Overview

From APPLIED MICROWAVE & WIRELESS, VOL. 7, NO. 4, FALL 1995

Modern DAE techniques combined with component modeling and sound engineering judgment have changed linear RF amplifier design from an art to a science. When reliable S-parameters are available for the active device the initial RF design procedure is reduced to one of three procedures based on the transducer power gain, available power gain, or operating power gain definitions. The first of these techniques is outlined below; the other two will be discussed in a future article.

Transducer Gain Approach

Of the many existing gain definitions the transducer power gain [1] of a two-port network (shown in Figure 1) is defined as

Figure 1: Generalized block diagram of a two-port device connected to arbitrary source and load terminations. The two-port device is characterized by its basic Z ₀-based S-parameters.

Since the components of this basic definition are difficult to interpret, generally one of two alternative forms is used:

where

or

where

? _IN and ? _OUT represent the true input and output reflection coefficients of the two-port, having any arbitrary terminations ? _S and ? _L. Viewing these expressions gives a better interpretation of the composition of the overall gain since there are three distinct portions related to gain. These are:

1. G ₀: the basic 50-ohm gain, S ₂₁

2. G