AR 10046494, Operating And Service Manual, Page: 41 / 60

Rev A 21
3. THEORY OF OPERATION
3.1 INTRODUCTION
The Model 60/40S1G18B RF amplifier consists of a 0.7–6.0 GHz RF amplifier assembly and a 6.0 to 18 GHz
amplifier assembly.
The power supply section consists of an AC input filter, a switch, three switching power supplies, 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 – LOW BAND 0.7-6.0 GHZ (SCHEMATIC
10046186)
The Low Band RF amplifier assembly consists of a Pre-Amplifier (Pre-Amp), a Quad Amp (Driver Amplifier
A8) and four Output Amplifiers (A10, A11, A12 and A13).
3.2.1 A7 Pre-Amp
The Pre-Amp is assembled on thin film substrates. The RF input signal is fed to the A7 Pre-Amp. The pre-
amp consists of a GaAs Attenuator, MMICs and a Wilkinson splitter. The 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 A7
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 driver is fed to another MMIC to boost the gain. Total gain is about 30dB.
3.2.2 A8 Driver Amp
The Driver Amp is assembled on thin film substrates. It has two (2) GaN amplifier sections. Each section is
input and output DC isolated by coupling capacitors. A 90
˚
quad coupler combines the RF outp uts. 50Ω
termination resistors absorb any difference signals and help to improve the input and output VSWR of the
module. The module has a gain of approximately 10dB and delivers 6 watts of RF power. Active bias
circuitry regulates the DC current through RF devices.