Sunday, July 28, 2013

Textbook Review: Antenna Engineering Handbook, Fourth Edition by John L. Volakis

As a PhD Candidate, I read multiple textbooks related to my research in antennas and antenna arrays. I've found a few textbooks that contain fundamental antenna theory that are written by authors people consider to be experts in the fields of electromagnetics and antennas. Today, I will write a review a textbook by John L. Volakis titled Antenna Engineering Handbook, Fourth Edition. See the picture below for the cover.

Front cover of Antenna Engineering Handbook, Fourth
Edition
by John L. Volakis
Before I review the book, you should be aware that this book has prerequisites that are required for you to understand the material that Volakis covers because it his material is directed at electrical / electronic engineers and graduate students interested in antenna design:

  1. You need a solid understanding of electromagnetics including Maxwell's equations.
  2. You need to know Calculus and differential equations.
  3. A basic understanding of physics would also help.

An interesting part about this book is that its 59 chapters are written by various authors including Volakis, Douglas H. Werner, Frank B. Gross, Leo C. Kempel, and Steven R. Best. In addition to writing two chapters, Volakis edited the text. In essence, the fourth edition of this text brought in multiple experts in various aspects of antenna design and theory together.

The chapters are organized into four parts:
  1. Introduction and Fundamentals
  2. Types and Design Methods
  3. Applications
  4. Topics Associated with Antennas
I will describe the four parts of the text book below with brief descriptions of sample chapters within those four parts. For the sake of space, it is not feasible for me to summarize all of the chapters in this book. The interested reader is welcome to check out a copy of this book from a local library and peruse chapters not summarized in this review.

Part 1: Introduction and Fundamentals

The first part of the text begins with a review of antenna fundamentals, arrays, and mobile communications. Volakis briefly describes topics important to antenna theory such as Huygens' and Equivalence Principles, antenna directivity, power transfer, and infinitesimal dipole antennas. If you want to learn about basic antenna theory in detail including derivations of electric and magnetic fields of the infinitesimal dipole antenna, you will find this text lacking.

The second chapter discusses frequency bands for communications. For the most part, this chapter can be skipped, as this topic is more or less regulatory. However, the author of this chapter gives nice tables that show frequency bands, so it is a good reference none the less.

The third and final chapter in Part 1 was writen by John N. Sahalos and gives a detailed overview of discrete antenna antenna array theory. The coverage is not as detailed as what Balanis discusses in his textbook (Antenna Theory: Analysis and Design, Third Edition). However, I understood the theory that Sahalos discussed including the array factor equation, uniform linear arrays, and Chevyshev arrays. Like Balanis, Sahalos assumes that the antenna elements are infinitesimal dipoles. This means that the theory discussed here does not include interelement coupling and detuning. Again, this is basic antenna theory, and more detailed discussions of antenna arrays are saved for later in the book.


Part 2: Types and Design Methods

This part of the book discusses various types of antenna designs. The antennas include dipoles, circular loops, small antennas, microstrip antennas, frequency independent antennas, horn antennas, and helical antennas. In essence, if you're looking to design a certain type of antenna, you will find it in one of the twenty chapters in this part. Whereas Part 1 gave a one chapter introduction on antenna array theory using the array factory equation, Part 2 includes three chapters on phased arrays, conformal arrays, and ultra wideband arrays. The chapter on phased arrays gives a more detailed discussion on accounting for mutual coupling between elements, and it discussing designing phased array feeds as means of connecting the antenna elements to a common source (i.e. transmitter or receiver).

A nice aspect of this part is that you do not need to read all twenty chapters of this part, nor do you need to read them in consecutive order to understand theory covered in a later chapter. One should note that the dipole antenna chapter focuses on practical dipole antenna designs including folded dipoles, sleeve dipoles, and monopole antennas. As such, the chapter lacks detailed derivations of the equations used to design such antennas, and the author refers the interested reader to other published literature. For the reader interested in understanding how the electric magnetic fields for a dipole antenna are derived, I highly recommend Balanis' Antenna Theory textbook.

