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RF Electronics Chapter 9: Impedance Matching of Power Amplifiers Page 324 2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0. Figure 9.32. Final broadband match S 11 and S 22 on a Smith chart. Figure 9.32 shows that |S 11 | is now less than -20 dB for virtually the entire 250 – 500 MHz frequency range. The curve for |S 11 | is identical to that for |S 22 |. Figure 9.32 shows of S 11 of the network plotted on a close up of the centre of the Smith chart. It can be seen that a good match over the entire 250 to 500 MHz bandwidth is obtained, with the magnitude of the reflection coefficient being less than 0.14 and the VSWR being less than 1.3 from 250 to 500 MHz. A better match can be obtained by using more Pi sections. At frequencies above 100 MHz it is advantageous to replace the inductors in the Pi section with transmission lines. Similar optimisation techniques as described above can be applied to those networks. For impedance matching of the output of transistors or FET's, it is desirable to make the first section a lowpass T network, to reduce harmonic currents and thus increase the amplifier's efficiency. In addition, a bandpass T or L section provides the DC isolation required for biasing. By selecting a suitable Q for one or more lowpass Pi sections, sufficient harmonic filtering of the output can be achieved. Suitable matching networks are thus an essential part of an amplifier design. Example 9.2: Broadband Amplifier Using S Parameters This example uses S parameters and broadband complex conjugate matching, to produce an amplifier. Applying broadband matching to a transistor or FET results in additional problems. Since the device is not normally unilateral, there is an interaction between the input and output matching. As an example consider the MRFE6VS25N LDMOSFET that we used in example 9.1. From the manufacturer's data sheet, the S parameters at a drain current of 2 Amp is shown in table 9.1, where the lines beginning with '!' are comments. The line: '# hz S ma R 6.8', indicates that the frequency in the following file is in Hz, it is an S parameter file and the values are magnitude and phase in degrees, and that the reference impedance is 6.5 Ω. RF Electronics: Design and Simulation 324 www.cadence.com/go/awr