Waveguide basics tutorial

- overview, summary, tutorial about the basics of what is a waveguide and the basic waveguide theory.

Waveguide tutorial includes:

    •  Waveguide basics
    •  Waveguide theory
    •  Waveguide impedance
    •  Flexible waveguide
    •  Waveguide couplers and transitions
    •  Waveguide dimensions and sizes
    •  Waveguide flanges
    •  Waveguide junctions
    •  Waveguide directional coupler
    •  Waveguide bends

RF waveguides are a form of RF feeder used for microwave applications. For use, the basics of waveguide technology are easy to comprehend, although the mathematics involved can become complicated when wave theory and the like are used. Waveguides are a guide for electromagnetic waves and this gives rise to the name waveguide.

Waveguides effectively confirm and direct a wave within a given boundary. Within many electronic circles, waveguides are most commonly used for microwave RF signals, the same principles can be used for many forms of wave from sound to light.

RF waveguide basics

Waveguides are used in a variety of applications to carry radio frequency energy from one pint to another. In their broadest terms a waveguide is described as a system of material that is designed to confine electromagnetic waves in a direction defined by its physical boundaries. This definition gives a very broad view of waveguides, but indicates that waveguide theory can be applied in a number of areas and in a variety of different ways.

Electromagnetic waves propagating in open space travel out in all directions and can be thought of as spherical waves travelling out from a central source. As a result the power intensity decreases as the distance increases - it is proportional to the power of the source divided by the square of the distance. The waveguide operates by confining the electromagnetic wave so that it does not spread out and losses resulting from this effect are eliminated.

Typically a waveguide is thought if as a transmission line comprising a hollow conducting tube, which may be rectangular or circular within which electromagnetic waves are propagated. Unlike coaxial cable, there is no centre conductor within the waveguide. Signals propagate within the confines of the metallic walls that act as boundaries. The signal is confined by total internal reflection from the walls of the waveguide.

Waveguides will only carry or propagate signals above a certain frequency, known as the cut-off frequency. Below this the waveguide is not able to carry the signals. The cut-off frequency of the waveguide depends upon its dimensions. In view of the mechanical constraints this means that waveguides are only used for microwave frequencies. Although it is theoretically possible to build waveguides for lower frequencies the size would not make them viable to contain within normal dimensions and their cost would be prohibitive.

As a very rough guide to the dimensions required for a waveguide, the width of a waveguide needs to be of the same order of magnitude as the wavelength of the signal being carried. As a result, there is a number of standard sizes used for waveguides as detailed in another page of this tutorial. Also other forms of waveguide may be specifically designed to operate on a given band of frequencies

Types of RF waveguide

There is a number of different types of RF waveguide that can be used, bought and designed.

Typically waveguides are thought of as being rectangular in cross section as this is the most common form of waveguide. However other types and approaches may be used.

• Rectangular waveguide:   This is the most commonly used form of waveguide and has a rectangular cross section.
• Circular waveguide:   Circular waveguide is less common than rectangular waveguide. They have many similarities in their basic approach, although signals often use a different mode of propagation.
• Circuit board stripline:   This form of waveguide is used on printed circuit boards as a transmission line for microwave signals. It typically consists of a line of a given thickness above an earth plane. Its thickness defines the impedance.

In addition to these basic forms, there are also flexible waveguides. These are most widely seen in the rectangular format. Flexible waveguide is often used to connect to antennas, etc that may not be fixed or may be moveable.

Waveguides are more expensive than other forms of RF feeder. However waveguides offer a number of advantages that mean they are the only feasible solution in many applications. Although waveguide is not nearly as widely used as other forms of feeder such as coax, it still forms and essential method of transferring RF power, especially are microwave frequencies.

. . . .   |   Next >>