What are, how do they work and for what serve the waveguides? It is this post’s subject. The mathematics of waveguides is too complex and won’t be explained in this post.
What are?
Waveguides are a mean to transport electromagnetic waves in frequency of gigahertz (GHz), the frequency band of microwaves, from a point to another. Is made of a hollow conductor material with a dielectical material inside, usually air. The goal is to transport high power electromagnetic waves with minimum irradiation loss, because the wave propagation is limited by conductor material.
Inside this component, the electromagnetic wave spreads with reflections in the inner walls, similar to optic fiber. Can only transmit waves in a frequency band.
Propagation transversal modes
A electromagnetic wave in the air can spread in TEM (Transversal Electromagnetic) mode, in this mode, the electric and magnetic field are perpendicular to wave propagation direction. Inside a waveguide, can spread in Transversal Magnetic (TM) mode, Transversal Electric (TE) mode or hybrid mode (HE). In the TM, only the magnetic field is perpendicular to propagation direction. While in TE, only the electric field is perpendicular to propagation direction vector.
In HE mode, neither the electric field nor the magnetic field are perpendicular to wave propagation direction. Every vector has three components, each one in x, y and z axis, usually considerate the wave propagation direction in the z axis.
- In TE, the z component of electrical field (E_{z}) is equal to zero;
- In TM mode, the z component of magnetic field (H_{z}) is equal to zero;
- In TEM mode, E_{z}=H_{z}=0;
- In HE, E_{z}=H_{z}≠0.
Types of waveguides
The most common type is the rectangular waveguide.
In the rectangular guide, the wave can’t spread in TEM mode, only in TE or TM. Below is showed how an electromagnetic wave spread in both modes.
This is a circular waveguide. In this type, only TE and TM are spread, are used cylindrical coordinates and Bessel functions to calculate the field components inside the guide. Waves are propagated in a different mode and it is less common than the rectangular waveguide.
Exist flexible waveguides, are used in situations where flexibility is necessary, like connect the antenna to transceiver when you can’t make a direct connection. In flexible guides, internal walls are corrugated to facilitate the flexion.
Elliptical waveguides are also flexible.
Exist various other types of waveguides, but these are the most known.
Some applications
Waveguides are used in microwave ovens to direct the microwaves to the food. Click in the button below to know how this household appliance works.
Are used in devices to high frequency circuits to telecommunications, like couplers, attenuators, isolators, filters, switches, etc.
I like how you mentioned that waveguides transport electromagnetic waves. Last week my husband was telling me about them and I honestly had no idea what they were and what they do. I appreciate you helping me learn more about what waveguides are and what they do!
You’re welcome.