MIMO Operation Research Articles

Wideband Low-Profile Eight-Port Eight-Wave Annular-Ring Patch Antenna Based on Using Eight Dual-Shorted Dual-Resonant Ring Sectors for 8 × 8 MIMO Mobile Devices

A wideband eight-port eight-wave annular-ring (AR) patch antenna for <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$8\times $ </tex-math></inline-formula> 8 MIMO mobile devices is presented. The AR patch antenna is formed into eight dual-resonant 45o-ring sectors to radiate eight very-low-correlated or generally uncorrelated waves for <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$8\times $ </tex-math></inline-formula> 8 MIMO application. Each ring sector is loaded with two shorting pins and excited by a simple probe feed to generate its half- and quarter-wavelength resonant modes at close frequencies to form a dual-resonant wide operating band. Additionally, all 16 shorting pins of the eight ring sectors have a same distance to the patch center, thereby forming a shorting circle to function like a circular metal wall in the AR patch. This makes the surface currents coupled from the excited ring sector to adjacent sectors to be mainly confined inside the shorting circle. Therefore, with the eight probe feeds located outside the shorting circle in the AR patch, enhanced port isolation is obtained. With the proposed design, the eight-port AR patch antenna having a low profile of 1.4 mm (about <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.028\lambda $ </tex-math></inline-formula> at 5.9 GHz) and an outer diameter of 46 mm (about <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.91\lambda $ </tex-math></inline-formula> at 5.9 GHz) can generate eight very-low-correlated waves over a wide band of about 5.9-7.2 GHz (fractional bandwidth 20% based on 3:1 VSWR for mobile device application). Also, the proposed antenna has a back ground plane and is especially suitable for on-metal surface application. The use of a single proposed antenna can be conveniently applied for the mobile device or Internet-of-Things (IoT) device to cover such as 5.925-7.125 GHz for <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$8\times $ </tex-math></inline-formula> 8 MIMO operation in the possible new mobile communication spectrum.

DESIGN OF CONVEX AND CONCAVE DUAL BENT ARRAY FOR 5G LENS ANTENNA SYSTEM

Previous research on the multi-beam system for the fifth generation (5G) application has shown that the number of feed elements of a lens antenna system at the mobile base station is increasing due to the massive MIMO requirements. The design of the array circuits of the 5G lens antenna systems will be more complicated due to the feeding structure, which consists of the power dividers and phase shifters, thus contributing to higher feeding losses. The antenna fabrication process also becomes more complicated. Besides that, the conventional array feed also produces a single radiation beam only. Thus, a large space is needed, where array feed antennas should be arranged to perform wide-angle beam scanning for 5G massive MIMO operation. Therefore, to overcome these issues, this paper uses a bent array configuration as the lens antenna feed to produce bifurcated beam radiation and has a wide beam angle from the feed radiator to the lens edge. Multiple bent arrays are arranged on the lens axis to generate a multi-beam by cylindrical lens antenna. This paper shows a comparison of the bent array in convex and concave configurations. This process investigates the mutual coupling when more than one bent array is arranged as feed radiators. By comparing the arrays in convex and concave structures, it is observed that the convex structure produces a better-bifurcated beam with a smaller middle lobe. The antenna also produces the same bifurcated beam shifting angle, θs for both ports, when s = 4λ is used. It is verified as the optimum spacing value between two bent array structures by the optimization process.

Time Domain Based Compact Dual Band MIMO Antenna System for LTE Smartphone Applications

The design of an eight-port MIMO antenna at the sub-6-GHz(LTE 42/43 and 46)bands for fifth-generation(5G) smartphone is presented. First,based on the Babinet’s principle, a microstrip slope antenna (MSA) is designed from its counterpart complementary structure, microstrip patch antenna (MPA) to operate over the LTE 46 band. The IFAs are additionally equipped with a parasitic radiating element that allows them to operate at the specific three LTE bands,a proposed single antenna, namely RMS, is achieved. For MIMO operation, two antennas are mounted on a practical PCB (100–40). When shifting their location on the PCB, several antenna layouts are tested. Simulated and experimental results are conducted to examine the performance of the designed MIMO antenna. Good isolated, acceptable gain, and efficiency are obtained over the bands of interest which verify the suitability of the proposed system for MIMO smartphone applications.

A Multiband Shared Aperture MIMO Antenna for Millimeter-Wave and Sub-6GHz 5G Applications.

