5 - Vector network analyzers

Summary

Introduction

The VNA is the instrument that measures the S-parameters (and related quantities) of passive and active devices and components. The phase and magnitude of these S-parameters are displayed in different formats in accordance with the user's application. Scalar network analyzers measure only the magnitude of the device's performance and that is not the focus of this chapter.

VNA measurements can be done using one or many ports, over swept frequency or swept power and with a variety of receiver configurations, depending on the measurement requirement. This chapter explores the history of this instrument, some aspects of its structure and performance, and a brief introduction on how specific measurement applications are affected by the VNA attributes. Many microwave measurement concepts and instruments are based on theVNA and some are discussed later in this book. As such, this chapter serves as something of an introduction to many subtopics.

History of vector network analyzers

Pre-HP-8510 VNA – 1950–1984

Rohde and Schwarz introduced the first impedance measuring device that could warrant the term “network analyzer” in 1950. Wiltron introduced the 310 VNA in 1965. This was followed by the HP VNA in 1966, 1968, and 1970.

Table 5.1 shows the VNA model numbers and the years for this time period. In [1], Doug Rytting describes in detail these early VNAs.

During this period, sweepers were used as narrow-band sources (2–4 GHz, 4–8 GHz, etc.). The displays shown on the monitor were rectangular or Smith Charts. External computers were used to control the measurements and displays. To cover the 2–20 GHz frequency range, multiple sources were used. Calibration was done manually with external calibration kits.