Waveguide Cutoff Freq & Attenuation

This worksheet calculates the frequency of rectangular waveguide below which attenuation increase precipitously, or the waveguide "cutoff" frequency (Fco). It also calculates the attenuation in the TE10 mode for said waveguide at a frequency entered by the user. Formulae and sanity checks were provided by Tom WA1MBA.

Initial values for WR90 waveguide at 10368 MHz are inserted. To run other examples, simply change the dimensions, frequency and units as desired and click on "Compute". Clicking the Reset button once will reset the input to the intitial conditions, and clicking it a second time will force a computation of those values to the output.

NOTE1:  At higher frequencies, such as at 20 GHz and above, the surface roughness becomes an appreciable fraction (in many cases greater than) a few skin depths. The exact process of surface treatment (plating, polishing) is a specialty of waveguide manufacturers who provide the highest quality waveguide for frequencies above 20 GHz. The roughness causes loss to rise. Some very high quality waveguide can be measured with loss as much as twice the calculated value.

NOTE2:  The calculations are imperfect from just below Fco to about 0.5% below Fco. To help you avoid this anomaly, the frequency "0.5% below Fco" is shown.

Calculate Cutoff Frequency (Fco)
Select units of measurements:   inches   mm
Enter wide dimension of the waveguide:      
Enter narrow dimension of the waveguide:  

Select surface material of the waveguide:   Al   Au   Cu   Ag

Select units of frequency at which attenuation is to be calculated:   MHz   GHz
Enter Frequency:  

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