Realization of Slow Wave Phenomena Using Coupled Transmission Lines and Their Application to Antennas and Vacuum Electronics
Md. R. Zuboraj and John L. Volakis
Over the past decade, slow waves, backward traveling waves, and other exotic propagation phenomena has been extensively used to modify and control the radiation and coupling properties of microwave and RF devices. Example applications include the development of miniature antennas, microwave filers and couplers, traveling wave tubes (TWTs), and backward wave oscillators. Typically, designs are carried out using a variety of computational tools, but with limited reference to the dispersion diagrams that control the radiation and propagation properties of these devices. For the first time,
Broadband Metamaterials in Electromagnetics: Technology and Applications Edited by Douglas H. Werner
Copyright © 2017 Pan Stanford Publishing Pte. Ltd.
ISBN 978-981-4745-68-0 (Hardcover), 978-1-315-36443-8 (eBook) www.panstanford.com in this chapter, we endeavor to provide an understanding of how exotic propagation phenomena can be explained and controlled using dispersion engineering. More importantly, these novel propagation modes are generated using a set of coupled transmission lines that can be printed on simple substrates. By controlling the propagation constant on each line, as well as their mutual capacitance and inductance, it is shown that dispersion diagrams of second, third, and fourth order can be realized. In turn, this leads to transmission lines that support various exotic modes. These modes are subsequently used to (i) improve the electronic efficiency of TWTs, (ii) miniaturize antennas, reaching their optimal limits, (iii) increase antenna directivity, and (iv) control antenna bandwidth. Examples of the latter are provided.