A Prototype Distributed Six-Port Reflectometer-Based Transmission-Only Vector Network Analyzer

A novel distributed Transmission-Only Vector Network Analyzer (TVNA) based on two Six-Port Reflectometers (SPRs) is experimentally verified. The prototype distributed SPR-TVNA measures S21 and operates with two independent RF sources, allowing the two ports of the Device Under Test (DUT) to be widely separated with no common cables coming to a central location. Using the distributed SPR-TVNA allows for measurements of, e.g., distantly separated antennas, or taking grain bin imaging measurements that would otherwise require long coaxial cables. A key issue of these large DUTs is accurate measurement of the through-measurement, S21. The distribution (separation) of the two RF sources in the SPR-VNA requires novel procedures to obtain accurate results. The results are confirmed using simulations and experiments, with the experimental results obtained using custom-built hardware. While, in theory, a full VNA can measure S11 and S22, which is confirmed through simulation, the experimental results show significant errors in S11 and S22. We thus call the current device a Transmission-Only VNA. The fundamental math of the SPR-VNA means there is a ±180° phase uncertainty that must be solved, e.g., via a wide-band sweep looking for phase jumps. The experimental S21 measurements of the prototype show maximum errors of 1.5 dB in magnitude and 6 degrees in phase over a bandwidth of 0.6–1.2 GHz.