Introduction

In Chapter 1 we introduced and classified models according to the mathematical structure of the model. However, several other properties and classifications of PA behavioural models are possible that are not directly related to the model itself. They are a result of the observed PA characteristics, which are reflected by the model.

Here we will highlight aspects and properties of behavioural models and will also discuss important issues concerning the characterisation of microwave amplifiers. The model properties and classifications used in this context can be divided into the following major groups:

• properties derived from the model structure;

• properties introduced by the PA modelling application;

• properties reflecting the behaviour of the observed amplifier under a specific excitation.

The most important of these properties are summarised in Figure 2.1.

Obviously, a model can represent several of these characteristics simultaneously. Some properties listed in the figure describe the same model characteristic from different points of view. For example, one may classify models according to the presence of linear or nonlinear memory effects using the structure presented in Figure 1.6, whereas another possibility is to assume a specific structure for the observed amplifier and then divide the dynamic nonlinear behaviour into shortand long-term memory effects.

In Section 2.2, model- and model-structure-based properties of behavioural models are summarised for completeness. Most of these properties and classifications were introduced in Chapter 1.

In Section 2.3 we briefly present the differences between models classified as circuit-level and system-level.