Interpretation Of Electrical Test Data With Regards To Microwave Cable Assemblies
By Dave Slack
A cable assembly provides two essential functions in a microwave or RF system. These devices serve to mechanically connect an RF source to its load and to serve as a propagation medium and waveguide for the RF signal.
A cable assembly should not be considered as hookup wire. It is a passive, TEM mode, microwave device. As such, they are system components whose performance is just as important as directional couplers, combiners or antennas or a host of other passive microwave components. Cable assemblies are an integral part of the microwave system and their performance is critical to overall system performance.
To ensure that the cable assembly being considered for use in a given system will perform well several measurements of electrical performance are commonly made. The primary measurement parameters used when evaluating microwave cable assemblies are voltage standing wave ratio (VSWR) and insertion loss. These are commonly referred to in quantitative terms where specifications such as VSWR of 1.4:1 maximum and insertion loss less than 1.5 dB.
While these numerical quantities are of great importance, especially when making a passfail judgment, they do not tell the whole story. When attempting to understand why a cable assembly is not meeting its quantitative requirements it is enormously valuable to understand the qualitative features of the insertion loss and VSWR characteristics. A quick glance at an insertion loss and VSWR plot can yield an abundance of understanding with regards to a cable assembly's fitness for use.
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Source: Times Microwave Systems