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The cutoff frequency of an electromagnetic waveguide is the lowest frequency for which a mode will propagate in it. In fiber optics , it is more common to consider the cutoff wavelength , the maximum wavelength that will propagate in an optical fiber or waveguide .
The mode with the lowest cutoff frequency is the fundamental mode of the waveguide, and its cutoff frequency is the waveguide cutoff frequency. [ 15 ] : 38 Propagation modes are computed by solving the Helmholtz equation alongside a set of boundary conditions depending on the geometrical shape and materials bounding the region.
In radio-frequency engineering and communications engineering, a waveguide is a hollow metal pipe used to carry radio waves. [1] This type of waveguide is used as a transmission line mostly at microwave frequencies, for such purposes as connecting microwave transmitters and receivers to their antennas, in equipment such as microwave ovens, radar sets, satellite communications, and microwave ...
An optical waveguide is a physical structure that guides electromagnetic waves in the optical ... ARROW waveguide; Cutoff wavelength; ... Waveguide (radio frequency ...
Each mode appears above a precise cut-off frequency determined by the waveguide dimensions and the filling medium. For TM modes, decreasing the waveguide thickness (usually denoted as ) increases the cut-off frequency with /. In the case of SIW, the thickness is so low that the cut-off frequency of TM modes is much higher than the dominant mode.
The waveguide cutoff frequency is a function of transmission mode, so at a given frequency, the waveguide may be usable in some modes but not others. Likewise, the guide wavelength [h] (λ g ) and characteristic impedance [b] ( Z 0 ) of the guide at a given frequency also depend on mode.
Below cut-off the impedance is imaginary (reactive) and the wave is evanescent. These expressions neglect the effect of resistive loss in the walls of the waveguide. For a waveguide entirely filled with a homogeneous dielectric medium, similar expressions apply, but with the wave impedance of the medium replacing Z 0.
Extremely low frequency (ELF) (< 3 kHz) and very low frequency (VLF) (3–30 kHz) signals can propagate efficiently in this waveguide. For instance, lightning strikes launch a signal called radio atmospherics , which can travel many thousands of kilometers, because they are confined between the Earth and the ionosphere.
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