Читать книгу Handbook of Microwave Component Measurements - Joel P. Dunsmore - Страница 90

S‐parameter measurements of devices provide the common reference for RF and microwave circuit and system analysis. While the basic methods of S‐parameter measurements were developed decades ago, many advances have occurred in just the last five years that makes obsolete the common understanding of the capabilities and limitations of these measurements. Vastly improved hardware and software capabilities provide for control of stimulus signals and analysis of response signals that allow measurement systems to extend the basic linear S‐parameters to multiport, differential, and non‐linear characteristics. In the past, S‐parameters were limited to two ports; now up to 32‐port systems are readily available. In the past, measurements were limited to linear responses; now non‐linear, distortion, noise, and even load pull characterizations are possible. In the past, calibration techniques were restricted to a few limited sets of standards and algorithms and limited to devices with the same input and output frequencies; now a wide range of calibration algorithms and applications can be applied to a variety of components, with few restrictions.

A clear understanding of the underlying architecture of a vector network analyzer (VNA) is necessary to understand the full capabilities and limitations of the modern VNA. The first part of this chapter deconstructs the VNA to discuss the individual block diagram elements, their attributes and deficiencies, and how they operate together to provide the capability and applications described in later chapters. In the history of VNAs, the HP 8753 and the HP 8510 were the industry‐leading RF and microwave VNAs of the 1980s and 1990s, from which many of the principal understandings of capabilities and limitations were formed. For that reason, many of the characteristics of these analyzers are discussed in the following sections to provide a context for the discussion of the modern VNA attributes. In almost all cases, many well‐known limitations of these products no longer apply, and a key goal of the first section of this chapter is to illuminate to the reader these improvements.

By around the year 2000, an arms race of sorts emerged in the world of VNAs with the nearly simultaneous introduction of the PNA and ENA families from Agilent, the Ballmann S100, the ZVR and ZVK from Rohde‐Schwartz, the Lightning™ and Scorpion™ from Anritsu, and the 3765 from Advantest. By 2010, Agilent and Rohde‐Schwartz advanced to the modern generation of multi‐function component test platforms, the PNA‐X and the ZVA, while Anristu's products remained mostly in the area of linear S‐parameter test in the form of the Vectorstar™. As the author is a principle designer and architect of the Keysight products, the details on the VNA architecture, structure, and capabilities described here are derived from this knowledge. But many of the factors discussed apply equally well to all measurement systems, regardless of manufacturer, including custom‐built systems sometimes seen in university research labs or national standards laboratories. Because of these advancements, many rules of thumb and common understandings based on the first generation of commercial VNAs are no longer relevant.

The second portion of this chapter describes the wide range of measurements and characteristics that can be derived from the basic measurements. In Section 2.3, the basic functionality for making measurements is described along with real‐world issues and errors that affect these measurements. Particularly in VNA‐based measurements, many of these errors can be characterized during a calibration process, and error correction can be applied to the results to remove, to a great extent, the effects of these errors. The calibration and error correction process will be described in detail in Chapter 3. Detailed descriptions of measurements of particular devices are covered in subsequent chapters: linear devices (Chapter 5), amplifiers (Chapter 6), mixers (Chapter 7), and balanced devices (Chapter 10).

Author's notes on the second edition: The evolution of VNA architecture has dramatically increased since the first edition was written in 2011. Almost all VNAs on the market today have a full reflectometer on each port, so the discussion the three‐receiver architecture presented in the first edition of this book (principally the architecture of the HP 8753) has been greatly reduced to make room for more interesting VNA enhancements such as true multiport.