AR 10012510, Руководство по эксплуатации и обслуживанию

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Rev D 5
2. THEORY OF OPERATION
2.1 DESIGN OF THE AMPLIFIER
The Model 200T8G18A/250T8G18 TWT amplifier consists of four principal subsystems. Two of these
subsystems, the microwave power assembly (A24380-040 for Model 200T8G18A, A24380-042 for Model
250T8G18) and the TWT power supply (A22520-062) are discussed in sections 2.2 and 2.3, respectively.
The other two subsystems are the microprocessor control system and the TWTA packaging. These both
consist of a number of subassemblies. See the build tree in section 5.1 for further information about how the
parts lists are structured.
The heart of the microprocessor control system is the control head assembly (A26946-300) and the HPA
display board (A22700-900). The microprocessor control system supervises the power supply, provides
metering display, processes operator front panel input, and enables communication with a host computer over
the IEEE-488 interface.
The control head is provided with its own power supply and, other than thru the IEEE-488 interface bus, is
electrically isolated from the amplifier. Communication with the amplifier is via fiber optic links to the HPA
interface assembly (A25444-000).
The TWTA packaging consists of a cabinet assembly (A24381-040), a cooling system (A24382-000) utilizing
a DC powered backwards curved impeller blower and a DC power supply, and various chassis wiring
components.
2.2 DESCRIPTION OF THE RF CIRCUIT
The TWTA consists of two stages of RF amplification: a solid state preamp assembly with adjustable gain
(E01175-000) and a traveling-wave tube amplifier (E30068-000 for Model 200T8G18A, E08114-000 for
Model 250T8G18).
The type N RF input connector is located on the rear panel. The RF input is fed to the input connector on the
solid state preamp. The solid state preamp's output drives the RF input of the TWT. The RF output of the
TWT is a WRD-750 flange. The output is directed through a straight length of waveguide and a 180º E-plane
bend into a dual -30 dB directional coupler. The output of the coupler is a type WRD-750 flange, which
protrudes through the rear panel to serve as the amplifier’s RF output connector.
The reverse port on the directional coupler is connected to a detector diode, whose output is used for VSWR
protection by the power supply logic board, for VSWR measurement in the leveling loop, and for reverse
power measurement on the HPA interface board. With an optional reverse power sample port on the rear
panel, an additional –10 dB coupler is connected to the reverse port of the system’s dual directional coupler.
The output port of the –10 dB coupler is connected to a detector diode whose output is used on the HPA
interface board to measure reflected power and for VSWR foldback and protection. The coupled port of the –
10 dB coupler is connected to the reverse power sample port on the rear panel.
The forward port output is split by a -3 dB splitter. One output is connected to a detector diode via a pad. The
output of the detector is used on the HPA interface board to measure forward power. The other port of the
splitter is connected to the RF sample port on the rear panel. A pad between the splitter and the port isolates
the forward power measurement from mismatches at the sample port.