Preface

With the increasing demand for antennas and narrow beam widths with beam steering capabilities, array antennas have become a wise choice as they offer versatile and flexible solutions for desired radiation patterns. The radiated field of the array depends on the main design parameters, such as the geometrical layout of the elements and their spacings, the excitation in amplitude, and/or phase of the individual elements, and finally the pattern of the individual elements. Many array synthesis techniques that use either analytical or numerical approaches have been extensively employed to improve the radiation pattern of the array. This book addresses recent techniques that aim to improve and optimize the radiation pattern of the array antenna. The book presents a concerted set of issues related to design concepts and methodologies that have recently been proposed to develop and improve the radiation characteristics of antenna arrays.

While most of the array pattern synthesis approaches deal with all of the elements of the array antenna, recent techniques try to offer easier solutions as only a limited number of the elements need to have their magnitudes and/or phases adjusted. Such approaches reduce the cost and complexity of the optimization process by dealing with a small number of selected elements. Whether dealing with all the array elements or a selected number of them, the analytical approaches give better insight and a more explicit way to synthesize the desired pattern. However, global numerical optimization methods have easier and shorter paths towards achieving better performance and optimum results. As the distribution of the power density in the near field of the array is required in some applications, the problem of array synthesis using numerical approaches becomes more desirable than using analytical ways as the latter will involve lengthy and cumbersome derivations.

Beamforming techniques have been an important approach to the design and optimization of the array pattern. Here the array elements are fed through a network that furnishes the phases and magnitudes necessary to obtain the desired radiation pattern. This approach offers the capability to employ various algorithms that are intended for the next generation ultra-wideband millimeter-wave phased array antennas. This book tries to augment this recent issue to the field of array synthesis.

In compliance with the development of massive MIMO and beamforming techniques in 5G technology, increasing the number of antenna elements has become an issue for further concern. The integrated antenna, which is composed of multiple antenna elements, can be a promising candidate for the next generation of technologies. The Smart Antenna Systems (SAS) and Massive MIMO systems are giving a strong and increasing impact relative to 5G wireless communication systems. They offer many benefits in terms of performance improvements with respect to omnidirectional antennas.

Therefore, this book aims to provide a good reference for practicing engineers as well as postgraduate students and researchers working in the field of antenna arrays. The book uses fundamental concepts that are necessary to explain the recent applications to provide a base on which the interested reader can either acquire new

knowledge about antenna array or furnish a platform for improving the existing antenna arrays for modern applications. The book can also serve as a useful tool for researchers (academia and industry) to draw inspiration for the design and development of array antennas for next-generation systems. This book is recommended for researchers and professionals in the field and may be used as a supplementary reference book on array antennas as it offers a concise guide for students and readers interested in studying arrays and their design optimization.

> **Jafar Ramadhan Mohammed** College of Electronic Engineering, Ninevah University, Mosul, Iraq

> **Khalil Hassan Sayidmarie** College of Electronic Engineering, Ninevah University,Mosul, Iraq

> > **1**

other side [17].

**Chapter 1**

Introductory Chapter:

Optimization

Introduction to Array Pattern

*Khalil H. Sayidmarie and Jafar Ramadhan Mohammed*

that aim to improve and optimize the radiation pattern of array antennas.

Array antennas offer versatile and flexible solutions to the requirement for desired radiation patterns. The total field of the array can be controlled by five array parameters that are the main design parameters [1]. These are: the geometrical layout of the array elements and their spacings, the excitation amplitude and phase of the individual elements, and finally the pattern of the individual elements. These factors have been utilized by many array synthesis techniques that use either analytical or numerical approaches. These techniques have been extensively studied and are well documented [2, 3]. This chapter aims at presenting recent techniques

While most of the array pattern synthesis approaches deal with all of the elements of the array antenna, the techniques presented in Chapter 2 offer easier solutions as only a limited number of the elements need to have their magnitudes and phases adjusted. Such approaches reduce the cost and complexity of the optimization process and achieve the desired radiation patterns by modifying the excitations of a small number of elements. Toward achieving this goal, earlier techniques that were based on simple analytical procedures have utilized only two or four elements at the side of the array to reduce the sidelobe level [4–9]. These simple analytical approaches have demonstrated the feasibility of the techniques in finding the proper excitations of the side elements. The same idea was developed to the case of planar arrays where much larger number of elements is used and much less number of controllable elements was required. Thus, it would be more economical if only the side elements are made controllable for the improvement of the array pattern [10]. The deployment of the side elements was also found applicable to improve the sum and difference patterns [11]. Some other effective methods based on either controlling the steer angle in a certain sub-array configuration or even sharing the element excitations at the tail of the array were also used to generate an improved sum and difference patterns in the tracking antenna arrays [12, 13]. The use of the side elements for obtaining a wide-angle null in the radiation pattern was presented in [14, 15]. Other approaches have utilized few elements at the center of the array to achieve better adaptive responses [16]. The side element idea was also deployed for the synthesis of asymmetrical radiation pattern where it is desirable to highly reduce the sidelobe on one side of the main beam while tolerating a higher sidelobes on the

While simple analytical approaches give better insight into the mechanism of the antenna pattern improvement, global numerical optimization methods have been proved to give better performance and optimum results [18–20] than those analytical approaches. In order to show the superiority and the power of the global optimization methods that were presented in [18–20] among the analytical approaches that were
