WAVEGUIDE THEORY AND APPLICATION

LEARNING OBJECTIVES

Upon completion of this chapter the student will be able to:

• Describe the development of the various types of waveguides in terms of their advantages and disadvantages.
• Describe the physical dimensions of the various types of waveguides and explain the effects of those dimensions on power and frequency.
• Explain the propagation of energy in waveguides in terms of electromagnetic field theory.
• Identify the modes of operation in waveguides.
• Explain the basic input/output methods used in waveguides.
• Describe the basic principles of waveguide plumbing.
• Explain the reasons for and the methods of terminating waveguides.
• Explain the basic theory of operation and applications of directional couplers.
• Describe the basic theory of operation, construction, and applications of cavity resonators.
• Describe the basic theory of operation of waveguide junctions.
• Explain the operation of ferrite devices in terms of their applications.

INTRODUCTION TO WAVEGUIDE THEORY AND APPLICATION

That portion of the electromagnetic spectrum which falls between 1000 megahertz and 100,000 megahertz is referred to as the MICROWAVE region. Before discussing the principles and applications of microwave frequencies, the meaning of the term microwave as it is used in this module must be established. On the surface, the definition of a microwave would appear to be simple because, in electronics, the prefix "micro" normally means a millionth part of a unit. Micro also means small, which is a relative term, and it is used in that sense in this module. Microwave is a term loosely applied to identify electromagnetic waves above 1000 megahertz in frequency because of the short physical wavelengths of these frequencies. Short wavelength energy offers distinct advantages in many applications. For instance, excellent directivity can be obtained using relatively small antennas and low-power transmitters. These features are ideal for use in both military and civilian radar and communication applications. Small antennas and other small components are made possible by microwave frequency applications. This is an important consideration in shipboard equipment planning where space and weight are major problems. Microwave frequency usage is especially important in the design of shipboard radar because it makes possible the detection of smaller targets.

Microwave frequencies present special problems in transmission, generation, and circuit design that are not encountered at lower frequencies. Conventional circuit theory is based on voltages and currents while microwave theory is based on electromagnetic fields. The concept of electromagnetic field interaction is not entirely new, since electromagnetic fields form the basis of all antenna theory. However, many students of electronics find electromagnetic field theory very difficult to visualize and understand. This module will present the principles of microwave theory in the simplest terms possible but many of the concepts are still somewhat difficult to thoroughly understand. Therefore, you must realize that this module will require very careful study for you to properly understand microwave theory. Antenna fundamentals were covered in NEETS, Module 10, Introduction to Wave Propagation, Transmission Lines, and Antennas.

This module will show you the solutions to problems encountered at microwave frequencies, beginning with the transmission of microwave energy and continuing through to waveguides in chapter 1. Later chapters will cover the theory of operation of microwave components, circuits, and antennas. The application of these concepts will be discussed more thoroughly in later NEETS modules on radar and communications.

Q.1 What is the region of the frequency spectrum from 1000 MHz to 100,000 MHz called?
Q.2 Microwave theory is based upon what concept?