TABLE OF CONTENTS Transistor manufacturers publish the two-port S-parameters of their transistors in data sheets, which help to predict their microwave properties. The two-port S-parameters can be found in data sheets or on computer disks, or they can be calculated using a transistor model supplied by the manufacturer. Sometimes, especially for UHF and VHF transistors, the Y-parameters or hybrid parameters are given. Various factors, including production variation, bias point, frequency, packaging, and temperature, can affect the S-parameters of a transistor. This section shows how the S-parameters and other data given in data sheets can be used to evaluate how well a particular transistor will work.
Table 6-1 shows an example of two-port S-parameters as they are presented in the data sheet. The S-parameters of the transistor change over frequency and are usually furnished in a table. This particular transistor is a field effect transistor (FET). Its parameters are given in a common-source circuit configuration, which means that the source of the FET is grounded, the gate is attached to Port 1, and the drain is Port 2, as shown in Figure 6-1. Table 6-1 shows the S-parameters listed as magnitude and phase of S 11, S 21, S 12, and S 22 at discrete frequencies. The S-parameters will vary from part to part due to production variations. The S-parameters listed in the data sheets are usually a statistical mean over many production units.