A shared aperture 2-element multiple-input-multiple-output (MIMO) antenna design for 5G standards is presented in this study, one which uses the same radiating structure to cover both the sub-6GHz and millimeter-wave (millimeter-wave) bands. The proposed antenna comprises four concentric pentagonal slots that are uniformly separated from one another. For the sub-6GHz band, the antenna is excited by a single open-end microstrip transmission-line, while a 1 × 8 power divider (PD) connected via a T-junction structure excites the millimeter-wave band. Both the sub-6GHz and mm-wave antennas operate in a MIMO configuration. The proposed antenna design was fabricated on a 120 × 60 mm2 substrate with an edge-to-edge distance of 49 mm. The proposed sub-6GHz antenna covers the following frequency bands: 4–4.5 GHz, 3.1–3.8 GHz, 2.48–2.9 GHz, 1.82–2.14 GHz, and 1.4–1.58 GHz, while the millimeter-wave antenna operates at 28 GHz with at least 500 MHz of bandwidth. A complete antenna analysis is provided via a step-by-step design procedure, an equivalent circuit diagram showing the operation of the shared aperture antenna, and current density analysis at both millimeter-wave and sub-6GHz bands. The proposed antenna design is also characterized in terms of MIMO performance metrics with a good MIMO operation with maximum envelop correlation coefficient value of 0.113. The maximum measured gain and efficiency values obtained were 91% and 8.5 dBi over the entire band of operation. The antenna is backward compatible with 4G bands and also encompasses the sub-6GHz and 28 GHz bands for future 5G wireless communcation systems.

Neutralizing line based triple-band MIMO antenna with polarization diversity for WLAN/C/X band usage

ABSTRACT A four-element multiple-input-multiple-output (MIMO) antenna has been designed to operate at triple wide bands with improved port-isolation and polarisation diversity. The resonant modes of the MIMO are achieved by meander slot-loaded elliptical-shaped fundamental radiators, and the inter-port isolation is achieved by employing neutralising line-embedded ground plane. Apart from port-isolation, the proposed MIMO also offers polarisation diversity at different operating bands. The triple-band MIMO offers linear polarised radiation at WLAN band (4.2–5.6 GHz), right-hand circular polarised (RHCP) radiation at C-band (6.3–7.5 GHz) and left-hand circular polarised (LHCP) radiation at X-band (8.7–9.3 GHz). The overall isolation (>27 dB), envelope correlation co-efficient (ECC<0.0005), diversity gain (DG>9.9995), mean effective gain (MEG<0.734 dB), total active reflection co-efficient (TARC<−20 dB) and channel capacity loss (CCL<0.35 bits/S/Hz) meet the criteria for reliable MIMO operation. The proposed MIMO has been fabricated on a 55.6 × 55.6 × 1.6 mm3 piece of an FR-4 epoxy substrate after simulation and measured in VNA. Adequate similarity can be observed between the measured and simulated results.

Triple-Band Microstrip Patch Antenna and its Four-Antenna Module Based on Half-Mode Patch for 5G 4 × 4 MIMO Operation

To meet the demands of the new frequency bands and the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4\times 4$ </tex-math></inline-formula> multiple-input multiple-output (MIMO) specification brought by fifth generation (5G), a triple-band microstrip patch antenna and its four-antenna module are proposed. Based on the half-mode microstrip patch, the first three modes of TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2,0</sub> , TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2,1</sub> , and TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3/2,0</sub> that can be independently tuned are engineered to cover the three Chinese 5G bands (N41/N78/N79). The proposed triple-band microstrip patch antenna with the volume of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$33.5\times 32.5\times 4$ </tex-math></inline-formula> mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> shows the −6 dB frequency bands of 2.47–2.75 GHz, 3.39–3.60 GHz, and 4.69–5.10 GHz, which makes a nice compromise between antenna volume and impedance bandwidths. Four such patches are arranged in a sequentially rotated style to constitute the triple-band four-antenna module, which is with the volume of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$71\times 71\times 4$ </tex-math></inline-formula> mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> . Measured results of the module show high performance. The reflection coefficients of the four elements are almost identical: the bandwidths are 2.50–2.75 GHz, 3.41–3.62 GHz, and 4.68–5.01 GHz; all the isolations are better than −13.3 dB; the average total efficiencies of the four elements are between −1.41 and −1.11 dB, −2.45 and −2.10 dB, and −1.81 and −1.53 dB for N41, N78, and N79, respectively; and all the envelope correlation coefficients (ECCs) are lower than 0.07.

