I would be interested to know how much the SVA1000X differs from the SSA3000X *HARDWARE WISE*.
Is it really a new hardware or could everything VNA related (in theory) been implemented by software?
Regards,
Vitor
This a all off the cuff, but it might be theoretically possible to use the SSA hardware (with caveats) - as only one of the LO's is actually sweeping, and that same LO is downconverted and used to generate the TG output. I don't think the hardware is the same though.
Therefore the phase relationship - after power up - between all of the PLL's - might not change between the TG output and the SA input as it sweeps (assuming nothing is altered). Since the LO1 which is sweeping the TG is also used to downconvert the input, the phase of that doesn't need to be consistent.
To do an OSL VNA measurement you at a minimum need to be able to do four sweeps where the phase doesn't change. One for the open, one for the short, one for the load, and one for the measurement. The problem arises if you reset or preset the SSA, then all of the PLL's will come back up at different phases and so your calibration needs to be done again.
The other caveat is that there is only one input, so there can be no reference measurement. This means that any drift will directly impact the measurement.
Real VNA's have at least two receivers - one is used as a reference - and the DUT measurement is compared against the reference measurement.
As a point of comparison the Signalhound products cannot maintain the phase relationship between the SA and the TG as they sweep - because they are physically different devices and only share a 10MHz reference, but don't share the same LO. They can make VNA type measurements at a single frequency (i.e. no sweeping) but the system only has only one receiver and so they have the drift problem above.
This could all be worked around somewhat using a solid state switch to provide a reference input and a DUT input and switch between them as needed to measure and correct for the phase issue on each frequency change, and it would also allow a correction for most of the drift issue. However the isolation of the switch would be an issue that would affect the measurement at some point and would need to be corrected for.