Chapter 4 Working Principle - Saluki S3871 Series User Manual

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Chapter 4 Working Principle

The solid-state power amplifier amplifies the input signal power to generate the output signal power, the
power supply module provides the DC voltage required by the S3871 series solid-state power amplifier,
the bias plate provides the bias voltage for the solid-state power amplifier, and the power measurement
unit converts the coupled detection output voltage signal from the solid-state power amplifier into RF
output power displayed in dBms and Watts on the LCD screen of the front panel. The schematic diagram
of the amplifiers is shown in Figure 4-1.
Figure 4-1 Schematic diagram for amplifiers of S3871 series solid-state power amplifiers
The S3871 series solid-state power amplifiers adopt two working modes as shown below:
1. Open-loop working mode
With the Setting Wizard keys on the front panel of the instrument, the working state can be set to "Open
Loop". At this time, microwave signals are input from the RF frequency input end of the amplifier, then
amplified by the amplifier and then output through the main loop of the directional coupler. A part of the
output power is sent to a detector through coupling of a directional coupler, which converts the
microwave signals into a voltage signals for processing, and finally the actual output power value is
displayed on the front panel.
2. Internal amplitude stabilization working mode
With the Setting Wizard keys on the front panel of the instrument, the working state can be set to
"Internal Amplitude Stabilization". At this time, the coupling port of the directional coupler in the output
path sends the output coupling signals to the detector and converts it into detection voltage, which, after
amplification, is sent to the internal amplitude stabilization loop inside the amplifier. The internal
amplitude stabilization mode can improve the flatness of the output power.
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