As noted, Part 2 of this text also chapters covering frequency independent (i.e., wideband) antennas. Chapter 13 discusses frequency independent antennas in detail starting with a mathematical explanation of how an antenna can be designed to obtain gain and impedance that are independent of frequency. This chapter also discusses several kinds of spiral antennas, log-periodic antennas, and sinuous antennas.


Part 3: Applications

Having covered fundamentals and various antenna designs, the text now turns to how these antennas can be used in the real world as well as more complex antennas such as fractal antennas. I would say that this part of the text is a mixture of theory and practical applications. The practical chapters include the ones on mobile handset antennas, antennas designed for particular frequency bands such as UHF, and automobile antennas. Below is a partial list of the chapters contained within this section:
  • Chapter 32: Active Antennas
  • Chapter 33: Fractal Antennas
  • Chapter 36: Mobile Handset Antennas
  • Chapter 37: Broadband Planar Antennas for High-Speed Wireless Communications
  • Chapter 42: Antenna Tracking
  • Chapter 46: Seeker Antennas
  • Chapter 47: Direction Finding Antennas
I will discuss Chapters 32 and 33 only to limit this post's lengths. To start, the topics covered in Chapter 32 include antennas integrated with RF amplifiers and rectennas. The term "rectenna" is an amalgamation of the words "rectifying antennas."In its simplest form, a rectenna consists of the antenna, a rectifying device such as a diode, and a low-pass filter. The general idea is to convert high-frequency RF energy into DC voltage and current when attached to a load. One would use a rectenna as an energy harvesting device, as is the case with passive RFID tags. The author explains the mathematical concepts behind rectennas and gives design examples of both narrowband and broadband rectenna design.

In addition, I found Chapter 33 (Fractal Antennas) very interesting. The authors explain how wideband antennas can be synthesised using fractals. They also describe wideband fractal antenna arrays with theory on how infitesimal dipoles can be layed out in a semi-random fashion using polyfractals. They note that an issue with uniform linear arrays is that wideband operation is not possible because the periodic nature of the array causes grating lobes (i.e., undesired sidelobes with same directivity as the main lobe) to appear at higher frequencies of operations. The antenna elements also interact with each other causing them to detune and have poor impedance matches. Hence, the idea is to layout the elements in a semi-random fashion such that the elements are not uniformly spaced throughout the length of the array. The authors also give examples of planar arrays based on fractal and aperiodic tilings. Like the linear areas, the idea is to make sure that elements are not uniformly spaced when layed out in a plane. This also prevents grating lobes, and it antenna elements from detuning each other at higher frequencies.

Part 4: Topics Associated with Antennas


This part of the text does not discuss antenna theory and design per se. Instead, the various authors discuss different topics that are important corequisites for antenna designs. For example, Chapter 51 discusses transmission lines, and Chapter 52 discusses impedance matching techniques. If the reader, like myself, has a detailed background in electromagnetics and RF/Microwave engineering, these two chapters will serve as a review. There are plenty of textbooks devoted separately to transmission lines (including waveguides) and impedance matching. However, it is good that Volakis chose to include these chapters, as they provide useful information for engineers or graduate students who do not have sufficient knowledge in those topics. After all, a good antenna design is useless if it is not properly connected to the rest of the communication system.

Regarding communication systems, Volakis also included chapters on propagation models, multipath techniques, frequency selective surfaces (FSS), radomes, materials design data, and computational electromagnetics. Again, there exists many books on each of those topics. However, it is convenient that they are included with the text for those wishing to get a brief introduction or review of said topics. 


Conclusion

Volakis' fourth addition of his Antenna Engineering Handbook is a great textbook to read and keep in your antenna engineering / design reference collection. Volakis gives a brief review of antenna fundamentals, but the reader needs to have an understanding of electromagnetics (including Maxwell's Equations) because Volakis assumes that the reader understands that topic a priori. The book focuses on many types of antenna designs with plenty of examples and design graphs. I gave a summaries of a few of the chapters in this review. Finally, the fourth part of the textbook is optional reading because it contains chapters that are corequisites for antenna designs. The reader does not need to read these chapters in order to understand antenna design and theory. However, these chapters are useful reads nonetheless to understand how to integrate different antenna designs into wireless communication systems.