Wireless Multi-Port Sensing: Virtual-VNA-Enabled De-Embedding of an Over-the-Air Fixture

We develop a multi-port-backscatter-modulation technique to determine, over the air (OTA), the scattering parameters of a linear, passive, time-invariant multi-port device under test (DUT). A set of "not-directly-accessible" (NDA) antennas can be switched between being terminated by the DUT or by a specific, known, tunable load network. Waves can be radiated and captured via a distinct set of "accessible" antennas that couple OTA to the NDA antennas. First, we characterize the OTA fixture between the accessible antennas' ports and the DUT's ports. We achieve this based on our recently introduced "Virtual VNA" technique; specifically, we connect the NDA antennas to the tunable load network and measure the scattering at the accessible antennas' ports for various configurations of the tunable load network. Second, we connect the NDA antennas to the DUT and measure the scattering at the accessible antennas' ports. Third, we de-embed the OTA fixture to retrieve the DUT's scattering parameters. We experimentally validate our technique at 2.45 GHz for 1-port DUTs and 5-port DUTs, considering a rich-scattering OTA fixture inside a reverberation chamber. We systematically study the influence of the number of accessible antennas and various conceivable simplifications in terms of the system model as well as the properties of the tunable load network. Our wireless multi-port sensing technique can find applications in areas like RFID and wireless bioelectronics.