Low-Complexity Wireless Multi-Port Sensing by Multiplexed De-Embedding of an Over-the-Air Fixture

Abstract: Wireless multi-port sensing remotely retrieves the scattering matrix of a multi-port device under test (DUT) connected to a set of not-directly-accessible (NDA) antennas that couple over-the-air (OTA) to a set of accessible antennas. If (i) the OTA fixture characteristics are known, and (ii) the number of independent measurements at the accessible antennas is sufficient, the OTA fixture can be de-embedded to recover the DUT characteristics. In recent prior work, we solved (i) by connecting the NDA antennas to a specific known tunable load network (TLN). Here, we tackle (ii) by additionally using the TLN to provide measurement diversity. The connection between OTA fixture and TLN constitutes a programmable fixture (PF). When the DUT characteristics cannot be identified based on a single PF realization, we add measurement diversity with multiple PF realizations. The underlying "multiplexed de-embedding" achieves the joint de-embedding of an ensemble of PF realizations when a single PF realization cannot be de-embedded. We experimentally demonstrate our concept by remotely estimating the scattering matrix of a reciprocal, non-unitary 4-port DUT (10 complex-valued unknowns) via a rich-scattering OTA fixture purely based on measurements of a single transmission coefficient between two accessible antennas across 30 different PF realizations. We systematically study the trade-off between the number of independent measurements at the accessible antennas and the number of PF realizations. Multiplexed de-embedding of the OTA fixture paves the path to implementing wireless multi-port sensing with low hardware complexity in areas like RFID and wireless bioelectronics.