Fundamentals of Vector Network Analysis

Oct. 11, 2007
Vector network analysis (VNA) is among the most essential of RF/microwave measurement approaches, and Rohde & Schwarz (www.rohdeschwarz. com) is among the world’s leading manufacturers of test equipment for this purpose. While the firm is ...

Vector network analysis (VNA) is among the most essential of RF/microwave measurement approaches, and Rohde & Schwarz (www.rohdeschwarz. com) is among the world’s leading manufacturers of test equipment for this purpose. While the firm is associated with a wide range of high-performance test equipment, including spectrum analyzers, signal generators, and telecommunications test systems, few readers would think of the company as a supplier of technical text books. But Rohde & Schwarz has devoted a section of its website, appropriately named “Book Shop,” to the sales and promotion of its own books, including the recently released Fundamentals of Vector Network Analysis by Michael Hiebel.

Fundamentals of Vector Network Analysis is the second edition of a text originally published in 2005. It is suitable for both beginners as well as experienced users of VNAs and is meant to supplement technical papers, application notes, and owner’s manuals in learning the fine art of operating a microwave VNA. The text begins simply, with explanations of wave quantities and scattering parameters (S-parameters) used to describe transmitted and reflected signals through a network. It includes a block diagram for a heterodynereceiver- based VNA with an arbitrary (N) number of ports. The block diagram includes a test set that is used to separate the incident and reflected signal waves, a generator that produces the stimulus signals for testing, two separate receivers for comparing signals in the reference and measurement channels, and a computer for performing vector error correction and other signal processing.

As part of its operation, a heterodyne VNA downconverts test signals to lower-frequency intermediate-frequency (IF) signals with the help of a low-noise local-oscillator (LO) source. The IF signals are then sampled and digitized by a high-speed analog-to-digital converter (ADC). Converters used in VNAs generally provide at least 14-b resolution, with higher resolution possible through the use of various techniques, including dithering.

The book is an excellent source of theoretical as well as practical information on microwave VNAs and their operation. For those interested in theory, derivations are provided for the mathematics presented in the text. For those more concerned with practical matters, the book reviews the importance of the main instrument settings and even provides a step-by-step review of a typical instrument user interface (the Rohde & Schwarz ZVB VNA). Settings include sweep type, sweep range, number of points, IF bandwidth, sweep time, and marker settings.

Numerous remote-control options are detailed, including the use of protocol-based interfaces such as GPIB and the local-area network (LAN). Automation through the Standard Commands for Programmable Instruments (SCPI) language is also covered, with a review of the unified instrument model based on the use of the SCPI standard for automation and remote control of test instruments.

Measurement accuracy is an important topic whenever using a VNA, and the text devotes better than 70 pages to the subject. It highlights various sources of measurement errors, such as thermal drift and the challenges in achieving good measurement repeatability with imperfect mechanical devices, such as cables and connectors. It covers nonlinear systematic measurement errors, such as compression effectives, as well as linear effects. It also provides techniques that can be applied to correct these errors, such as the use of different calibration techniques and precision calibration standards for both measurements on devices with connectors and on wafer. Mathematical expressions are given for the basic calibration standards, such as line, short, open, match, reflect, and through standards, and even waveguide calibration standards are detailed for higher-power and higher-frequency measurements through millimeterwave frequencies.

The text steps a reader through various different 10- and 12-term calibration error approaches, including calibration solutions for a device under test (DUT) that is categorized as a noninsertable device (requiring an adaptor of some kind). It also describes several “incomplete” calibration approaches, including the use of normalization to improve accuracy and the one of a one-path, two-port calibration technique. One of the more useful sections in the book includes several tables that show the influence of various actions, such as the modification of the test port output level or the IF bandwidth, on a calibration.

Several sections of the book are devoted to nonlinear measurements as well as measurements that require some form of frequency translation, such as on mixers. Although published by a notable test-and-measurement equipment manufacturer, the book does not go out of its way to promote Rohde & Schwarz gear but, in fact, provides a sound technical background on the functions and operation of one of a microwave engineer’s most valuable test tools, the VNA. The 419-page, hardcover book can be purchased for 68 Euros (approximately $96.75 US) directly from the main Rohde & Schwarz website at

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