1
Introduction

Wireless technology has been evolving and advancing at an astonishing rate over the past four decades. The amount of development and accomplishments that the wireless industry has achieved is beyond imagination, and no one 40 years ago would have predicted the level of advancement we are experiencing nowadays. What is more, new frontiers and developments are underway to even go beyond some of the fundamental laws that have predicted the technology trends thus far. Wireless technology has relied heavily on advancements in electronics, algorithms, and RF front-ends and antenna systems. Moore’s law has been driving the electronics and chip industry for several decades but recently has been overcome by the rapid development of computing power. The need for multi-band, and multi-functional RF front-ends and antenna systems has become a reality nowadays with smaller footprints and higher efficiencies. Our cell phones today have more computing, connectivity, and functionality than complete computers of the past decade.

This rapid technological advancement has been noticeable in every aspect of our daily lives. We are living in smart homes, driving smart cars, using smart phones, and living in smart cities, and these are keeping us aware and connected to our loved ones, assets, and work at any time. Internet coverage is covering more ground with satellite services that are now providing services to remote areas. This has increased the safety aspects of our lives and improved our decision-making and selection capabilities. We can always track our kids, follow up with coworkers, and perform our duties in a much more efficient way that can save a lot of time and effort. The need for more data and connectivity has been increasing exponentially every year (see Figure 1.1), thus pushing the need for rapid improvements on the device and network levels.

Figure 1.1 Global mobile network traffic in Exabytes (EB) per month.

Source: Adapted from Ref. [1].

While a wireless system depends on RF connectivity, fast and efficient hardware and software components, displays, and control devices, the RF front-ends and antenna systems also play a major role in providing a reliable connection with the network. The very first component of the RF front-end is the antenna system. Antennas are the signal converters that convert the electrical signal from the electronics of your device (i.e., your data, whether you are browsing a web page or making a phone call) into an electromagnetic waveform that can travel in the air from your device to the receiving serving station (i.e., a cell phone tower, a wireless local area network access point, or your car radio via Bluetooth). The antenna can transmit your data to the base station, or receive data from the base station (i.e., it is a reciprocal element). Proper design of such antenna systems is essential to having a proper connection in any wireless system.

Antenna systems’ design and development is a combination of science and engineering art. Their characteristics are affected by various parameters such as size, material, shape, surroundings, and types, among many others, and have to be carefully designed and characterized. Careful integration with other system components is critical after the initial design and verification phase is completed to fulfil the expected performance and metrics. While single antenna wireless systems were adopted in the first three wireless generations (i.e., first, second, and third), the fourth generation introduced a new paradigm of wireless communications. It is based on sending multiple data streams to improve the system capacity (data rates) and combat the degradation from multipath signals that exist in all modern environments. This new paradigm is called MIMO communications, which require the existence of multiple antenna systems at the receiver and the transmitter sides. The introduction of multiple antennas in small form factor devices poses serious challenges to make such systems a complete success and achieve the desired high capacity.

This book focuses on the design and engineering of antenna systems for current and future wireless technologies and standards. While the antenna concepts and examples in this book focus on the current 5G requirements and use cases, they are equally applicable to any other wireless standards, as the fundamental aspects of antennas are to be satisfied regardless of the targeted technology. MIMO antenna systems in particular will be given special attention in addition to millimeter-wave (mm-wave) solutions for 5G and beyond.

1.1 Wireless Technology Evolution

While wireless technology evolution is usually associated with different cellular telephony generations, several other factors have driven wireless technology evolution and fast advancement, especially in the past two decades. Among others, additive manufacturing, ultra-scale integration, automation and cost reduction, and fast computing power via the dense integration of processor cores and fabricating nanoscale transistors have contributed heavily toward the level of the technology we have today.

First-generation (1G) cellular technology appeared in the 1980s and relied on the advanced mobile phone system (AMPS) that provided voice-only services to mobile terminals. This was a purely analog technology. The antennas used were whip structures such as helical- or monopole-based ones that protruded from the device. A decade later, technology started to advance more in the digital domain and the global system mobile (GSM) was introduced, resulting in new mobile terminals introduced to the consumer market. It is based on digital techniques that allow the transmission of voice and data (mainly text) with data rates up to 270 kbps. This was considered the second generation of cellular technology (2G). GSM systems were based on time division multiple access (TDMA). Integrated printed antennas started to appear in some models in 2G mobile terminals, at the same time with smaller form factor devices. This is due to the large-scale integration of functionality in the components used.

The addition of multimedia features and incorporation of diversity techniques appeared in the third generation of wireless cellular technology (3G) in the early 2000. Wideband code division multiple access (WCDMA) technology was incorporated and provided wider bandwidths that allowed data transfers in the tens of Mbps. Internet browsing and online gaming became a reality for the first time. International roaming and more secure protocols were utilized. Antenna systems that are or printed fashion were used and multiple functionalities were supported by dedicated antennas, i.e., global positioning system (GPS), wireless local area networks (WLAN), etc.

The introduction of MIMO technology was the driver for 4G. While MIMO was the main focus of 4G, several advancements in modulation and coding and access techniques provided a noticeable capability improvement over 3G that allowed for ultra-fast data transfers in excess of 80 Mbps, making it 20 times faster than its predecessor. MIMO takes advantage of the multipath phenomena that were not very favorable in 3G systems. It creates multiple signal paths that can significantly improve the amount of data transferred within the same frequency band and transmission power levels. Long-term evolution (LTE) networks were built around MIMO technology where multiple antennas on the mobile terminal and multiple antennas in the base station are used to support a communication link. Placing multiple antennas on the mobile terminal is very challenging and needs careful attention to changes in antenna parameters such as isolation and field correlation. These aspects will be discussed in detail in the coming chapters.

The fifth-generation (5G) standard came to provide another leap in connection speeds reaching Gbps levels, with a new paradigm that provides a much broader connectivity framework with three vertices – one focusing on enhanced mobile broadband (eMBB), second providing ultra-reliable low-latency communications (URLLC) that consider fast decision-making features (in autonomous cars for example), and third is the massive machine-type communications (mMTC). For the eMBB which is used for cellular networks, two bands were selected to support 5G requirements; the sub-6 GHz band, also known as frequency range 1 (FR-1), and millimeter-wave band (mm-wave) also called frequency range 2 (FR-2). As there are multiple frequency bands with a large frequency ratio, two sets of antenna systems are expected to support each, in addition to several copies of each to support MIMO. With this, we can imagine how the antenna systems will be packed within a mobile terminal with limited space, and thus this becomes a very challenging problem. This book provides several solutions to 5G-enabled designs. Also, mm-wave bands need antenna arrays with higher gains to overcome the free space path loss (FSPL). Thus, careful integration and array designs with beam steering/switching are required. A summarizing figure that compares the differences in the services and speeds of various wireless cellular generations is shown in Figure 1.2

Figure 1.2 Wireless standard evolution from 1G to 5G and their main features.

Currently, we are thinking beyond 5G or the sixth-generation (6G) wireless standard and its underlying technologies. Key features that are being considered are the use of sub-THz bands for extremely high data transfers of 100 Gbps at short distances, virtual reality (VR) and augmented reality (AR), the...