In the past six years or so, the number of scientific articles and conference papers providing possible multiple-input, multiple-output (MIMO) antenna system solutions has noticeably increased. Flagship conferences on antennas and propagation have recently had multiple sessions addressing MIMO antenna systems and their applications. The importance of such antenna systems lies in the magnitude of their application in current wireless devices and gadgets, and this thrust will continue because fourth-generation (4G) and the upcoming fifth-generation (5G) wireless standards rely heavily on MIMO technology. But throughout the years, and up until now, a wide range of publications still suffer from some major misconceptions and unclear understanding of the fundamental aspects while designing, characterizing, and evaluating such multiantenna systems.

Current Misuses and Future Prospects for Printed Multiple-Input, Multiple-Output Antenna Systems [Wireless Corner]

Multi-antenna design in compact mobile handsets at frequency bands below 1 GHz is very challenging, since severe mutual coupling is commonly induced by simultaneous excitation of the chassis' fundamental dipole mode by more than one antenna element. To address this problem, a novel multi-antenna design approach is proposed herein to obtain efficient and uncorrelated antennas. By manipulating the chassis structure, more than one characteristic mode is enabled to resonate at frequencies below 1 GHz. With proper excitations for different characteristic modes, which are orthogonal to each other, well matched multi-antennas with low coupling and correlation are achieved. A chassis loaded with two T-shaped metal strips above its longer edges is taken as an example modification to illustrate the effectiveness of the proposed design approach at 900 MHz. This modification creates a new characteristic mode which resonates near 900 MHz. Afterward, two antenna feeds were designed to efficiently excite the chassis' fundamental dipole mode and the T-strip mode with very low correlation. The T-strip antenna covers LTE Band 8 (880-960 MHz), and the dipole mode antenna covers both LTE Band 5 (824-894 MHz) and LTE Band 8. The proposed dual-antenna design was found to outperform a reference design significantly, both with and without user interactions (i.e., one-hand and two-hand data grips). Practical aspects of mobile handset antennas are also investigated. The prototype was also fabricated and measured, and the measured results show reasonable agreements with the simulated results.

/pdf/design-of-orthogonal-mimo-handset-antennas-based-on-2a1ef9srxe.pdf

Design of Orthogonal MIMO Handset Antennas Based on Characteristic Mode Manipulation at Frequency Bands Below 1 GHz

A double-layer mushroom structure is proposed to enhance the interelement isolation of a four-element antenna system, wherein four closely positioned substrate-integrated cavity-backed slot (SICBS) antenna elements are configured for multiple-input multiple-output (MIMO) applications. A wall with a double-layer mushroom structure is positioned in between the four antenna elements. An antenna prototype with a ground plane size of ${\mathbf{0}}.{\mathbf{96}}\;{{\mathbf{\lambda }}_{\mathbf{0}}} \times 0.96\;{{\mathbf{\lambda }}_{\mathbf{0}}}$ ( ${{\mathbf{\lambda }}_{\mathbf{0}}}$ is the free space-wavelength at 2.4 GHz) demonstrates an enhanced interelement isolation of 16 dB for parallel-directed antenna element pairs, while the isolation of the orthogonally directed antenna element pairs remains unchanged over the operating bandwidth ( $\vert {{\mathbf{S}}_{{\mathbf{11}}}}\vert ) of 2.396 –2.45 GHz. With the enhanced isolation larger than 42 dB between each antenna element pair, the envelope correlation coefficient (ECC) is lower than 0.02 across the operating bandwidth. The simulated and measured results validate the good MIMO diversity performance of the proposed antenna system.

Enhanced Isolation of a Closely Spaced Four-Element MIMO Antenna System Using Metamaterial Mushroom

The reduction of mutual coupling between closely spaced antenna elements is attractive in the electromagnetic and antenna community. An efficient approach to suppress the mutual coupling between microstrip patch antennas is proposed using waveguided metamaterials. The waveguided metamaterials are designed and realized by crossed-meander-line slits, which exhibit magnetic resonances and further the band-gap property. By inserting the waveguided metamaterials between two H-plane coupled rectangular patch antennas with the edge-to-edge distance less than λ0/8, about 6 dB reduction of mutual coupling throughout the -10-dB bandwidth has been achieved, which is verified by measurement results.

Reduction of Mutual Coupling Between Closely Packed Patch Antennas Using Waveguided Metamaterials

Multiple input multiple output (MIMO) antenna is at core of the presently available wireless technologies. The design of MIMO antennas over a limited space requires various approaches of mutual coupling reduction, otherwise gain, efficiency, diversity gain, and radiation patterns will be severely affected. Various techniques have been reported in literature to control this degrading factor and to improve the performance of the MIMO antennas. In this review paper, we have carried out an extensive thorough investigation of diversity and mutual coupling (correlation) reduction techniques in compact MIMO antennas.

MIMO antennas with diversity and mutual coupling reduction techniques: a review

A compact planar multiple-input-multiple-output (MIMO) antenna system of four elements with similar radiation characteristics is proposed for the whole 2.4-GHz WLAN band. It consists of two proximity-coupled fed microstrip square ring patch antennas and two microstrip slot antennas of the same linear polarization. These two types of antennas are printed on different sides of the substrate to reduce mutual coupling. With a novel isolation structure etched on the ground plane of the FR4 substrate, high port isolation (below dB) and good MIMO performance are achieved. The overall lateral size of the MIMO system is only , and good impedance matching ( dB) is achieved across the operating band for all the antenna elements. Full spherical radiation patterns are measured for the MIMO system, showing similar radiation characteristics, and the gains are above 2.3 dB across the operating band.

A Compact Planar MIMO Antenna System of Four Elements With Similar Radiation Characteristics and Isolation Structure Hui Li, Student Member, IEEE, Jiang Xiong, Student Member, IEEE, and Sailing He, Senior Member, IEEE

Peer Review #2 of "Comparison of gut microbiome in the Chinese mud snail (Cipangopaludina chinensis) and the invasive golden apple snail (Pomacea canaliculata) (v0.1)"

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A Compact Planar MIMO Antenna System of Four Elements With Similar Radiation Characteristics and Isolation Structure Hui Li, Student Member, IEEE, Jiang Xiong, Student Member, IEEE, and Sailing He, Senior Member, IEEE

Peer Review #2 of "Comparison of gut microbiome in the Chinese mud snail (Cipangopaludina chinensis) and the invasive golden apple snail (Pomacea canaliculata) (v0.1)"