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I have recently measured the standing wave signal from a waveguide. I notice that as the frequency is lowered the signal tends towards a sawtooth wave.

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My guess for why this happens is that the EM wave is affecting the magnetisation of the ferrite material isolator. Is this correct and if so what exactly is happening? I can't seem to find many resources on this effect. I am using the marconi ferrite isolator type 6034.

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  • \$\begingroup\$ What are the plots? Amplitude vs. position of a slotted waveguide? \$\endgroup\$ Mar 12, 2023 at 6:10
  • \$\begingroup\$ Current vs position using a E-measuring probe connected to an ammeter. \$\endgroup\$
    – dk30
    Mar 12, 2023 at 13:29

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A waveguide has a minimum cutoff frequency below which waves do not propagate (not counting near-field effects).

Any waveshape other than a pure sine contains higher harmonics. For example, a square wave is the fundamental + 1/3 its amplitude in the 3rd harmonic + 1/5 the 5th harmonic + 1/7 the 7th... A sawtooth or ramp waveform contains all harmonics, both odd and even. Though the fundamental frequency may be too low to propagate in the waveguide, harmonics can. If the generator produces some harmonics, or if they're created by some nonlinear component, e.g., a rectifier diode, then that is what emerges from the other ennd of the pipe.

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  • \$\begingroup\$ The signal was produced using a gunn diode and the frequency used was selected with an adjustable cavity resonator. Is it the case that at lower frequencies the selected frequency is attenuated in the guide while the higher harmonics can propagate? I specifically asked about the ferrite isolator as I was told that this results in non-linear behaviour. \$\endgroup\$
    – dk30
    Mar 12, 2023 at 2:11

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