The Waveguide was invented by George C Southworth. To honor his work in Wave-guide, he was bestowed with the Morris N. His contributions to the field of Radio Physics were commendable. Waveguides are used to direct and propagate Electromagnetic waves from one point to another. They are generally used to transmit high frequency waves such as Microwaves, Radio waves, Infrared waves etc. For low frequency waves which are less than 1 MHz, parallel transmission lines or co-axial cables are used.
Wave-guide is represented by its dispersion characteristics that has a certain cut-off frequency. The signals having frequencies above this cut-off frequency are allowed to propagate through the Wave-guide and the signals having frequencies below this frequency will face a high reflection. A Waveguide acts like a high pass filter due to this characteristics. The dispersion characteristics can be altered by loading the Wave-guide with metal or di-electric medium.
The most common type of Waveguide is a hollow conductive metal pipe which carries high frequency Radio Waves. They also exist in the form of wires, coaxial cables, parallel plates, or optical fibers. Metal Waveguides consists of an enclosed conducting metal pipe and the wave guiding principle works on the total internal reflection from the conducting walls. They are of two types:. Dielectric Waveguides consists of dielectrics and the reflection from dielectric interfaces helps in the propagation of electromagnetic waves along the Waveguide.
The two types of Wave-guide Modes that is necessary for propagation of Electromagnetic waves in the Waveguides are:. Waveguide is defined as a geometrical structure which propagates electromagnetic energy in a preferred direction in space from one point to another within a certain frequency range.
They do not operate under transverse electromagnetic modes TEM as they are built with single conductor. The propagation of a wave in a Wave-guide TE or TM waves has very different characteristics than the propagation of a wave on a transmission line TEM waves. This is because when a wave is transmitted at one end of the Wave-guide, it gets reflected from the sides of the Wave-guide.
A: Strictly speaking, yes. A rubber hose is a waveguide for flowing water and the energy it transfers. There are also waveguides which do the same for audio energy, such as the Bose Wave Radio. PC board microstrip and stripline structures are also EM-energy waveguides.
For EM energy, there are two types of waveguides: the coaxial cable and the older, classic waveguide which is still in use. A: Yes, it has a solid center conductor surrounded fully by an enveloping shield.
Together, they function to support the propagation of RF energy while confining it to the desired path. But when RF engineers use the term waveguides, they generally do not mean coaxial cable, as a coaxial cable is more like a transmission line. A: The classic waveguide is a metal tube, usually with a rectangular cross-section, which can range in length from a few centimeters to many meters Figure 1.
While waveguides are usually conductive metal enclosures, it is possible to build waveguides using dielectric surfaces to confine the RF wave energy, but they are rarely used now for various reasons. They often did the basic sheet-metal work of cutting and soldering the needed waveguides, as standard ones did not exist or would take time to order, fabricate, and deliver! Q: Why do you even need a waveguide when you have convenient coaxial cable which can carry RF?
However, they have increasing power losses as frequency increases. Also, as frequencies increase, the coaxial cables get thinner some are just a few millimeters in diameter and so their power-handling capability also is reduced due to possible flashover between the center conductor and outer shield. Further, self-heating of coaxial cables due to inherent, unavoidable losses affects the consistency of their performance and degrades many of their key specifications.
It has a sinusoidal shape in cross-section. By the electric field also arises a magnetic field. However, the magnetic field cannot stand vertically on a metallic conductor. As propagation direction remains only the direction which is passed through the waveguide.
The electric field changes over time with the frequency, and has in the longitudinal direction of the waveguide maxima and minima in the distance of half the wavelength. High frequency energy that is fed into a waveguide, generates an electromagnetic transverse wave TEM mode whose electric and magnetic fields are perpendicular to each other. The electric field is established between the two wider waveguide walls, the magnetic field lies between the two narrower walls.
These fields do not remain in the respective states. Considered over the timeline, they change the intensity and polarity in the rhythm of the input signal. This electromagnetic wave propagates in the waveguide at near-light speed. The electric and the magnetic field change its strength and polarity permanently, but they are always perpendicular to each other locally.
If the electric field is in propagation direction, it is called an E-wave or TM wave T ransverse M agnetic. If the magnetic field is in propagation direction, it is called an H-wave or TE wave T ransverse E lectric.
The wave propagation in the waveguide can be partly explained with the help of geometrical optics. The properties of the waves in a waveguide can be derived from those of a plane wave in free space. The electric field E is perpendicular to the plane of representation here and can therefore only be marked in different colors.
The green color symbolizes the zero line. The angle of incidence is equal to the angle of reflection. During the reflection at the wall, the wave undergoes a phase shift of degrees. The superposition of the two waves can be seen in the image because the formation of local minima and maxima as much red or blue colored areas at a certain distance from the metal wall.
At a distance of. The positive wavefront of the incident wave colored in red coincides with the negative wave front of the reflected wave colored in blue. Here in the image this results in magenta by the additive color mixing.
Energetically correct these areas should be green. The picture moves permanently to the right with the arrival of the incident wave. The process of reflection is repeated at this second wall, replacing the permanent exposure of the incident wave. Positive and negative maxima of the wave arise between these two walls as before only at one wall.
It is also imaginable from this graph that optimum wave propagation in the waveguide is only possible at an optimum angle of incidence of the incident wave. Practically, in the waveguide arise voltage minima and maxima by multiple interference of reflected on the walls energy parts. This distance corresponds. Unfortunately, this angle is difficult to measure.
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