10.1 Introduction

This chapter is intended to cover the basic principles of measuring microwave networks by using a network analyser. The objectives are to discuss the kind of measurements which can be made and the major components in a network analyser covering the basic block diagram, the elements and the advantages and disadvantages of different hardware approaches. Material on error correction is the subject of another chapter. The fundamental concept of microwave network analysis involves incident, reflected and transmitted waves travelling along a transmission line. It must be appreciated, at the outset, that measurement in terms of impedance, which is the ratio of voltage to current, implies knowledge of the characteristic impedance Z ₀ which describes the mode of propagation in the transmission line. Microwave network analysis is concerned with measuring accurately the incident, reflected and transmitted signals associated with a linear component in a transmission line environment. It is important to appreciate that the same quantities may be defined as different values, for example, return loss, reflection coefficient, VSWR, S ₁₁, impedance and admittance are all ways of describing reflection coefficient, and, similarly, gain, insertion loss, transmission, group delay and insertion phase are all ways of describing transmission coefficient.

It is also necessary to understand the fundamental difference between a network analyser and a spectrum analyser. Network analysers are used to measure components, devices and circuits, but a network analyser is always looking at a known signal in terms of frequency and is described...