Multiport Single Element Mimo Antenna Systems

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1		NATHIRULLA SHERIFF	--	1389	2023-01-18 08:51:39	\|
2	update references and layout	Amina Yu	-14 word(s)	1375	2023-01-19 01:49:17	\|

This entry is adapted from the peer-reviewed paper 10.3390/s23020747

In response to the increasing demand for voice, data, and multimedia applications, the next generation of wireless communication systems is projected to provide faster data rates and better service quality to customers. Techniques such as Multiple-Input–Multiple-Output (MIMO) and diversity are being studied and implemented to meet the needs of next-generation wireless communication systems. Embedding multiple antennas into the same antenna system is seen as a promising solution, which can improve both the system’s channel capacity and the communication link’s quality. For small handheld and portable devices, embedding many antennas into a single device in a small area and at the same time providing good isolation becomes a challenge.

5G communication multi-element antenna portable devices SISO wideband MIMO parasitic material mutual coupling

1. Introduction

With the explosive growth in users of present and future technology, there is a pressing need to design new compact antenna systems for higher data rate and large bandwidth. Design and implementation of Single-Input Single-Output (SISO) antennas for portable devices are easy and can be easily integrated into the portable systems. However, SISO systems are susceptible to the problems caused by multipath effect and for obtaining higher gain, the size of a SISO antenna should be increased proportionally ^[1]. For antenna to work efficiently at higher data rates in the existing frequency with an improved channel capacity is a great challenge. With the growing demand, designing Multiple-Input Multiple-Output (MIMO) antenna systems is a significant solution ^[2]^[3]. The MIMO systems precisely provide a technique in which multiple independent channels send and receive data concurrently in the same radio channel. The multiple transmit-and-receive antennas used in MIMO technology improve the radio link capacity to attain the multipath propagation. Next-generation wireless communication technology has presented MIMO systems as a feasible solution to solve the data rate limitation problem experienced by SISO systems, due to its multiple antennas’ capability which can also provide better system reliability and increased channel capacity ^[4]^[5]. The MIMO antenna system can enhance the signal quality and the gain of an antenna but leads to complexity in design and an increase in size ^[6]. To attain a required level of signal independence and good isolation in MIMO operation, the multiple antennas should be placed with adequate separation from each other. But for portable devices, this approach would need to be given more space for multiple antennas, as well as additional feedline length ^[7]. The close placement of the antenna elements for MIMO operations can solve the space issue but results in higher mutual coupling among antenna elements.

In this perspective, various isolation techniques and different types of isolation enhancement techniques are found in literature to improve the isolation in various antenna structures which are discussed. Through these techniques, the gain, bandwidth, envelop correlation coefficient (ECC), and efficiency can be enhanced. The antenna diversity technique used in MIMO systems enhances the performance of MIMO systems through multipath fading and co-channel interference reduction ^[8]^[9]. Depending on the requirement, the diversity gain is achieved by employing different methods such as spatial, polarization, and pattern diversities.

Several findings regarding the potential antenna designs suitable for portable devices and small handheld terminals for the MIMO applications have been described in the literature. Existing literatures discussed have presented works on numerous MIMO antenna designs. In all these designs, more than one antenna elements are integrated or etched on single substrate to apprehend a compact MIMO antenna. This occupies more space and hence presents a big challenge in the industrial design process.

The shared radiator with multiport arrangement is a good alternative to miniaturizing the overall size of MIMO antennas. However, due to the difficulties in getting high isolation among connected ports, only a countable number of antenna designs having shared radiators with more than one port are available in literature. Compared to the array designs and separated ports, there is much less focus on common radiator designs with multiple feeding ports. To regulate mutual coupling, these coupled ports with the shared radiator require extra effort. Thus, designing an antenna becomes critical while considering the required parameters suitable for portable devices.

Currently, any related review paper accessible could not be found in the literature which can provide in detail about the shared radiator multiport MIMO antenna systems and their performance improvement techniques. So, herein, there is endeavoured to explore all the multiport MIMO antennas with a shared radiator, presented in recent years in a holistic manner considering their performance-enhancing techniques and aims to address the design issues for the further advancement in the MIMO antenna design as per their application. The main aim here is to provide a comprehensive literature review of multiport MIMO antenna systems having one shared radiator and a comparative study on different multiport-shared radiator antenna designs and the isolation improvement techniques used in these designs. The primary antenna features of shared radiator multiport MIMO antennas such as gain, frequency, mutual coupling, ECC and their applications are reviewed and compared here. In addition, a brief overview of MIMO mathematical concepts and approaches used in these antenna designs for increasing the isolation are also discussed.

2. Mathematical Concepts of MIMO

In this section, the mathematical concepts for MIMO antenna design are discussed ^[10]. Since the MIMO antenna system has multiple antennas at the transmit side (M_t) and receive end (M_r) as shown in Figure 1, the MIMO system capacity (C) can be expressed by Equation (1).

where P_T—total input power,

σ_{n}^{2}

—noise power, H—channel matrix, H^H—Hermitian transpose of channel matrix and I_Mr—identity matrix.

where P_T—total input power,

σ_{n}^{2}

—noise power, H—channel matrix, H^H—Hermitian transpose of channel matrix and I_Mr—identity matrix.

Figure 1. SISO and MIMO Antenna system.

