8 mm3 Rogers RT/Duroid 5880 substrate, this system is constructed of two scanning elements to sense ultra-wide band (UWB) with controllable band notching capabilities and two elements act as communication antennas. Eighteen MIMO modes can be provided depending on the state of the five positive-intrinsic-negative (PIN) diodes in each sensing antenna and the four PIN diodes in each communication antenna. These include a scanning UWB mode, fourteen modes to notch WiMax/Cband/<a name="_Hlk120169348"></a>wireless local area network (WLAN)/Xband/ITU in single/dual/triple/quad band rejection states and three interweave modes where each targeting one of the regions of WiMax/Cband/WLAN. Simulated by CST v.10; results like input reflection coefficient and realized gain verify system's capability to work in each operation mode. Moreover, mutual coupling, envelope correlation coefficient and diversity gain all evidence the performance of the proposed system as a MIMO system. Results, simple and compact profile, wide and flexile range of MIMO operation modes in line with the novelty to handle both underlay and interweave cognitive radio all nominate this system as promising to fulfill the needs of modern wireless communications.</span>

Eight Element MIMO Antenna Array With Tri-Band Response for Modern Smartphones

This article presents an eight-element tri-band Multiple Input Multiple Output (MIMO) antenna system for future handheld devices. The suggested antenna system consists of a main and sideboards. The feed lines are connected on the main board while the antennas are placed on sideboards, two on each side separately. The total dimension of the main board is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$150\times 75$ </tex-math></inline-formula> mm2, and the sideboard is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$150\times 7$ </tex-math></inline-formula> mm2. The antenna resonates at three distinct 5G allocated bands of 3.1-3.7 GHz, 4.47-4.91 GHz, and 5.5-6.0 GHz with impedance bandwidths of 600 MHz, 440 MHz, and 450 MHz, respectively. The antenna system provides pattern and spatial diversity characteristics with radiation and total efficiency of 78% and 62% and peak gain of 5.8 dBi. The MIMO system is fabricated, and the measured results are found to be in good agreement with the simulations. The isolation among radiating elements in all resonating bands is found to be >16 dB. The vital MIMO performance parameters such as envelope correlation coefficient (ECC) is less than 0.2 for any two antenna array meeting the required standard of less than 0.5 alongside the mean effective gain or MEG ratio of any two antenna meeting the required standard of less than 3 dB for power balance and optimal diversity. The Channel Capacity (CC) is found to be 41.1 bps/Hz, approximately 3 times that of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2\times $ </tex-math></inline-formula> 2 MIMO operations.

A Conformal Four-Antenna Module for Capsule Endoscope MIMO Operation

In this article, a four-antenna module in a capsule endoscopy is proposed for multiple-input multiple-output (MIMO) operation to achieve the purpose of real-time transmission of high-resolution images with high data rates. For compactness, the proposed design adopts conformal architecture and fully utilizes the inner wall space of the capsule body to accommodate four antennas in the very limited space of the capsule endoscope. For the availability of MIMO operation, three different technical approaches are used to decouple or improve the isolation between neighboring antenna elements and between diagonal antenna elements. System considerations (interaction between the electronic components and the antenna in the endoscope) and specific absorption ratio (SAR) evaluation are performed to verify the robustness and human safety of the proposed design, respectively. In addition, link margin analysis and MIMO channel parameter studies are carried out to verify the wireless telemetry performance and MIMO operation performance, respectively. Antenna prototypes were fabricated and implanted in minced pork for ex-vivo measurements (S-parameters, gain, and radiation patterns). The measured overlapping impedance bandwidth of the four antenna elements is 120 MHz, which can fully cover the 915 MHz industrial scientific medical (ISM) band. The measured isolation between the neighboring antenna elements and the diagonal antenna elements is better than 20 and 10 dB, respectively. The measured maximum peak realized gain is −18.1 dBi.

Doppler Shift Tolerance of Typical Pseudorandom Binary Sequences in PMCW Radar.

In the context of all-digital radar systems, phase-modulated continuous wave (PMCW) based on pseudorandom binary sequences (PRBSs) appears to be a prominent candidate modulation scheme for applications such as autonomous driving. Among the reasons for its candidacy are its simplified transmitter architecture and lower linearity requirements (e.g., compared to orthogonal-frequency division multiplexing radars), as well as its high velocity unambiguity and multiple-input multiple-output operation capability, all of which are characteristic of digital radars. For appropriate operation of a PMCW radar, choosing a PRBS whose periodic autocorrelation function (PACF) has low sidelobes and high robustness to Doppler shifts is paramount. In this sense, this article performs an analysis of Doppler shift tolerance of the PACFs of typically adopted PRBSs in PMCW radar systems supported by simulation and measurement results. To accurately measure the Doppler-shift-induced degradation of PACFs, peak power loss ratio (PPLR), peak sidelobe level ratio (PSLR), and integrated-sidelobe level ratio (ISLR) were used as metrics. Furthermore, to account for effects on targets whose ranges are not multiples of the range resolution, oversampled PACFs are analyzed.

