In coaxial cable construction, the correct impedance is controlled by the inner and outer conductor dimensions and the dielectric material separating the two conductors.
A dielectric material exhibits achieved Velocity of Propagation (VP ) relative to the speed of light and a Dielectric Constant based on the material selected and the amount of air (or not) created within the construction.
Typically, cables with a solid dielectric will have a Low VP, and cables with a foamed or taped dielectric material�which allows for the introduction of more air�will have a higher VP.
In delivering Phase Matched assemblies, the selected cable type or construction must be carefully screened to ensure a consistent VP between cable batches.
This allows the electrical length tolerance to be achieved within mechanical length tolerance, an important consideration if cable assemblies are to be deployed in phase sensitive applications such as phased array radar.
In practice, cables are pre-conditioned for mechanical and thermal stability to minimize transmission line changes, keeping electrical length deviation to a minimum. With this achieved, cable assemblies can be manufactured using either Absolute Matching or Relative Matching.
Absolute Matching means that any assembly taken from stock can be inserted into a phased array module or used as a replacement for a damaged cable.
Relative Matching is an alternate, and at times more economical, approach where assemblies are matched relative to one another in batches.
To achieve either standard, especially at higher frequencies, it�s critical to begin with raw cable delivering highly consistent VP between batches. In addition, the actual manufacture of the assemblies must be controlled in such a way as to maintain that high consistency.
At TSM we have semi-automated, programmable measurement equipment for phase matching. This equipment utilizes cutting tools that can achieve very close tolerance in Phase Matched sets of assemblies.
Where a rule of thumb in the past was to determine a tolerance of 1 degree per GHz, today it�s not unusual to produce assemblies at 18 GHz with a matching tolerance of +/- 4.5 degrees (or 0.5 degree per GHz).
Given the high levels of consistency in our manufacturing processes, as well as in the quality control of raw material between cable batches, TSM can be counted on to satisfy your phase matching requirements in a cost effective, efficient manner.
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