Low-Profile Six-Port Circular Patch Antenna With Six Triple-Shorted Dual-Resonant 60°-Disk Sectors to Generate Six Uncorrelated Waves for Wideband Mobile MIMO Antennas

A low-profile six-port circular patch antenna generating six uncorrelated waves in a wide band of about 5.8-7.5 GHz (based on 3:1 VSWR, fractional bandwidth about 25%) is presented. The antenna thickness is 1.4 mm (about 0.027&#x03BB; at 5.8 GHz), which includes a 0.4 mm thick FR4 substrate with the circular patch printed thereon and an additional 1.0 mm thick air layer to achieve a low-permittivity antenna substrate. The circular patch with a diameter of 40 mm (about 0.77&#x03BB; at 5.8 GHz) is separated into six 60&#x00B0;-disk sectors by using three linear slots across the patch center and sequentially rotated by 60&#x00B0;. Each disk sector is short-circuited to the ground plane through three properly located shorting pins. It thus makes the 0.5-wavelngth and 0.25-wavelength resonant modes excited at nearby frequencies to form a dual-resonant wide band for each port. Additionally, the six ports in the proposed antenna have their port isolation larger than 10 dB and the corresponding six radiating waves have very low envelope correlation coefficients (less than about 0.02) over the wide band. That is, six uncorrelated waves suitable for MIMO (multi-input-multi-output) operation are obtained. The proposed antenna can find applications for wideband mobile MIMO antennas to cover 6.425-7.125 GHz of the possible new mobile communication band or 5.925-7.125 GHz for the new unlicensed WiFi-6E band.

Frequency Selective Meta-Structure Embedded Two-Element MIMO Antenna with Enhanced Isolation and Pattern Diversity for WLAN/WiMAX Applications

ABSTRACT A two-element MIMO antenna, with improved isolation and pattern diversity, is designed and presented. The dual-band MIMO covers both the adjacent upper WLAN (5.2 GHz) and WiMAX (5.8 GHz) bands with clear isolation between them. The unit radiator of the MIMO is a co-planar waveguide-fed trapezoidal patch that achieves its resonant modes by adjusting the slope of the non-parallel sides. A frequency selective meta-structure is placed in-between the two radiating elements to reduce the mutual coupling and achieve pattern diversity. The MIMO offers peak gains of 1.56 and 5.16 dB at 5.2 GHz (5.1–5.34 GHz) and 5.8 GHz (5.68–5.9 GHz), respectively. The port-isolations achieved at WLAN and WiMAX bands are 26 and 23 dB, respectively. The correlation co-efficient (ECC < 0.05), diversity gain (DG > 9.99) and channel capacity loss (CCL < 0.03) also adhere to the criteria for MIMO operation. The measured results are in good agreement with the simulated ones.

A 28-GHz Beam-Space MIMO RX With Spatial Filtering and Frequency-Division Multiplexing-Based Single-Wire IF Interface

The evolution of mm-wave phased array receivers (RX) to MIMO RX promises multi-beamforming and improved capacity. Although digital beamforming (DBF) provides the highest flexibility, digitization in the beam space as opposed to element space enables ADC digitization scalability with number of beams ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\le $ </tex-math></inline-formula> 4) and spatial filtering prior to the ADC. mm-Wave MIMO arrays must also address the challenge of increased IO routing while supporting dense fill-factors with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda /2$ </tex-math></inline-formula> antenna spacing. In this work, an MIMO beam-space RX array architecture with simultaneous spatial filtering and single wire frequency-domain multiplexing (FDM) is presented. The reconfigurable weighted multi-phase mixing based beam-space RX scheme achieves both: 1) multi-beam formation/spatial filtering and 2) FDM of multiple beam-space outputs, preserving full MIMO field-of-view while ensuring a single IF interface. A 28-GHz four-element RX prototype demonstrates the proposed architecture in 65-nm CMOS. The IC occupies only 3.4 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 3.1 mm for a four-element MIMO 28-GHz array and can form four independent beams with >400-MHz 3-dB BW and FDM on to a single IF interface. The array consumes 450 mW and achieves >27-dB beam-to-beam isolation over 150-MHz BW, while consuming 28.1 mW/stream/beam for 28 GHz. Concurrent MIMO measurements with two wireless 28-GHz beams are shown at 400 Mb/s (100 Msps, 16QAM) data rate demonstrating mm-wave MIMO operation.

