EM Waveguide Modes: What are they and how are they used

In summary, in EM waveguides, there are various modes that represent specific, discrete solutions to the Hemholtz equation. These modes only allow specific frequencies to propagate, with the cutoff frequency being the limit for propagation. The choice of mode in a waveguide is typically determined by the desired size and power transfer capabilities. The lowest mode is often preferred, as it allows for larger waveguides and maximum power transfer. Modes with frequencies below the cutoff frequency do not propagate due to their wavelengths being too long for the waveguide. A general explanation of modes and their physical meaning and relevance can be found in sources such as Wikipedia and Microwaves101.
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bladesong
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Title pretty much says it all. In EM waveguides (rectangular, circular, what have you), I understand there are various "modes." I'm gathering that these represent specific, discrete solutions to the Hemholtz equation, and therefore there are only specific frequencies that will propagate?

What happens between these frequencies?

What determines which mode you would use in a waveguide and why?

Finally, the cutoff frequency - modes with frequencies BELOW this number are the ones that don't propagate, correct (i.e. a HPF vs an LPF)?

Thank you in advance - additionally, any general explanation of modes and their physical meaning and relevance would be greatly appreciated. My material seems to just jump right into how to determine these without bothering to explain what they are, where they come from or how they're used.
 
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Anyone?
 
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Imagine waveguides as oscilators, resonance circuits or antennas. You can force any frequency on them but only those with the correct wavelengths will resonate ("fit into the waveguide"). For the rest of frequencies the impedance will be high to the point of being infinite for some frequencies.
bladesong said:
What determines which mode you would use in a waveguide and why?

Don't people almost always choose the lowest mode because the resulting waveguide is the largest (i.e. easy to manufacture with given precision)? I may also recall something about maximum power transferred in the lowest modes as opposed to the higher modes but I can't guarantee that. That may be important for radars, transmission antennas, etc.
bladesong said:
Finally, the cutoff frequency - modes with frequencies BELOW this number are the ones that don't propagate, correct (i.e. a HPF vs an LPF)?

Their wavelengths (actually half of the wavelength) are too "long" to fit in the waveguide.

bladesong said:
Thank you in advance - additionally, any general explanation of modes and their physical meaning and relevance would be greatly appreciated.

Hopefully, I didn't mess up too much. It's been over a decade since the last time I dealt with waveguides.Sources:
Wikipedia: Transverse mode
Microwaves101: http://www.microwaves101.com/encyclopedia/TEM.cfm
 
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1. What are EM waveguide modes?

EM waveguide modes are electromagnetic waves that travel through a hollow metallic or dielectric structure, known as a waveguide, instead of through free space. These modes are used to transmit and manipulate electromagnetic signals, particularly at high frequencies.

2. How are EM waveguide modes generated?

EM waveguide modes can be generated by applying a suitable electromagnetic field at one end of the waveguide. This field excites the electrons in the waveguide, causing them to oscillate and produce the desired mode. Alternatively, modes can also be generated by introducing a source of electromagnetic radiation into the waveguide.

3. What are the types of EM waveguide modes?

The two main types of EM waveguide modes are transverse electromagnetic (TEM) modes and transverse electric/magnetic (TE/TM) modes. TEM modes have both the electric and magnetic fields perpendicular to the direction of propagation, while TE/TM modes have either the electric or magnetic field perpendicular to the direction of propagation.

4. How are EM waveguide modes used in practical applications?

EM waveguide modes are widely used in various applications such as microwave communication, radar systems, and particle accelerators. They are also used in microwave ovens, where the food is heated by the absorption of the electromagnetic energy carried by the modes.

5. What factors affect the propagation of EM waveguide modes?

The propagation of EM waveguide modes can be affected by various factors such as the geometry and dimensions of the waveguide, the material properties of the waveguide, and the frequency of the electromagnetic field. The presence of conductive or dielectric materials near the waveguide can also affect the propagation of modes.

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