Waveguide With Dispersion Compensation - Anritsu MS2024B Manual

Time Domain, Option 2 8-3 VNA Master Implementation

Waveguide with Dispersion Compensation

Waveguide media suffers from frequency dispersion, which basically means that signals at
different frequencies that are launched at the same time into a waveguide will arrive at
different times at the output of that waveguide. This phenomenon is not evident when looking
at the frequency response of the waveguide. When looking at the time or distance response,
however, you will see the effect of this dispersion. The VNA Master uses a special
frequency-to-time conversion technique to compensate for this dispersion in waveguide
media. This compensation is applied only in the distance domain.
Figure 8-9 shows the reflection response (S ) from a 32 cm-long waveguide. The distance
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response shows a sharp peak at 32 cm, as expected. The time domain response shows a
spread-out peak at approximately 1.17 ns, which is the equivalent of 35 cm distance. Ideally,
the S time domain response should be equivalent to the distance domain response. Because
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of the dispersion, however, the time domain response is spread out and inaccurate. The
distance domain response, which has dispersion compensation, produces the corrected
response. FGT is used in this screen capture to again illustrate how gating a DUT in the time
domain will smooth out its response in the frequency domain. (Compare the measured
response in TR4 with the FGT modified version shown in TR1).
Figure 8-9. S Measurement of 32 cm Long Waveguide Showing Dispersion Compensation
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Vector Network Analyzer MG PN: 10580-00289 Rev. K 8-11