It is a great pleasure to have a chance to thank the three most important people in my academic life. I would like to thank Professor Zhengde Wu, who was my supervisor when I studied at the University of Electronic Science and Technology of China as a master’s student. Professor Wu equipped me with the most essential engineering skills which have benefited me ever since. I would also like to thank Professor Zhenghe Feng and Professor Magdy F. Iskander. Professor Feng was my advisor when I studied for my PhD degree at Tsinghua University. Professor Iskander was my supervisor when I worked as a postdoctoral graduate at the University of Utah. Both of them are my lifetime mentors. With their care and encouragement, I successfully made a mid‐life career change, from an engineer to a professor. Since I joined Tsinghua University, I have cooperated successfully with Professor Feng and Professor Iskander, and I cannot thank them enough for all their help and guidance during this period, and hope to enjoy a continuous fruitful collaboration with them.

To the companies and individuals who provided illustrations and the copyright permissions for the illustrations, I am most appreciative. I am especially grateful to Yaobin (Richard) Gu and Xiaodong (Amanda) Jiang from Shanghai Amphenol Airwave Inc., who provided most of the photos and drawings of the production antennas in the book. I would also like to express my gratitude to the staff at John Wiley & Sons, especially James Murphy, Renee Lee, and Shelley Chow.

In the second edition of the book, some practical designs of real phones are included. I would like to thank Xiaohui Pi and Dr. Wendong Liu from Xiaomi Inc. for providing phone samples. I would also like to thank Lizhong Li from Shanghai Amphenol Airwave Inc. for providing semifinished antenna parts specially prepared for the book.