User's Manual

Chapter 2 System Description
2.3.15.5 High Power Amplifier (HPA)
T
he HPA operates as the final amplification stage for the terrestrial repeater. It utilizes
highly efficient, LDMOS transistor technology to amplify the S-band terrestrial signal from
the exciter to a power level of 400W (56 dBm). This solid-state design operates in a
Doherty configuration over a frequency range of 2320 MHz to 2345 MHz.
The HPA sub-system employs eight (8), air-cooled HPA’s, which are power/phase combined
to provide an sub-system output power level of 1.74 kW (62.4 dBm) post filter. Each HPA is
powered by an individual 30 VDC rectifier module, which is external to the HPA.
The HPA contains a pre-driver, a driver, a 4-way splitter, four individual power amplifier
modules, a 4-way combiner/coupler with RF detector and an HPA controller. The four power
modules operate in a parallel configuration, allowing the HPA to operate in soft fail mode.
Under normal conditions, the HPA can operate with a maximum output power level of 56 dBm
(400W). In the event of a single power module failure, the HPA is capable of operating at a
reduced output power level of 53 dBm (200W). With the failure of a second power module,
the HPA is capable of operating at a reduced output power level of 50 dBm (100W).
The HPA incorporates an internal ALC loop to maintain a constant output power level.
Forward power detection is performed at the output of the HPA’s internal 4-way
combiner/coupler by RF detector circuitry. The HPA also includes an adaptive pre-corrector,
which effectively pre-distorts the input drive signal to minimize amplifier distortion and reduce
spectral regrowth.
The HPA is fully protected against input overdrive, output load VSWR and temperature faults.
The protection circuits are all self-correcting, allowing restoration of the HPA to its normal
operational state upon removal of the fault condition.
The HPA controller is used for monitoring and control of all HPA parameters and provides
protection against abnormal operating conditions. In a DRU-2KW, each HPA is connected to
the TSC via a RS-485 serial bus. The TSC is connected directly to the exciter via a RS-422
serial interface for monitoring and control of the eight (8) HPA’s.
Figure 2-31 HPA
SX03-30000-01-M01
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