On microwave measurement of S-parameter using ring hybrid rat-race circuit

Using a single ring hybrid and a cascaded double ring hybrid microwave circuits, a set of equations have been derived in terms of measured output powers at the difference or sum ports of the ring hybrid. These equations can be used straightforward to compute the reflection and transmission coefficients of a device under test. In comparison with a modern microwave network analyzer, this ring hybrid measurement method together with a set of derived equations offers a simple and very low cost technique for S-parameter measurement.