MIMO Antennas for Wireless Communication

Theory and Design

Leeladhar Malviya, Rajib Kumar Panigrahi, M.V. Kartikeyan

• Publisher: CRC Press
• Year: 2020
• ISBN:
  9781000294972
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Electrical Engineering & Telecommunications
• Index: Technology & Engineering

The desired objective of this book is to investigate diversity and mutual coupling effects on MIMO antenna designs for WLAN/WiMAX/LTE applications, controlled with diversity and ground modification techniques including equivalent circuit diagrams. Diversity techniques in MIMO antennas leading to the performance improvement ratings are demonstrated and deliberated. The book contributes towards the development of 2: 1 VSWR MIMO antennas with diversity techniques for indoor/outdoor applications for high data rate, QOS, and SNR. The improved MIMO antenna structures are investigated and presented in this book including part of massive MIMO to provide the important aspects of emerging technology. Aimed at researchers, professionals and graduate students in electrical engineering, electromagnetics, communications and signal processing including antenna theory and design, smart antennas, communication systems, this book:

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• Investigates real time MIMO antenna designs for WLAN/WiMAX/LTE applications.

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• Covers effects of ECC, MEG, TARC, and equivalent circuit.

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• Addresses the coupling and diversity aspects of antenna design problem for MIMO systems.

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• Focus on the MIMO antenna designs for the real time applications.

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• Exclusive chapter on 5G Massive MIMO along with case studies throughout the book.

1

Introduction

In the modern scenario, wireless communication is the most demanding and fastest extending application. Last decade witnessed the exponential growth of wireless applications like multimedia, voice over internet protocol (VoIP), bandwidth/video on demand (BOD/VOD), automatic traffic signaling in industry, research, smart home appliances, and personnel services. Hence, researchers and industrialists are attracted to produce portable and compact radio frequency (RF) devices on large scale. Certain applications like mobile phone and bluetooth have become the essential need of wireless users. The physical layer of internet protocol (IP) i.e. IPv4, IPv6 etc., uses the RF antennas to accomplish duplex communication for continuous, reliable, and dedicated links. Multiple-input multiple-output (MIMO) antenna technology has evolved as an essential part of fourth and fifth generations of wireless applications due to its advantages over a single radiating element on low cost printed circuit boards (PCBs). Involvement of MIMO antennas leads to the high data rate, low power consumption, spectrum saving, large capacity, and better quality of services (QOS) in non-line-of-site (NLOS) communication. MIMO antennas have a lot of capabilities and qualities but are highly affected by the correlation of closely packed radiators, which is one of the challenges in MIMO antenna designs.

1.1 Fundamentals of MIMO Antennas

Modern wireless and mobile applications with low cost and lightweight antennas are integrated within the microwave circuits. MIMO consists of microstrip patch antennas (MPAs) and is implemented on a PCB with a thin layer of perfect electric conductor (PEC) over the dual sides of the dielectric substrate like FR-4 and Rogers RT etc.

MPA is a physical layer radiating product and an essential part of duplex communication [1, 2]. MPAs have been utilized in both civil and military applications due to low cost, light weight, low volume, multi-banding, and easy integrability with microwave components [3, 4, 5, 6, 7, 8, 9, 10, 11]. On the other hand, MPAs have limited bandwidth, low power handling, polarization disparities, and low gain capabilities [12]. Thick substrates may produce large bandwidth and high efficiency, but at the cost of power loss due to surface wave generation [13].

MIMO antenna technology offers required data rates for base station (BS), automobile, pedestrian, satellite, and radar applications. Modern and smart technologies with MIMO antenna systems are reported for wireless local area network (WLAN) licensed/unlicensed bands, wireless inter-operability for microwave access (WiMAX) bands, global system for mobile communication (GSM), long-term evolution (LTE), global positioning system (GPS) applications, 5G, and future generations, etc. [14, 15].

MIMO system came in light due to limitations of single input single output (SISO) system. The Gigabit per second (Gbps) data rate with SISO requires very large-frequency spectrum and is even unable to cooperate in NLOS networks. Also, SISO requires a very large signal to noise ratio (SNR) in practical receivers. Achieving average signal to interference with noise ratio (SINR) > 10 dB is very critical in SISO, even with spectral efficiencies ≥4 bits/s/Hz. Also, due to the power constraint, high gain SISO results in scattering and is unable to assist in NLOS. Extending bandwidth in SISO to achieve Gbps data rate limits the range and reduces fade margin. Hence, large power is required for large coverage. SISO has a range reduction of three times in comparison with modern wireless devices. Frequency reuse plan using SISO requires greater than five times link bandwidth in modern wireless systems [16, 17, 18, 19].

Wireless and mobile applications have witnessed considerable progress from analog communication (first generation) to the digital communication (4th generation). Main challenges with modern antenna designs are space, interoperability, multi-banding, specific absorption rate (SAR), and hearing aid capability (HAC). Variable data rate, high capacity, and scalable bandwidth are few other essential requirements in digital communications at the base and mobile stations. MIMO antenna behavior is characterized by far-field gain, diversity gain (DG), envelope correlation coefficient (ECC), total active reflection coefficient (TARC), mean effective gain (MEG), effective diversity gain (EDG), capacity, and antenna efficiency [20]. MIMO analysis and modeling are essential, irrespective of the type of channel [21, 22, 23, 24, 25, 26, 27].

