Waveguides

Waveguides

A waveguide is a device used primarily in the conduction and transmission of microwaves. It is a hollow tube or pipe that takes the place of wire or coaxial cable to transmit a microwave signal a certain, usually short, distance. Because of the nature of microwaves, an efficient waveguide can carry more than 100,000 transmissions simultaneously.

It did not take scientists long to realize that simple cables were excellent for transmitting radio signals, but were inefficient in the transmission of high frequency signals. They had experimented with several tube-design conductors, finding that they, too, were impractical--unless the frequency of the signal was very high, much higher than any radio waves. As their knowledge of microwaves increased, scientists realized that pipe-design conductors were ideal for microwave transmission.

A waveguide can actually be a dielectric rod as well as a tube conduit, but the latter is used more frequently. Usually made from drawn brass, the waveguide is constructed in small circular or rectangular segments that are later assembled into a long pipe. The inside of the pipe, along which the signal travels, is plated with cadmium or nickel, although some special applications demand that the inside be made of gold or silver. As a microwave signal is sent through the pipe it bounces along the inside walls, taking the path described by the waveguide. If a waveguide is constructed properly, little loss of signal will occur throughout the pipe's "run."

Though it somewhat resembles a water pipe, the waveguide cannot conduct microwave signals around sharp curves or corners, so the run must be fairly straight. Also, waveguides lose efficiency over long distances, and many are restricted to less than 10 ft (3 m).

Almost every microwave application uses some kind of waveguide to conduct the signal from one place to another. The most common application is in a microwave oven, where a waveguide is used to direct the heating waves toward the cooking compartment. Microwave antennas use waveguides to carry microwaves to transmitting arrays and to collect them from receiving arrays. They are also used in radio telescopes, mass spectrometry, radio surveying, and burglar alarms.

The most recent evolution of the waveguide is a tube of light-carrying material called fiber optic cable. Utilizing the principle of total internal reflection, fiber optic cable bounces a beam of light over a long distance while retaining most of its original intensity. Fiber optics have formed the foundation of many new communication and information storage systems, particularly those that rely upon digital coding.