RF Electronics Chapter 9: Impedance Matching of Power Amplifiers Page 334
2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0.
Figure 9.50. Stability of the transformer matched power amplifier, 0.8 -1.2 GHz.
Figure 9.50 shows the input and output stability circles for the 800 MHz to 1200 MHz
frequency range. It can be seen that the amplifier is stable over this entire range, provided
the input source impedance and output load have a VSWR less than 6:1. Figure 9.51
shows the corresponding amplifier frequency response at an input power level of 20 dBm.
It shows that a good S11, good gain and flat frequency response is obtained.
Figure 9.51. Frequency response of the transformer matched power amplifier.
Figure 9.52 shows the input and output stability circles for the amplifier over the 10 MHz
to 2 GHz frequency range. It can be seen that the amplifier is borderline unstable below
100 MHz. To improve the stability, suitable filtering and frequency selective resistive
loading needs to be included in either or both the input and output matching networks.
RF Electronics: Design and Simulation
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