Understanding Specsmanship

July 29, 2004
Some manufacturers are to be applauded for their efforts to provide as much data (for a comparison) as possible.

Power dividers/combiners are considered "essential" components by most amplifier designers. Now available at RF and microwave frequencies in a wide range of packages from roughly 100 suppliers (not to mention distributors), these versatile components allow the combining of multiple power transistors in a high-power-amplifier (HPA), for example, or the splitting of signals two, four, or almost as many ways as desired. A Special Report beginning on page 33 details some of the things to look for when selecting a power combiner/divider.

In the midst of poring over hundreds of data sheets of research on power dividers (tirelessly collected and captured from websites by Editorial Assistant Dawn Prior), it became apparent that specifications are not always what they seem. The two obvious examples of this are two of the power divider/combiner "quality" specifications: amplitude unbalance (or balance or tracking) and phase unbalance. While almost every manufacturer standardizes the way they present their own data, comparing data between different manufacturers can sometimes be a challenge. For these two specifications, for instance, many manufacturers choose to present their performance levels in terms of a deviation, such as ±0.3 dB for amplitude unbalance and ±6 deg. for phase unbalance. But just as many manufacturers present these same two specifications as the total range of unbalance, namely, 0.6 dB for amplitude unbalance and 12 deg. for phase unbalance. And in some unfortunate cases, suppliers list what appears like it should have been a deviation, such as ±0.5 dB for amplitude unbalance, as simply 0.5 dB.

Some manufacturers are to be applauded for their efforts to provide as much data (for a comparison) as possible. Mini-Circuits (Brooklyn, NY, www.minicircuits.com), for example, is one of the few power divider/combiner suppliers that include a set of S-parameter data for their components. This data shows values that are considerably higher (certainly not an advantage) than those of competitors, because the data also include division losses (along with the expected insertion loss). While making their products appear to have worse performance (if not properly compared) than a competitor, these data are useful to designers who must consider all losses in a microwave link budget, for example.

Until the industry agrees on a standard format to present data, power divider/combiner specifications (including CW and peak power) must be interpreted before they can be meaningfully compared. But while there is room for interpretation, there is room for specsmanship and unfair comparisons.

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