Modern MIMO designs are concerned with wireless setups for indoor/outdoor activities with different mediums. Hence, site planning, polarization, number of radiators, size/volume of PCBs, angle diversity, compactness, current coupling, and their control must be investigated very carefully [28, 29, 30, 31]. Modern research is better concerned with MIMO antennas in multipath propagation with improved features.

MIMO with limited space and large number of radiators takes care of performance over the wireless environment. There is no space constraint at the base station to accommodate large number of radiators due to multiple wavelength (λ) separation between antennas. Whereas, ≤0.5⁢λ is available in mobile and portable devices. Sufficient space is available even for laptops, personal digital assistants (PDAs), and some other portable devices to make them uncorrelated. Diversity and space reduction techniques limit the space requirement and improve the performance of MIMO applications [32].

Various diversity techniques take care of signal continuity, link reliability, QOS, and coverage in a particular direction etc. Space, pattern, and polarization diversity techniques are generally used in practice. Space diversity is very easy and completely depends on space variation between radiators. Space diversity can easily be implemented at the base stations due to large space available between the radiators. Due to limited space, space diversity is not beneficial at the mobile station and demands large size of implementation. Polarization diversity on the other hand takes care of signals in vertical and horizontal directions. Placement of radiators in orthogonal position ensures required isolation and reduces the overall size of the implementation. Similarly, pattern diversity takes care of unending signaling in desired directions by creating various far-field radiation patterns. It contributes complementary field patterns for properly implemented MIMO designs.

Linearly polarized antennas are easily affected by polarization changes. In cases where polarization is not sure, circularly polarized antennas are required to limit polarization losses and maintain the link reliability. Various diversity techniques can be combined with de-correlation techniques to improve MIMO design parameters.

1.2 Motivation and Scope

Huge demand for MIMO antennas has attracted researchers, academicians, and industrialists. Various wireless technologies have been integrated with MIMO technology to enhance data rates, capacity, and to limit bandwidth and power in NLOS communication. MIMO satisfies the modern need of variable data rates and scalable bandwidth for each wireless application. However, due to limited space, the issue of mutual coupling requires special attention. Diversity and mutual coupling reduction techniques are therefore required.

There is not much complexity and requirements for 2×1 radiating elements on PCB. Only two elements are coupled in this case. However, 2×2 MIMO designs have four radiators and a number of mutual coupling paths. Therefore, strong MIMO designs are required to control the coupling and to enhance design parameters.

Therefore, wireless and mobile engineers are trying their best for efficient and advanced MIMO antenna designs like massive MIMO to satisfy variable Gbps data rates and large capacity. This fact motivated to take up these problems for the enhancement of MIMO antenna performance and to take up this research of using diversity techniques for achieving the same.

The main idea of our book is to bring awareness to researchers in the field of MIMO and massive MIMO antennas. The following points are observed in a thorough investigation of MIMO antenna designs:

1. A number of MIMO designs are available; however, achieving high isolation, compact size, high gain, low ECC, effective active bandwidth, and low MEG in a single MIMO antenna design is still a challenge.
2. Coverage of most of the WLAN/WiMAX bands is mostly limited to 2×1, due to large complexity with 2×2 MIMO antennas available for wireless communication. Increase in the number of data streams makes the analysis and processing very complex.
3. Very few MIMO antennas with circular polarization have been reported in the literature. Simultaneously, achieving compactness with high isolation in circularly polarized MIMO antennas is still a challenge.
4. Always using mutual coupling reduction techniques is not the best solution. Therefore, diversity effects have been utilized and such shapes are generated, which leads to desired outcomes in terms of mutual coupling and size.

The following investigations are undertaken for the performance enhancement of MIMO antennas with different diversity techniques:

1. To elaborate 2×2 compact MIMO antenna design methodology with diversity technique for low mutual coupling for WLAN/WiMAX wireless communication.
2. To explore and develop the design methodology of 2×2 compact MIMO antenna for wide bandwidth with link reliability and low mutual coupling for wireless systems.
3. To develop the design approach of 2×2 MIMO antenna with circular polarization technique with low mutual coupling for WLAN application.
4. To develop the design method of compact 2×2 MIMO with low mutual coupling for long-term evolution applications.
5. To design and develop MIMO antennas with power divider arms and diversity effects for wireless applications.

1.3 Organization of the Book

This book is divided into twelve chapters including the present chapter and is organized as follows:

In Chapter 1, fundamentals of MIMO, the motivation of research, research objectives, problem statement, and the organization of book are discussed in det...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Dedication
• Contents
• Preface
• Acknowledgments
• Symbols
• 1 Introduction
• 2 Theory of MIMO
• 3 Applications of MIMO
• 4 MIMO Antenna Performance Criteria
• 5 5G Massive MIMO Technology
• 6 Mutual Coupling Reduction Techniques MIMO Designs: An In-Depth Survey
• 7 Design and Analysis of Multi-Band Printed MIMO with Diversity and PSG
• 8 Design and Analysis of Wide-Band MIMO Antenna with Diversity and PEG
• 9 Design and Analysis of CP-MIMO Antenna for WLAN Application
• 10 MIMO Antenna Designs with Diversity for LTE Applications
• 11 MIMO Antenna Designs for WLAN/WiMAX Applications with 1 × 2 Power Divider Arms
• 12 Concluding Remarks and Future Perspective
• Bibliography
• Index