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Waveguide with Tunable Length

Principle of a waveguide with a tunable length -3dB-Coupler shorting plunger

Figure 1: Principle of a waveguide with tunable length

Certainly you can visualise a waveguide, changing its length like a telescope...
...but the electric contact between the waveguide walls will be a seriously problem. Additional the cross-sectional area of the waveguide must't changed to avoid reflections. This would be possible in a theoretically ideal case only. This one waveguide section will be a source of reflections definitely!

A better way is using a short-circuited waveguide and a -3dB-coupler. By the calculating of the waveguides length you must take into account the phaseshifting of 180 degrees on the occasion of the reflection at the short-circuited end of the waveguides!

Describing of the function:

Figure 2: shorting plunger with ferrites

shorting plunger with ferrites

Figure 2: shorting plunger with ferrites