Microwave Journal 50 Year Retrospective Series: VNA Evolution

Microwave Journal 50 Year Retrospective Series: VNA Evolution - A European Perspective

Many years ago when our grandfathers used slotted lines to analyze networks, they may have dreamed of simpler, less cumbersome instruments. Measurements with a slotted line were very time consuming, primarily due to the fact that the maximum and minimum of the standing-wave pattern and the exact distance between the first minimum and the reference plan had to be detected manually.

On top of that, the complex reflection coefficient had to be calculated using the relevant formulas or tables. Nevertheless it was an important instrument in its time and Figure 1 shows a slotted line, which was one of the first products produced by the RF company that Dr. Rohde and Dr. Schwarz established in 1933, which was later to be known as Rohde & Schwarz.

The company’s Z-g-Diagraph shown in Figure 2 was the first instrument to directly indicate the complex S-parameters without the need for additional calculation. This is why it merits the name vector network analyzer, although this term was not yet defined in the early 1950s when the instrument was launched. Together with a later model, a frequency range of up to 2.4 GHz was covered and the instruments became famous all over the world.