I tried to use a single directional coupler to create a reflectometer and was hoping to measure both amplitude and phase of reflected signal.
My setup is a follows:
The directional coupler is from MiniCircuits ZFDC-10-182-S+
I have tested my design with different loads, 0R, 50R, 100R, 100R||3.3pF ect.
But only the magnitude (VMAG) measurements are correct, the phase (VPHS) measurements does not seems to be correct. And I cannot find any relation, between different loads and expected vs. measured phase.
So should it possible to measure phase information with a directional coupler?
Or am I doing it wrong ?
50R: VPHS=0.88V, VMAG=0.16V
Open: VPHS=1.500V, VMAG=0.76V
Short: VPHS=0.282V, VMAG=0.69V
100R: VPHS=1.455V, VMAG=0.50V
100R||10pF: VPHS=0.58V, VMAG=0.66V
100R||3.3pF: VPHS=1.18V, VMAG=0.57V
Edit: My open load now seems correct, before I measured open load as "no load" in the cable, but this resulted in a capacitance in the cable end SMA connector. I have now made an open load as an trimmed down SMA connector. I still don't get why the magnitude i higher, but that is maybe related to the load on the source being changed.