Hello, is there a possibility to combine 2 nanoVNA to create a 4 port VNA which than can be used also to measure balanced circuits using modal decomposition techniques, i.e. measure common mode (Scc11, Scc22, Scc21, Scc12) and differential mode (Sdd11, Sdd22, Sdd21, Sdd12) and mode conversion (Sdc11, Scd11 etc)  S-parameters
Thansk
Thomas

On 5/24/22 5:33 AM, thomas.haehner@nexans.com wrote:
> Hello, is there a possibility to combine 2 nanoVNA to create a 4 port
> VNA which than can be used also to measure balanced circuits using
> modal decomposition techniques, i.e. measure common mode (Scc11,
> Scc22, Scc21, Scc12) and differential mode (Sdd11, Sdd22, Sdd21,
> Sdd12) and mode conversion (Sdc11, Scd11 etc)  S-parameters
> Thansk
> Thomas
> _._,_._,_


I think you'd need a bunch more than 2 nanoVNAs.  Each NanoVNA measures
two parameters (S11, S21)  a full two port has 4 parameters (S11, S21;
S12, S22), so it requires a pair of NanoVNAs.  A 4 port needs *16*
parameters which would need 8 NanoVNas.


However, some clever relay networks might let you get away with one 2
port VNA - you'd need to switch terminations on the unused ports, etc. 
If you've got a bunch of cheap relays (or you're working at HF, where
most relays would work), you can probably do it.  After all, people make
4 port measurements with 2 port VNAs all the time.  Having 5 receivers
just makes it faster.

For these "many port" applications, another approach is to share the
reference signal across N copies, and disconnect the sources on N-1 of
them. This is much like folks using a common clock for multiple channel
ADCs or common reference oscillator for RTL-SDRs, etc.

At some point, it's easier to just buy more $50-100 boards (after all,
they don't need displays or batteries) and brute force it.


I'll also point out that calibrating a 4 port VNA is something that will
make you seriously consider building an ecal box with relays. Open,
Short, Load x4, thru x 16, etc. That's a lot of mating and demating
connectors. (BTDT)