Waveguides are electronic devices that are used to guide or confine a wave. The wave may be electromagnetic, light, a radio frequency, a digital signal, audio, dielectric or radar. Waveguides can be designed to carry waves over a large section of the electromagnetic spectrum, but they are especially helpful in the microwave and optical frequency ranges. Depending on the frequency, waveguides can be made from either conductive or dielectric materials. Waveguides are used for transferring both power and communication signals. Like most other types of electrical devices, there are numerous types of waveguides available.
RF or micro waveguides consist of hollow metal tubes that have a cross-section that is circular, elliptic or rectangular. They may even be filled with dielectric material in solid or gaseous states. Hollow waveguides must be one half wave length or more in diameter for them to support one or more transverse wave modes. In some waveguides there may be a positive pressure inside of it which enables it to detect any of potentially dangerous RF leaks. Another way to detect any RF leakage of a waveguide is to position a vacuum inside of it. Any leaks can then be detected in basically the same way.
An example of a dielectric waveguide is an optical fiber. Optical waveguides use optical fiber cables. These cables are filled with a dielectric, solid material and used as a transmission line. A dielectric waveguide consists of a dielectric material that is surrounded by another dielectric material, such as air, glass, or plastic, with a lower refractive index. However, a metallic waveguide that is filled with a dielectric material is not a dielectric waveguide.
In RF applications, antennas are used as waveguides and they emit the radio frequencies through the slots. Parabolic reflector antennas are also sometimes used. A closed waveguide is used for electromagnetic applications. It is made of a hollow or dielectric filled tube and the walls are electrically conductive. Slotted waveguides are usually used for radar and other similar applications. The structure of the waveguide is designed to confine and support the energy of an electromagnetic wave to a specific relatively narrow and controllable path.
While selecting a waveguide, you need to consider the waveguide propagation mode, polarization, operating wavelength and the guide shape and size.