The present invention relates, in general, to the field of precision scalar network analyzers. More particularly, the present invention relates to a swept microwave power measurement system and method which determines "absolute" power by applying an interpolated correction factor determined at any given frequency during a sweep to the "apparent" power output at a predetermined frequency.
In the past, scalar analyzers have been used to measure magnitude only reflection and transmission characteristics of microwave components. The relatively low cost, high speed and simple operation of scaler analyzers have been their fundamental attraction. However, their limited power measurement accuracy (+/-1 to 2 dB) have often kept them in the role of qualitative limit line testing or intermediate screening devices instead of being capable of more precise quantitative analysis.
Therefore, it has been necessary to use scalar analyzers in association with accurate, high performance power meters when accurate power measurement is required. This is necessitated by virtue of the fact that a conventional scalar network analyzer does not have the capability of accurately measuring microwave power, since scalar measurements are, per se, power ratio measurements. It is for this reason that active component manufacturers are forced to make power measurements with a separate instrument such as a microwave power meter. In addition to the added equipment cost, this operation involves considerable extra measurement time per part. Nevertheless, the combination of a scalar analyzer and a power meter still renders it very difficult to make exact measurements of power level at many different frequencies without laborious effort on the part of an operator and swept absolute measurements are impossible.
It would therefore be highly desirable to incorporate an accurate power measurement capability into a scalar analyzer. Further, the ability to make high performance, swept absolute power measurements would be a fundamental advantage. Absolute power measurements are required to set up critical drive levels to components such as mixers, or to measure critical output levels such as the compression point of amplifiers. And, while absolutely flat linearity is essential for ratio and relative measurements conventionally made by scalar analyzers, more is demanded for absolute power measurements. The two major specifications for such a system would be an accurate, traceable 1 mW calibration reference to set absolute power at a known frequency (which is typically 50Mhz) as well as an accurate frequency response curve for the power sensor.