This book is designed for both the scientific audience, research and development engineers and university students. The fundamentals of radio frequency antenna beam forming are explained in this book. The principles of beam focusing and beam steering in near field and far field are visualized with 2D and 3D simulations and compared with measurement results. Besides linear and planar antenna arrays, also conformal arrays, i.e. concave and convex antenna arrays, suitable for certain applications, are investigated and presented. Also related applications of open loop and closed loop beam forming, and massive MIMO, which is one of the break-through technologies for 5G and future 6G and involves an extremely large number of antenna elements for the multi-user beam forming, are discussed in detail. Also covered are large scale antenna arrays as well as thinned antenna arrays with electrically large distances between the antenna elements.