Mutual coupling occurs when antenna elements are placed in closed proximity, which results in isolation reduction thus affecting performance. The envelope correlation coefficient (ECC) is required because the S-parameters such as S₁₂ or S₂₁ measured in between the ports are inadequate to encompass the effect of all S-parameters. The mutual coupling and return loss at the ports can be used to determine ECC, which helps to find the diversity performance of the MIMO antennas ^[11]. The acceptable and standard value of ECC should be less than 0.5 for portable devices. However, the ECC calculation through S-parameters is effective only in case of lossless antenna substrates but in case of lossy antenna substrate, the ECC must be calculated/measured from the antennas’ far-field radiation patterns. In Table 1, the acronyms and their meanings are included.

Table 1. Acronyms.

Acronyms	Meanings
SISO	Single Input Single Output
MIMO	Multiple Input Multiple Output
TARC	Total Active Reflection Coefficient
ECC	Envelop Correlation Coefficient
DG	Diversity Gain
DGS	Defected Ground Structure
DMN	Decoupling and matching network
CDRN	Coupled Resonator Decoupling Network
CSRR	Complementary Split Ring Resonators
ACS	Asymmetric Coplanar Strip
CPW	Co Planar Waveguide
CE	Common Element
PIFA	Planar Inverted-F antenna
iMAT	Isolated Mode Antenna Technology
EBG	Electromagnetic Bandgap
MEG	Mean Effective Gain
WiFi	Wireless Fidelity
UWB	Ultra-Wide Band
LTE	Long-Term Evolution
WiMax	Worldwide Interoperability for Microwave Access

The mean effective gain (MEG) is an important performance parameter and can be defined as the ratio of the mean power received to the mean incident power of the antenna. It is used to calculate the average received signal strength of each antenna ^[12]. Another performance parameter, which is the total active reflection coefficient (TARC) is the ratio of square root of total reflected powers to the total incident powers ^[13]^[14]. The TARC is a function of frequency and is expressed in Equations (2) and (3).

where, [b] = [S][a] and [S] is the antenna’s scattering matrix, vector [a] is the sum of the available incident power at all the ports, vector [b] is the power reflected to the source and a_n, b_n are the nth element of the vector [a] and vector [b] respectively.

Similarly, the antenna Diversity Gain (DG) is a well-known performance parameter used to verify the efficacy of the diversity. It can be defined as the ratio of rise in SNR of mixed signal from a multiple antenna to the SNR from a single antenna in the system. The DG can be calculated using Equation (4).

Like the above parameters, the dielectric substrate permittivity, loss tangent and thickness play an important role in designing the antennas. The efficiency, return loss and gain can also be improved by the proper selection of the dielectric material.

References

Liu, H.; Yang, W.; Zhang, A.; Zhu, S.; Wang, Z.; Huang, T. A Miniaturized Gain-Enhanced Antipodal Vivaldi Antenna and Its Array for 5G Communication Applications. IEEE Access 2018, 6, 76282–76288.
Takahashi, K.; Arai, H.; Ihara, T.; Ishikawa, Y. A study of antenna configuration and channel capacity about MIMO. In Proceedings of the 2015 IEICE Society Conference, Tokyo, Japan, 16–18 September 2015.
Rohani, B.; Arai, H. Enhancing 4× 4 MIMO channel capacity by dual polarized directional antenna. In Proceedings of the IEICE General Conference, Yokohama, Japan, 28–31 March 2016; p. 181.
Nadeem, I.; Choi, D.-Y. Study on Mutual Coupling Reduction Technique for MIMO Antennas. IEEE Access 2018, 7, 563–586.
Roy, S.; Ghosh, S.; Chakarborty, U. Compact dual wide-band four/eight elements MIMO antenna for WLAN applications. Int. J. RF Microw. Comput. Eng. 2019, 29, e21749.
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Seyyedesfahlan, M.; Uzun, A.; Skrivervik, A.; Tekin, I. Wideband Multiport Antennas. Sensors 2020, 20, 6960.
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Mattheijssen, P.; Herben, M.; Dolmans, G.; Leyten, L. Antenna-Pattern Diversity Versus Space Diversity for Use at Handhelds. IEEE Trans. Veh. Technol. 2004, 53, 1035–1042.
Chouhan, S.; Panda, D.K.; Gupta, M.; Singhal, S. Multiport MIMO antennas with mutual coupling reduction techniques for modern wireless transreceive operations: A review. Int. J. RF Microw. Comput. Eng. 2017, 28, e21189.
Votis, C.; Tatsis, G.; Kostarakis, P. Envelope Correlation Parameter Measurements in a MIMO Antenna Array Configuration. Int. J. Commun. Netw. Syst. Sci. 2010, 3, 350–354.
Glazunov, A.A.; Molisch, A.; Tufvesson, F. Mean effective gain of antennas in a wireless channel. IET Microw. Antennas Propag. 2009, 3, 214–227.
ho Chae, S.; il Kawk, W.; Park, S.O.; Lee, K. Analysis of mutual coupling in MIMO antenna array by TARC calculation. In Proceedings of the 2006 Asia-Pacific Microwave Conference, Yokohama, Japan, 12–15 December 2006; pp. 2090–2093.
Fritz-Andrade, E.; Jardon-Aguilar, H.; Tirado-Mendez, J.A. The correct application of total active reflection coefficient to evaluate MIMO antenna systems and its generalization to N ports. Int. J. RF Microw. Comput. Eng. 2019, 30, e22113.

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Nathirulla Sheriff

Sharul Kamal Abdul Rahim

Hassan Tariq Chattha

Tan Kim Geok

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Update Date: 19 Jan 2023

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1. Introduction

2. Mathematical Concepts of MIMO

References