My N2PK VNA in transmision and reflection mode was used for the measurements. The following pictures show the basic measurement results. First I measured reference level for DUT open (blue curve). Then I terminated DUT port with precision 50 Ohms and measure isolation between Input and Output (red curve). The difference between both levels for each frequency gives Return Loss. Return Loss varies from -28dB to -38dB in the whole frequency range 2 - 60MHz. It is good result.
My bridge was primarily designed for intermodulation measurements. The most important quality parameter (except of Return Loss), is impedance matching between all ports and their terminations. Even when Output port termination is not critical for Return Loss measuring, when this port will be used for second signal generator connection during intermodulation measuring, its impedance matching will be very important for accurate measuring results.
That was the reason, why I added SWR measuring for all three ports to diagrams, too. SWR at all three ports input was better than 1.1 : 1. That is also good result. This Return Loss Bridge can be used for IM measuring also.