开云体育

I can chime in as a ME wearing an EE hat :) I see S11 measurement as essentially a shaker table measurement where you are not allowed to touch anything but the interface plane. Imagine a shaker and a load cell + an accelerometer between the shaker and the DUT. Or think of holding a short slinky hanging down from your arm. Close your eyes - you can only feel the interface plane. Shake it in various ways and you get the slinky’s S11 response.

Then stick a load cell with a test mass and another accelerometer stuck to it on the far end, and you get S12. Swap the ends and you can measure S22 and S21.

In one “interpretation”, the load cell measures the mechanical equivalent of current. The accelerometer measures the mechanical equivalent of voltage. In such interpretation (one of many), mass is the equivalent of resistance (I=V*R vs F=a*m). If we let acceleration represent a higher derivative of voltage, you can also find mechanical equivalents for capacitance and resistance. If we let the velocity be the equivalent of voltage, then mechanical damping becomes equivalent to real impedance, and inertia is equivalent to imaginary impedance. And so on, and pardon for mathematical mistakes here. But the gist of it is: you can certainly derive mechanical analogues of electrical circuits. The reverse of it was an actual job description not too long ago, when analog computers simulated mechanical systems and were used to model such.

In an S-parameter test set - and anyone actually knowing what they talk about please correct me - directional couplers and RF switches do the job of separating the energy flow out of a port from the flow into the port.

Circulators are a particularly clever kind of a directional coupler that’s connected back to itself (at least I think of them that way) - the energy can make it all the way back to the 1st port if the ports on the way reflect it “back” - back into the respective ports, but forward in the circulator (there’s an arrow on it that shows which way is “forward”, at least on the few I got). A circulator is the RF equivalent of a lazy Susan :)

The “problem” with bare VNAs is that the S-parameter test set is a separate device, and a costly one from what I gather, yet one without which the capability of the VNA is quite untapped. The “bare” VNA is the RF power source and one or more fancy vector voltmeters. A test set is what connects those up in a circuit that allows a particular kind of very useful measurements (one- and two-port S-parameter measurements). It’s what lets you use those load cells and accelerometers for something useful :)

Best not let the ME ramble too much, though.
Cheers, Kuba