AR 20S6G18-L, Operating And Service Manual, Page: 35 / 50

Rev E 19
3. THEORY OF OPERATION
3.1 INTRODUCTION
The Model 40S6G18-L RF amplifier consists of a 6.0–18 GHz RF amplifier assembly. The RF amplifier
assembly consists of a Pre-Amplifier (Pre-Amp), a Driver Amplifier (Driver Amp), 2 way splitter, two 20-
watt output modules and a 2-way combiner.
The power supply section consists of an AC input filter with a circuit breaker switch, a switching power
supply, and a regulator circuit.
The control system consists of a Control/Fault Board, an Interface Board and remote interfaces for IEEE-488,
RS-232, USB, and Ethernet.
3.2 RF AMPLIFIER OPERATION
3.2.1 A1A1 Pre-Amp
The RF input signal is fed to the A1A1 Pre-Amp, RF attenuator U1. U1 is a Gallium Arsenide (GaAs) Field-
Effect Transistor (FET) Attenuator. DC signals between approximately -0.5 V to -2.5 V are used to control
the shunt and series legs of the RF Attenuator. This Attenuator is used for manual gain control using the front
panel gain control and to attenuate RF input signals above 0 dBm by utilizing internal voltages.
U2 is a broadband GaAs Monolithic Microwave Integrated Circuit (MMIC) and is the first stage of gain in the
amplifier. The output of U2 is fed to the input of the Wilkinson Two-Way Splitter.
The Wilkinson Two-Way Splitter splits the signal into two paths. One output is fed to the input of the A1A2
Driver Amp and the other output is fed to a detector. The detector output is used to protect the unit in the
event of input overdrive.
3.2.2 A1A15 Shaper
The function of the A1A15 shaper is to flatten the gain.
3.2.3 A1A2 Driver Amp
The Driver Amp is assembled on thin film substrates. It has one GaN MMIC FET gain stage. The stage is
input and output DC isolated by blocking capacitors. The module has a gain of approximately 18 dB and
delivers approximately 6 watts of RF power.
The output of the driver amp is fed to the input of a shaper circuit, which flattens the gain.