Leveraging frequency agility of an MIMO antenna cluster with a transmitter IC

AbstractThis paper presents the prototype demonstration where an integrated transmitter circuit drives a mobile handset terminal antenna in order to provide frequency tunability and multiple input multiple output (MIMO) operation across the 0.5–4.5 GHz frequency range. The transmitter implementation incorporates on-chip weighted signal generation, i.e. amplitude and phase scaling to provide sufficient MIMO performance in the low band (700–960 MHz) and in the high band (1.5–4.5 GHz). In the transmitter, two antenna elements are used for MIMO operation in the low band and another two in the high band. The transmitter integrated circuit (IC) is fabricated in a 28 nm bulk CMOS technology with an active on-chip area of 0.2 mm$^2$. A custom antenna measurement procedure is proposed here in order to support and verify active antenna measurements with transmitter IC. A measurement procedure for the transmitter system comprising the transmitter IC and four antenna clusters is developed and discussed in comparison with traditional passive antenna measurements. The measurement results demonstrate that the transmitter IC driving the antenna clusters provides total antenna efficiency of $-6.5$ dB to $-1.5$ dB, and envelope correlation coefficient below 0.4 across the designated frequency bands. The results indicate that the implemented transmitter IC successfully tunes frequency response of the antenna clusters, and enhances the MIMO operation of such mobile antennas.

Enhancing 5G MIMO Core Spectral Efficiency with Higher-Resolution Multi-User MIMO and Multi-Beam Operation

In this article, the evolution of two core multiple-input multiple-output (MIMO) features of the 5G New Radio standardization is described along with their motivations, salient designs, and demonstrated benefits. The first feature enables high spectral efficiency with reduced overhead and complexity in the sub-6 GHz regime by exploiting frequency-domain compression and angle-delay reciprocity inherent in high-resolution precoding codebooks for multi-user MIMO. The second feature, intended for the over-6 GHz regime, facilitates streamlined beam management with greatly reduced signaling overhead and latency as well as improved link reliability in the presence of challenging scenarios such as high mobile speed, large number of analog beams, and unpre-dictable signal blocking. The presented features are the outcome of a five-year work and expected to continue evolving to meet a growing number of challenges from new deployment scenarios.

MIMO Operations in Molecular Communications: Theory, Prototypes, and Open Challenges

The Internet of Bio-nano Things is a significant development for next generation communication technologies. Because conventional wireless communication technologies face challenges in realizing new applications (e.g., in-body area networks for health monitoring) and necessitate the substitution of information carriers, researchers have shifted their interest to molecular communications (MC). Although remarkable progress has been made in this field over the last decade, advances have been far from acceptable for the achievement of its application objectives. A crucial problem of MC is the low data rate and high error rate inherent in particle dynamics specifications, in contrast to wave-based conventional communications. Therefore, it is important to investigate the resources by which MC can obtain additional information paths and provide strategies to exploit these resources. This study aims to examine techniques involving resource aggregation and exploitation to provide prospective directions for future progress in MC. In particular, we focus on state-of-the-art studies on multiple-input multiple-output (MIMO) systems. We discuss the possible advantages of applying MIMO to various MC system models. Furthermore, we survey various studies that aimed to achieve MIMO gains for the respective models, from theoretical background to prototypes. Finally, we conclude this study by summarizing the challenges that need to be addressed.

A compact single element dielectric resonator MIMO antenna with low mutual coupling

Abstract A two-port multiple input multiple output (MIMO) dielectric resonator antenna is proposed where two orthogonally connected feed lines are combined to unite two orthogonally produced modes. The feed lines build a hybrid network. The backplane is defected by a circular defected ground structure (CDGS), which is extended by two rectangular slits placed orthogonally with the input ports. The antenna uses a single ‘H/I’-shaped dielectric resonator (DR) element. It covers frequency spectrum from 7.29 to 10.65 GHz and fulfils the international telecommunication union (ITU) (8–8.5 GHz) and Maritime Radio Navigational (8.85–9 and 9.2–9.5 GHz) application bands. The antenna offers very high port isolation (&gt;18 dB) and diversity properties throughout the whole application band. The antenna also provides circular polarization (AR ≤ 3 dB) in the operating ranges from 8 to 8.25 GHz and 8.85 to 8.9 GHz. Simulated and measured results make clear to the antenna most suitable for MIMO operation.

