The 'Six-port' network analyser
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The (vector) automatic network analyser (ANA) was introduced. Moreover, it was noted that a key element in its (usual) implementation is a detection system which provides both amplitude and phase response. This generally calls for a heterodyne detection system, possibly involving multiple frequency conversion and the associated local oscillators etc. In practise these components make a substantial contribution to the overall complexity and their realisation becomes increasingly difficulty as one moves into the millimeter wave region. Much of the earlier technology which it replaces was, by contrast, built on a much simpler detection system whose response was to amplitude (or power) only. Here the need for phase response can be avoided in certain problems by the use of techniques based on tuning transformers. However, these are both frequency sensitive and time consuming. The so-called 'six-port' technique represents an attempt to combine the better features of the two technologies. In particular, the simplicity of the detection system is retained, while the phase response is achieved (and the tuning requirement eliminated) by the use of additional (usually a total of four) detectors.