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Amity School of Engineering

Waveguide

Conventional transmission lines develop too much loss at microwave frequencies.Hollow waveguides present an alternative.Electromagnetic waves reflect from the walls of the wave guide as it travels its length.Brass, aluminum or silver plated.RECTANGULAR, elliptical and circular

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Amity School of Engineering

Overview of guided waves in TE, TM and TEM modes.

As frequency increases beyond the lower boundary that has been assigned as the microwave threshold (1 GHz) conventional R.F. techniques become less effective.Lead inductance and capacitance as well as connecting traces on substrates become issues affecting circuit performance.An example is TRANSIT TIME. Physical construction of devices must change.

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Amity School of Engineering

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Amity School of Engineering

Waveguide Modes

A waveguide operates most efficiently within modal boundaries.A given waveguide cross section will have a cutoff frequency where a signal below it will not propagate.What type of filter does this act as?Not all modes strike the walls at the same angle therefore the distance traveled varies.This is called multimode propagation.Effective velocity reduces.Pulse spreading results and subsequent pulses following closely will interfere. (Dispersion)

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Amity School of Engineering

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Amity School of Engineering

Modes of propagation

10TE# of variations along b

# of half cycles along a

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Amity School of Engineering

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Amity School of Engineering

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Amity School of Engineering

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Group velocity- used to determine the length of time a signal takes to travel the length of the waveguide.

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Amity School of Engineering

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Amity School of Engineering

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Phase velocity- used to determine wavelengt

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Amity School of EngineeringImpedance of a waveguide.

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Amity School of Engineering

The calculation for wavelength in a guide requires phase velocity.

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