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Frequency Sweep (External Coupler) Mode
In the upper graph you see the reflection of the IF filter in VSWR format. Even
outside its passband the VSWR of the filter is quite good – this indicates that
the input impedance of the filter in the measured frequency range is very
close to 50 Ω in general. The lower graphs shows the impedance of the IF
filter in polar format, the so-called polar curve.