Broadband high frequency power amplifier circuit

A broadband high-frequency power amplifier composed of a transmission line transformer and a transistor is shown in the figure.
    Transistors VT1 and VT2 are both 3DG12B. Transmission line transformers are used to transmit high-frequency energy within a wide frequency range and achieve
impedance matching between amplifiers or between amplifiers and loads. Tl, T2 and T3 are broadband transmission line transformers. Tl and T2 are connected in series to form a 16:1 impedance converter to match the
    high output impedance of transistor VT1 with the low input impedance of VT2.
Each stage of the circuit uses a voltage negative feedback circuit to improve the performance of the amplifier.
1. The 8kfl and 47fl resistors are connected in series to provide feedback to the VT1 amplifier, and the 1.2ktl and 12n resistors are connected in series to provide feedback to the VT2 amplifier
. In order to avoid parasitic coupling between amplifier stages through the internal resistance of the power supply, an RC decoupling filter circuit is used. The filter capacitor is
composed of three capacitors of different sizes and materials connected in parallel, which filter different frequencies respectively. Since no tuning loop is used, this amplifier should
work in a Class A state.
    The operating frequency range of the circuit is 2~30MHz, and the output power is 60W. The load is 50fl, 4: l impedance conversion is performed through T3, and
the collector load of VT2 is 200fl. Because it works in a high-power state, its input resistance is about 12fl, and changes with the size of the input signal. In order to
reduce the impact of input impedance changes on the preamplifier, a 12fl resistor is connected in parallel to the input end of VT2, so that the total The input resistance becomes
6tl, and after 16:1 impedance transformation, the electrode load of VT1 is 96fl.