AR 10046494, Operating And Service Manual, Page: 42 / 60

Model 60/40S1G18B
22 Rev A
3.2.3 A10, A11, A12, A13 Output Power Amplifier
The output power amp is assembled on thin film substrates. The GaN devices, 90
˚
quad couplers and bias
board are the same as the driver amp. The gain should be about 0.5dB less than the driver amp. It delivers
approximately 15-20 watts of RF power. Active bias circuitry regulates the DC current through RF devices.
3.3 RF AMPLIFIER OPERATION HIGH BAND 6.0-18GHZ (SCHEMATIC
10046186)
The High Band RF amplifier assembly consists of a Pre-Amplifier (Pre-Amp), a Driver Amplifier (Driver
Amp), and two 20-watt amplifiers.
3.3.1 A1A1 Pre-Amp
The RF input signal is fed to the A1 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.
The output of the driver amp is fed to the input of a shaper circuit, which flattens the gain. All circuits are
assembled to thin film substrates.
3.3.2 A1A2 Driver Amp
The Driver Amp is assembled on thin film substrate. 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 3 watts of RF power.
3.3.3 A4 & A5 20-Watt Modules
IC Q4-Q7 are current sense amplifiers with a current limit of approximately 4 amps for each IC. Each IC
monitors the current of the 4 FET’s. If overall current for each IC falls below or exceeds certain current limit,
a fault is displayed on front panel and i10V to preamp A1A1.
A 4-way splitter at the input of the 20-watt module feeds 4 RF paths. All RF circuits are assembled on thin
film substrates. The output of the RF channels are tied to a 4-way combiner. The module has a gain of
approximately 17 dB or greater and delivers approximately 20 watts of RF power.