A High Performance Millimeter Wave Vector Network Analyzer System

There is an increasing demand for measurement capability at frequencies beyond 18 GHz and whilst some of this can be met by scalar measurement systems, many applications require vector information. At present, there are two established techniques for making vector network analyzer measurements at millimeter wave frequencies[ I]. The simplest employs a conventional super heterodyne network analyzer with samplers capable of operating up to 18 GHz and an up-convert/down-convert scheme to provide an r.f. signal to the device under test whilst ensuring that the system remains phase-locked to a signal within the allowable operating band. The scheme tends to suffer from limited dynamic range and poor phase accuracy because of the use of a free-running local oscillator and poor tracking of reference and test channels. The major advantage of the arrangement is that it allows the capabilities of an existing analyzer to be extended at low cost.