RF and Microwave Circuit Design

7Measurements

7.1 Introduction

As the operating frequency of electronic circuits increases into the RF and Microwave region measurement techniques become more complex, and additional care is needed both in using the correct measurement procedure and in the care of measurement instrumentation. Whilst there is an extensive range of specialist high-frequency test instrumentation available for measuring specific parameters such as frequency and power, the core measurement system in any RF or microwave laboratory is the network analyzer. The primary function of a network analyzer is to measure and display the S-parameters of a passive or active circuit. The majority of network analyzers are two-port instruments, which can measure the properties of a two-port device-under-test, although multi-port analyzers are available for special applications. In general, network analyzers may be separated into two types, namely scalar and vector instruments. As the names imply, a scalar network analyzer will only measure the magnitudes of the S-parameters of the device being tested, whereas a vector instrument can measure both magnitude and phase. In design and development laboratories it is usually necessary to have a vector network analyzer (VNA), since both magnitude and phase information is necessary for most design tasks. In order to make precise high-frequency measurements using a VNA, it is necessary to use a calibration procedure to eliminate systematic errors, and the chapter will ...