The ridge waveguide, which is a rectangular waveguide with one or more metal inserts (ridges), is an important transmission line in microwave engineering, now widely used in commercial electronics and communications devices. This book collects together much of the work of Professor Helszajn, an international authority in the field, and will enable the reader to have direct access to this important work without need for exhaustive search of research papers. Generously illustrated, it is likely to become the definitive reference source on this topic.