tailieunhanh - Fundamentals of Engineering Electromagnetics - Chapter 7

Bất kỳ cấu trúc vận chuyển sóng điện từ có thể được coi là một ống dẫn sóng. Thông thường, tuy nhiên, thuật ngữ này dùng để chỉ một trong hai cấu trúc kim loại hoặc điện môi vận chuyển năng lượng điện mà không có sự hiện diện của một con đường mạch hoàn chỉnh. Ống dẫn sóng bao gồm dây dẫn và các chất điện môi (bao gồm cả không khí hoặc chân không) được gọi là ống dẫn sóng kim loại. Ống dẫn sóng bao gồm các vật liệu điện môi chỉ được gọi là ống dẫn. | 7 Waveguides and Resonators Kenneth R. Demarest The University of Kansas Lawrence Kansas . INTRODUCTION Any structure that transports electromagnetic waves can be considered as a waveguide. Most often however this term refers to either metal or dielectric structures that transport electromagnetic energy without the presence of a complete circuit path. Waveguides that consist of conductors and dielectrics including air or vacuum are called metal waveguides. Waveguides that consist of only dielectric materials are called dielectric waveguides. Metal waveguides use the reflective properties of conductors to contain and direct electromagnetic waves. In most cases they consist of a long metal cylinder filled with a homogeneous dielectric. More complicated waveguides can also contain multiple dielectrics and conductors. The conducting cylinders usually have rectangular or circular cross sections but other shapes can also be used for specialized applications. Metal waveguides provide relatively low loss transport over a wide range of frequencies from RF through millimeter wave frequencies. Dielectric waveguides guide electromagnetic waves by using the reflections that occur at interfaces between dissimilar dielectric materials. They can be constructed for use at microwave frequencies but are most commonly used at optical frequencies where they can offer extremely low loss propagation. The most common dielectric waveguides are optical fibers which are discussed elsewhere in this handbook Chapter 14 Optical Communications . Resonators are either metal or dielectric enclosures that exhibit sharp resonances at frequencies that can be controlled by choosing the size and material construction of the resonator. They are electromagnetic analogs of lumped resonant circuits and are typically used at microwave frequencies and above. Resonators can be constructed using a large variety of shaped enclosures but simple shapes are usually chosen so that their resonant frequencies can