Superimposed Pilot for Multi-Cell Multi-User Massive FD-MIMO Systems

In this paper, superimposed pilot based communication strategies are investigated for a time-division duplex (TDD)-based massive Full-Dimension MIMO (FD-MIMO) network jointly considering both uplink (UL) and downlink (DL) performance. To be specific, the DL multi-cell multi-user MIMO operation is connected to UL channel estimation through the superimposed pilot. The performance of UL channel estimation is analytically characterized and the estimated UL channel is linked to the DL MIMO operation for the massive MIMO network. In this way, the corresponding feedback for DL channel state information (CSI) can be eliminated while the UL pilot overhead can be minimized. Results suggest that superimposed pilot could significantly improve the overall network performance of a massive FD-MIMO network.

Coverage Extension of Indoor 5G Network Using RoF-Based Distributed Antenna System

We propose and demonstrate a cascaded distributed antenna system (DAS) for efficiently extending the coverage of the mmWave-based 5G indoor network. For this, we exploit the radio-over-fiber (RoF) system based on the intermediate-frequency-over-fiber (IFoF) transmission technique that is enabled to add/drop the specific wavelength to the designated remote antenna unit (RAU) with using optical splitters and coarse wavelength division multiplexing (CWDM) filters. Moreover, the IFoF transceivers (TRx) perform the subcarrier multiplexing (SCM) in order to transmit 2 × 8 frequency allocation (FA) 5G signals per a single optical carrier, where each FA has 100 MHz bandwidth, leading each RAU to support 2 × 2 MIMO operation. Consequently, the cascaded structure allows for the adaptive and flexible configuration of the order of MIMO in accordance of the required data throughput at the specific indoor area. We introduce the cascaded IFoF link structure that can support up-to 13.5 dB optical power budget with following errorvector-magnitude (EVM) performance characterizations. And then we experimentally demonstrate the RoFbased cascaded DAS network, showing that more than 1 Gb/s total throughput can be achieved per a single antenna. Furthermore, we examine the use of avalanche photodiode (APD) to further increase the optical power budget (i.e., the coverage) based on experiment as well as simulation.

Switch-Reconfigurable Metal Rim MIMO Handset Antenna With Distributed Feeding

A new antenna design method together with a novel metal rim antenna is presented in this paper. The design method transforms an electromagnetic synthesis problem into a circuit problem, which can be solved in a straightforward manner. The new metal rim antenna is based on switches and the antenna cluster concept. The antenna cluster concept uses several, differently fed radiating elements together as one antenna. The proposed method is used to design a handset antenna with small ground clearance of 5 mm capable of 2×2 MIMO operation in the 698-960 MHz low band with 30-40 % efficiency and 4×4 MIMO in the 1.7-2.7 GHz middle-high band with better than 50% efficiency, and the 3-4 GHz high band with efficiency up to 75 %. The proposed optimization method leads to a novel way of distributing the antennas over the entire available volume.

Self‐decoupled compact metal‐frame LTE MIMO antennas for the smartphone

AbstractTwo self‐decoupled, closely‐spaced, metal‐frame LTE MIMO antennas with compact frame lengths to fit in the short edge of the metal‐framed smartphone are presented. The 2 MIMO antennas include a first antenna covering the LTE low band (LB) in 824–960 MHz and LTE middle/high band (M/HB) in 1710–2690 MHz and a second antenna covering the LTE M/HB in 1710–2690 MHz. With a small ground clearance of 5 mm, the first antenna uses a radiating metal frame (frame 1) of length 47 mm to cover the LTE L/M/HB, while the second antenna uses a radiating metal frame (frame 2) of 23.4 mm for the LTE M/HB coverage. In addition, frames 1 and 2 are closely spaced with a gap of 2 mm only. Wideband decoupling between the 2 antennas for the 2 × 2 MIMO operation in the LTE M/HB is obtained with frame 2 serving as an inherent decoupling structure. That is, frame 2 not only functions as a radiator of the second antenna but also serves as a decoupling structure to attract the surface currents on the system ground plane which causes the coupling of the 2 antennas. Applications of applying another 2 MIMO antennas at the opposite short edge of the smartphone for the 4 × 4 LTE M/HB and 2 × 2 LTE LB MIMO operations are also addressed.

A 79-GHz 2 $\times $ 2 MIMO PMCW Radar SoC in 28-nm CMOS

In this paper, the concept of phase modulated MIMO radars is explained and demonstrated with a 28-nm CMOS fully integrated 79-GHz radar SoC. It includes two transmitters, two receivers, and the mm-wave frequency generation. The receivers' outputs are digitized by on-chip ADCs and processed by a custom designed digital core, which performs correlation and accumulation with a pseudorandom sequence used in transmission. The SoC consumes 1 W to achieve 7.5 cm range resolution. A module with antennas allows for 5° resolution over ±60° elevation and azimuth scan in 2 × 2 code domain MIMO operation. A 4 × 4 MIMO system is also demonstrated by means of two SoCs mounted on the same module.

