Preface

A rectangular waveguide (RWG) is the best technology to guide high-frequency signals in traditional high-performance communication systems. As is well known, it is characterized by low losses, high power handling capacity and mechanical robustness. Its main drawbacks are size, weight and cost, which invalidate its use in new and emerging communication systems, such as constellations of low-cost and low-Earth-orbit satellites.

The most popular alternative to RWG is usually printed circuit technology, such as microstrip or coplanar lines. Despite the benefits of reduced cost, volume and ease of manufacture, these technologies present high power losses.

Since 2001, new planar and substrate-integrated waveguides have been developed that approach the desirable performance of an RWG, but are synthesized on one or more printed circuit boards. The first was the substrate-integrated waveguide (SIW), which emulates a dielectric-filled RWG in a single circuit board where the side walls are made of metallic via holes. Although SIW is a good alternative to classic planar technologies, the presence of lossy dielectric makes it impossible to achieve performance similar to that of the RWG. In 2014, the empty substrate-integrated waveguide (ESIW) was introduced as a composite of three soldered metalized circuit board layers where the middle layer had been emptied to emulate an RWG. ESIW is now the best approach to an RWG in terms of performance, but retains the characteristics of planar circuits: ease, compactness, mass production, low volume, low weight and low cost. Among other alternatives are the air-filled substrate-integrated waveguide (AFSIW), which is the practical implementation of the modified substrate-integrated waveguide (MSIW); the hollow substrate-integrated waveguide (HSIW), similar to AFSIW but implemented in low-temperature cofired ceramic (LTCC) technology; and the partially dielectric-filled empty substrate-integrated waveguide (PFESIW), which is an ESIW loaded with a longitudinal dielectric slab. Newer hybrid planar–3D waveguiding structures have arisen, implementing waveguides of either a single conductor (no TEM mode) or two conductors (pure TEM mode).

These novel hybrid technologies are receiving much research attention. Among the studies that have been published are several devices, advances in topology variations and in the manufacturing process, and newer techniques combining traditional planar processes with metal and plastic 3D printing. The maturity of these technologies and their use by the communications industry may increase the performance of communication devices, which in turn will have a major economic impact on the high-frequency communication sector.

The goals of this book are to present the basis of these new hybrid structures and to introduce advances in the design of devices and systems, manufacturing processes and tests, as well as the various applications where these technologies can be used.

The academic editorial board of this book wishes to thank all the colleagues whose contributions have made this project possible.
