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# Waveguide Internal Surface Roughness

## Waveguide Internal Surface Roughness

(OP)
Hi there!
If anyone can clarify the relationship between propagation frequency and internal roughness level of a circular waveguide please?
Regards
Replies continue below

### RE: Waveguide Internal Surface Roughness

From first principles, these are presumably all in linear proportion:
• Wavelength (inverse of frequency)
• Size of waveguide (closest appropriate standard size)
• Roughness requirements
There are probably some factors impacting loss that would not scale in linear proportion.

A Google search of the obvious search terms shows some scholarly articles on the subject.

### RE: Waveguide Internal Surface Roughness

Frequency sets your skin depth (e.g., 0.66 microns @ 10GHz), right? So the roughness of your surface can/will have a major effect on how far the signal of interest travels (for a rough surface and a small skin depth, it has to travel over every peak/valley in the surface). Pretty easy to ignore at 1GHz, but difficult to ignore at 100GHz.

Dan - Owner
http://www.Hi-TecDesigns.com

### RE: Waveguide Internal Surface Roughness

(OP)
Thanks MacGyverS2000. Yes frequency sets the skin depth. Please say what percent of surface roughness be of skin depth not to effect the propagation or say a single digit percentage of loss?

### RE: Waveguide Internal Surface Roughness

Depends on the length of the wave guide doesn't it? All the waveguide I've seen is extruded and very smooth, but it was for only a few feet.

### RE: Waveguide Internal Surface Roughness

For high-efficiency guides, they'll silver coat the inside since it has a slightly lower resistivity.

Dan - Owner
http://www.Hi-TecDesigns.com

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