A Novel 2.4-GHz Low-Profile Smart MIMO Antenna with Reconfigurable Frequency-Selective Reflectors

In this paper, a new low-profile smart multiple-input multiple-output (MIMO) antenna system is presented for WiFi IEEE 802.11a/b/g/n/ac/ax applications. The proposed compact 2.4-GHz antenna system employs two beam-switching antenna cells for MIMO operation. Each antenna cell is composed of four reconfigurable frequency-selective reflectors (RFSRs) and a one-to-four switching feeding network. The RFSRs are constructed using a one-wavelength metal loop resonator, which functions as a radiating antenna or a wave reflector to reflect beams along a specific direction, as controlled by the switching network. The feeding switching network utilizes PIN diodes to adjust the phase and impedance required for changing the operational status of each RFSR. The overall dimensions of the antenna system, including the metallic ground, are 120 mm ´ 120 mm ´ 9.5 mm. Moreover, the measured operational bandwidth of the 2.4-GHz antenna is approximately 100 MHz, and the radiation efficiency of each directed beam is 40%–70%.

A Scalable Four-Channel Frequency-Division Multiplexing MIMO Radar Utilizing Single-Sideband Delta–Sigma Modulation

A scalable four-channel multiple-input multiple-output (MIMO) radar that features a modular system architecture and a novel frequency-division multiplexing approach is presented in this article. It includes a single 30-GHz voltage-controlled oscillator (VCO) for the local oscillator signal generation, four cascaded 120-GHz transceivers with a frequency quadrupler, and on-board differential series-fed patch antennas. The utilized uniform antenna configuration results in 16 virtual array elements and enables an angular resolution of 6.2°. The vector modulators in the transmit (TX) paths allow the application of complex bit streams of second-order delta-sigma modulators easily generated on a field-programmable gate array (FPGA) to implement single-sideband (SSB) modulation on the TX signals resulting in orthogonal waveforms for the MIMO operation. Only one phase-locked loop and no digital-to-analog converter is required. The waveform diversity also allows the simultaneous transmission of the TX signals to reduce the measurement time. The application of the SSB modulation on the frequency-modulated continuous-wave MIMO radar requires only half of the intermediate frequency bandwidth compared with the double-sideband modulation. The issue of the phase and amplitude mismatches at the virtual array elements due to the scalable radar architecture is addressed and a calibration solution is introduced in this article. Radar measurements using different numbers of virtual array elements were compared and the digital-beamforming method was applied to the results to create 2-D images.

High-Performance Multiple-Input Multiple-Output Antenna System For 5G Mobile Terminals

In this paper, the systematic design of a multiple antenna system for 5G smartphone operating at 3.5 GHz for multiple-input multiple-output (MIMO) operation in smartphones is proposed. The smartphone is preferred to be lightweight, thin, and attractive, and as a result metal casings have become popular. Using conventional antennas, such as a patch antenna, Inverted-F antennas, or monopole, in proximity to metal casing leads to decreasing its total efficiency and bandwidth. Therefore, a slot antenna embedded in the metal casing can be helpful, with good performance regarding bandwidth and total efficiency. The proposed multiple antenna system adopted the unit open-end slot antenna fed by Inverted-L microstrip with tuning stub. The measured S-parameters results agree fairly with the numerical results. It attains 200 MHz bandwidth at 3.5 GHz with ports isolation of (≤−13 dB) for any two antennas of the system. The influence of the customer’s hand for the proposed multiple antenna system is also considered, and the MIMO channel capacity is computed. The maximum achievable MIMO channel capacity based on the measured result is 31.25 bps/Hz and is about 2.7 times of 2 × 2 MIMO operation.

Unbroken Metal Rim MIMO Antenna Utilizing Antenna Clusters

This letter presents an antenna system for mobile devices with an unbroken metal rim. By utilizing the characteristic mode analysis for the unbroken metal rim, efficient multiple-input–multiple-output operation can be achieved. The design is based on an antenna cluster technique that uses several coupled elements that are used to efficiently excite the modes of the rim. Nonresonant antenna elements and matching networks are used to couple to the metal rim. The design has small ground clearance of 5 mm and height of only 4 mm, and can operate in wide bandwidths both in 700–960 MHz low band and 1.56–4 GHz high band. Measurement results confirm that competent performance is achieved.

