![low-cut off wavelength low-cut off wavelength](https://vos.noaa.gov/MWL/aug_07/Images/figure2_cutoff_big.jpg)
#Low cut off wavelength free#
The guide wavelength in waveguide is longer than wavelength in free space. For example, if you are making a PIN diode switch with two shunt diodes spaces 3/4 wavelength apart, use the 3/4 of a guide wavelength in your design. Guide wavelength is used when you design distributed structures in waveguide. Here's the equation for guide wavelength: The guide wavelength is a function of operating wavelength (or frequency) and the lower cutoff wavelength, and is always longer than the wavelength would be in free-space. Guide wavelength is defined as the distance between two equal phase planes along the waveguide. See our page on waveguide loss for more information. Remember, at the lower cutoff the guide simply stops working. Thus for WR-90, the cutoff is 6.557 GHz, and the accepted band of operation is 8.2 to 12.4 GHz. The accepted limits of operation for rectangular waveguide are (approximately) between 125% and 189% of the lower cutoff frequency. We'll let you do the math on this (multiply lower cutoff frequency by two.) now it's time for another Microwaves101 rule of thumb: Waveguide operating band The upper cutoff frequency is exactly one octave above the lower. Thanks for the correction, Jean-Jacques!) The upper cutoff wavelength (lower cutoff frequency) for this mode is very simply: The usual mode of transmission in rectangular waveguide is called TE10. All microwave textbooks will tell you about this, but we don't really care. Waveguide can support many modes of transmission. Note that in the equations on this page we have kept the units simple and consistent, and you might want to do the same. Here is an index to the subject of waveguide mathematics: This page contains some of important equations for rectangular waveguide. Our other info on waveguide can be found on these pages: