@xaxaxa,
The effort that you have with two ADF's will bring you the
advantage not to make measurements with square signals
but with proper sinus signals.
The ADF chip family provides a clean vco signal from 0.5fmax
to fmax when not using the internal divider.
So you are able with the ADF4350/51 to generate 2.2-4.4GHz
in good spectral purity.
With two of these chips you could fix one to 2.2GHz and do a
range tuning from 2.2 to 4.4 GHz with the second one.
Mixing both sigs you get depending on your LPF or HPF
you use (or even make them switchable) DC- <2.2GHz
or/and 4.4 - 6.6GHz and if disabling the fix freq. ADF
you will get 2.2-4.4 GHz.
So it's up to you which effort you would like to do.
Btw not knowing if you know the link (German doc concerning
the scalar Analyzer with ADF4350/51 from BG7TBL found
on Ebay) :
https://www.agaf-ev.org/agaf-de/NWT4000-AGAF.pdfThis doc covers the problem using rectangular sigs for
measurements. And for vactorial measuremts this issue
is much more important to care about concerning reliable
results.
What concerns the SVA1015X - I think they will reduce
the price in the future and the Siglent device have the
advantage that you could enable all options by hacks you
find in this forum easily.
Markus