RF Electronics Chapter 9: Impedance Matching of Power Amplifiers Page 329
2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0.
The resulting element modification constants are shown in figure 9.40. S
11
and S
22
are
now only -5 dB and the amplifier gain between ports 1 and 2 is much higher than expected
and oscillations are likely at 165 MH, 302 MHz and 395 MHz. Plotting the stability
circles, shows a very unstable amplifier. K is less than 1 and B1 is negative between 260
and 300 MHz. The amplifier is thus unstable.
Figure 9.39. Broadband amplifier end of step 2.
Figure 9.40. Element modification constants for figure 9.39.
Figure 9.41. Final amplifier performance.
The third step is to make the amplifier stable. The FET input impedance is 4.26 –j17.97 Ω,
corresponding to a Q = 6.1, for the input impedance. Reducing the input Q slightly by
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