Integrated yet decoupled dual antennas with inherent decoupling structures for 2.4/5.2/5.8-GHz WLAN MIMO operation in the smartphone

Integrated yet decoupled dual antennas with inherent decoupling structures for 2.4/5.2/5.8-GHz WLAN MIMO operation in the smartphone

Efficient evaluation of specific absorption rate for MIMO terminals

Multi-antenna enabled terminal devices are required to comply with the standards for limiting human exposure to electric fields. However, when compared to traditional single-antenna terminals, a comprehensive evaluation of specific absorption rate (SAR) for multi-antenna terminals is impractical. This is because both the power allocation and phase of the electric fields from different antennas are arbitrary in practical MIMO operation, hence requiring exhaustive evaluation over all possible cases. In this context, this paper first proposes time averaged simultaneous peak SAR (TASPS) as an efficient metric to evaluate exposure when more than one antenna is transmitting simultaneously. Then, it is analytically derived that TASPS will be below a given exposure limit, as long as the stand-alone peak SAR for each antenna is smaller than that limit. Thus, SAR evaluation is greatly simplified since only stand-alone SAR needs to be measured. Several examples of dual-antenna mobile handsets are shown to illustrate and validate the analytical result. (Less)

Neutralized Coupling Elements for MIMO Operation in 4G Mobile Terminals

A novel multiple-input-multiple-output (MIMO) dual-antenna system covering the low LTE700 and GSM850/900 communication standards is proposed for mobile terminals. The two-port antenna system is composed of two 3-D coupling elements, placed on the vertices of the short corner of a rectangular FR4 substrate. This rectangular shape emulates the printed circuit board of a modern mobile terminal. To achieve high port-to-port isolation, the neutralization technique is applied. Simulated reflection coefficients, total efficiencies, and envelope coefficient correlation are compared to measured data showing good agreement and competitive performance.

Small-Size Planar LTE/WWAN Antenna and Antenna Array Formed by the Same for Tablet Computer Application

For eight-band LTE/WWAN operation (704–960/1710–2690 MHz) in the Ultrabook or thin-profile tablet computer, a planar antenna of simple structure and small size is presented. The proposed antenna is obtained by modifying a simple planar inverted-F antenna and can be printed on one surface of a thin FR4 substrate of size 10 × 45 mm2 only. The antenna's lower band bandwidth is greatly widened by embedding a proper chip capacitor of 2.7 pF at the feeding strip. This chip capacitor combines with the antenna's shorting strip can control the excitation of a parallel resonance to modify the impedance matching of the antenna's lower band such that a widened bandwidth is easily obtained to cover the LTE700/GSM850/900 operation. Conversely, the antenna's upper-band bandwidth is also greatly enhanced by using a coupled section in the antenna's radiating strip and adding a parasitic shorted strip near the feeding strip, which lead to multiple resonant modes excited to form a wide bandwidth (>1 GHz) to cover the GSM1800/1900/UMTS/LTE2300/2500 operation. Owing to its small size and simple structure, the proposed antenna is very suitable to be applied in achieving an antenna array with high isolation for MIMO or dual talk (dual WWAN) operation. Promising high-isolation antenna arrays formed by the proposed antennas are presented. The obtained isolation between the antennas in the antenna array is better than 12 dB, and the envelope correlation coefficient is less than 0.15 for frequencies over the LTE/WWAN bands. Details of the proposed antenna and antenna array are presented. © 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:1928–1934, 2013

Internal mobile phone antenna array for LTE/WWAN and LTE MIMO operations

AbstractAn antenna array comprising a main antenna for eight‐band LTE/WWAN operation and an auxiliary antenna to combine with the main antenna for LTE MIMO operation in the mobile phone is presented. Both the main and auxiliary antennas are disposed at the bottom edge of the system circuit board of the mobile phone and separated by a protruded ground. The main and auxiliary antennas can respectively fit in two small no‐ground regions of 15 × 30 mm2 and 15 × 20 mm2 on the system circuit board, while the protruded ground in‐between the two antennas has a width of 10 mm for mounting a USB data port. The main antenna covers the 704–960/1710–2690 MHz bands for eight‐band LTE/WWAN operation, and the auxiliary antenna covers the 704–787/2300–2690 MHz bands such that the main and auxiliary antennas together can perform LTE MIMO operation in the LTE700/2300/2500 bands. The proposed antenna array is fabricated and tested. Results are presented and discussed. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26038