Analog Radio-Over-Fiber Supported Increased RAU Spacing for 60 GHz Distributed MIMO Employing Spatial Diversity and Multiplexing

The improvements in coverage through spatial diversity and increased data rates through spatial multiplexing using a distributed multiple-input multiple-output (MIMO) system are important targets for future wireless communications. Here, the appropriate separation of remote antenna units (RAUs) at several user locations in a millimeter-wave system is demonstrated. An analog radio-over-fiber (RoF) fronthaul is used to achieve flexible spacing of distributed RAUs and transports two Gb/s data streams over 2.2 km of fiber and up to 8 m of 60 GHz wireless transmission distance. A performance comparison is performed between single-input single-output and MIMO operation using different antenna spacing and transmission distance. Results show that the wider RAU spacing enabled by the RoF distribution provides improved results at longer distances, for both spatial diversity and for spatial multiplexing. Verification of a method for measuring each channel coefficient individually and using subsequent MIMO processing on these coefficients enables an extension to the results showing the feasibility of 30 m indoor transmission.

Triple‐port, two‐mode based two element cylindrical dielectric resonator antenna for MIMO applications

AbstractIn this letter, a triple‐port multiple‐input–multiple‐output (MIMO) cylindrical dielectric resonator based antenna (cDRA) supporting 2 simultaneous operating modes is presented. The cDRAs are excited by 3 ports supporting MIMO operation. Mode‐1 is an array mode achieved by exciting the 2 element cDRA array via a simple combiner at port‐1. Ports‐ 2 and −3 support individual element excitation via coaxial probes for mode‐2 yielding individual element MIMO operation. The isolation between ports‐1, 2, and 3 is improved by generating orthogonal modes in the cDRA via proper excitation. The isolation between ports‐2 and 3 is improved by etching 2 C‐shaped defected ground structure slits. For all the cases, the isolation between the ports exceeds 20 dB over the operating band. The presented dual‐mode 3‐port MIMO antenna covers the bands between 5.15 and 6.0 GHz.

Extension of an SDR UHF RFID Testbed for MIMO and Monostatic Time of Flight Based Ranging

This paper presents measurement results of a recently introduced time of flight (ToF) ranging method for backscattering radio frequency identification (RFID) tags. The measurements are done with off-the-shelf EPC Class1 Gen2 tags, an automated tag positioner, a modified software defined radio (SDR) platform as RFID reader, and a PC post-processing the ranging results. The structure of the multiple-input multiple-output (MIMO) enabled testbed is shown. A custom FPGA implementation was made to have access to the full potential of the used SDR platform. Furthermore, the synchronization of multiple SDRs to enable MIMO operation is discussed. The ranging error and its variance are measured and discussed for a monostatic ranging enabled RFID reader, using two USRPs. The results are compared to a bistatic setup which uses one USRP only. The underlying ranging principle is successfully verified, and its practical performance limitations, resulting from multipath propagation, are shown.

Dielectric resonator based MIMO antenna system enabling millimetre‐wave mobile devices

In this study, a millimetre-wave dielectric resonator (DR)-based multiple-input–multiple-output (MIMO) antenna system based on two linear arrays is presented. Each array that represents a single MIMO antenna consists of four cylindrical DR antenna (cDRA) elements operating at 30 GHz with a bandwidth of at least 1 GHz. Each array is designed with a fixed beam direction which is tilted to provide low field correlation. A passive microstrip-based feed network was designed to achieve this beam tilting enabling suitable magnitude and phase excitation of the individual cDRAs for radiation. The complete antenna system was designed on a two-layer substrate occupying 48 mm × 21 mm. Excellent field correlation values were measured (below 0.002) across the band of operation while peak gains were >7 dBi. High radiation efficiency is obtained. The proposed design approach for beam tilting, which enables MIMO operation, may also be useful for other compact implementations to support 5G communications.

Four LTE low‐band smartphone antennas and their MIMO performance with user's hand presence

ABSTRACTOwing to the narrow regions along the four edges of the modern smartphone, especially the two narrow regions along the long (side) edges thereof, it has been a design challenge to embed the internal antennas therein. The design challenge is especially critical for embedding the long‐term evolution (LTE) low‐band antennas with operating frequencies below 1 GHz. In this study, based on the open‐slot antenna structure, the design of four LTE low‐band antennas, respectively, disposed along the four edges of the smartphone are presented. The two antennas along the two short (top and bottom) edges have a low profile of 10 mm and can cover 698–960 MHz. The two antennas along the two long edges have a low profile of 1 mm only and can cover 824–960 MHz. The four antennas can be applied in a 4 × 4 multiple‐input multiple‐output (MIMO) system in the 824–960 MHz band (e.g., the LTE band 5 and 8). Conversely, the two short‐edge antennas can be used for 2 × 2 MIMO in the 698–960 MHz band (e.g., the LTE band 5, 8, 13, and 17). The operating principle and antenna performance of the four antennas are presented. The obtained channel capacities for 4 × 4 MIMO and 2 × 2 MIMO operations are also shown. Effects of the user's hand holding the smartphone with the four antennas therein are also analyzed. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:2046–2052, 2016