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6.5: Summary

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    41067
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    Rectangular waveguides guide EM fields in a rectangular pipe. Parallel plate waveguides are unintentional but are approximated by the planar conductors found in printed circuit boards. Rectangular wave equations describe propagation in these structures and are derived from Maxwell’s equations by applying multiple simplifications such as using phasors, restricting propagation to just one direction, and applying symmetries. Important concepts that flow from the rectangular wave equations are that rectangular and parallel-plate waveguides support multiple modes, i.e. variations of the EM field, with all but the TEM mode having a finite cut-off frequency below which a particular mode cannot propagate. The rectangular waveguide does not support a TEM mode, a mode with no variations of the field between boundaries, so the rectangular waveguide cannot support a propagating mode below the lowest cut-off frequency. A mode with more variations of the field will have a higher cut-off frequency. A separate physical result is that if two modes can propagate the EM energy will be equally partitioned between them. Thus if two or more modes can propagate the information will become garbled since different modes travel at different speeds. This is observed in practice so for example, with rectangular waveguide the useful frequency range of operation is between the cut-off frequency of the mode with the simplest field variation, and hence the lowest cut-off frequency, and the cut-off frequency of the next higher-order mode.

    clipboard_e87f696dde24156a9b06e4b71ccac5683.png

    Figure \(\PageIndex{1}\): Rectangular waveguide hybrid.


    This page titled 6.5: Summary is shared under a CC BY-NC license and was authored, remixed, and/or curated by Michael Steer.

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