Waveguide Calculator. A rectangular waveguide is a hollow metal tube used to carry microwave signals — its physical dimensions determine which frequencies it can transmit. Enter your broad wall width (a), narrow wall width (b), operating frequency, and TE mode (m, n) into the Waveguide Calculator to find the cutoff frequency for your selected mode. Secondary outputs include guide wavelength, wave impedance, and attenuation constant. Also try the calculate Step Attenuator.
The cutoff frequency is the minimum frequency required for a specific TE or TM mode to propagate through the waveguide. Below this frequency, the mode is evanescent and cannot propagate. See also our Antenna Near Field Calculator.
The dominant mode in rectangular waveguides is TE10, which has the lowest cutoff frequency. This mode is most commonly used in practical applications because it can propagate at the lowest frequency.
The cutoff frequency is inversely proportional to the waveguide dimensions. Larger dimensions result in lower cutoff frequencies, while smaller dimensions increase the cutoff frequency.
When the operating frequency is below the cutoff frequency, the electromagnetic wave cannot propagate and is rapidly attenuated. The mode becomes evanescent and decays exponentially along the waveguide.
Guide wavelength is always longer than the free space wavelength at the same frequency. It represents the distance between two points of equal phase along the waveguide and depends on both frequency and waveguide dimensions.
Wave impedance is the ratio of transverse electric field to transverse magnetic field in the waveguide. It varies with frequency and is different from the characteristic impedance of transmission lines.
Rectangular waveguides are easier to manufacture, have better mechanical stability, and allow for simpler coupling mechanisms. They also have well-defined polarization and no degenerate modes in the dominant TE10 mode. You might also find our Pi Attenuator Calculator useful.