User's Manual Part 1

Table Of Contents
Functiona
l
Description 3EM21522AAAA
DTR-0200-SA-SIRIUS Issue 1, March 2008
2-20
2.4.3
HPA PREAMPLIFIER (PREDRIVER)
The pre-driver is the first amplifying stage of the HPA. It employs three stages of
amplification-a Monolithic Microwave Integrated Circuit (MMIC) amplifier and two
LDMOS transistors. The pre-driver raises the output power of the RF from the up-
converter by 38 dB and feeds the amplified RF into the HPA driver amplifier. The RF
signal from the pre-driver input is also coupled to the RF detector circuit which pro-
vides detected RF to the HPA controller for monitoring and gain control. The coupled
RF signal is routed through a PIN diode attenuator to maintain the HPA gain con-
trol loop. The pre-driver amplifier, via a Gallium Arsenide (GaAs) MMIC RF switch,
can turn the RF signal on or off by way of a logic level HIGH RF Shutdown TTL con-
trol signal.
2.4.4
HPA DRIVER AMPLIFIER
The driver amplifier, employing two parallel amplifiers, receives the RF output from
the pre-driver and amplifies it by 13.3 dB. The output of the driver amplifier is fed
into a five-way splitter at a power level of 43 dBm.
2.4.5
HPA POWER SPLITTER
The five-way power splitter is connects directly to the HPA driver amplifier RF out-
put. The splitter evenly distributes this RF power to the five individual output power
amplifier modules.
2.4.6
POWER AMPLIFIER MODULES
The five power amplifier modules are identical to the driver amplifier module. These
modules are paralleled and receive equal inputs from the five-way power splitter.
The amplifiers each contribute a gain of 13.3 dB to their respective input, the five-
way combiner/coupler.
2.4.7
COMBINER/COUPLER
The five RF power amplifier outputs are combined into one via a zero-degree star
combiner. Two stripline couplers provide output signal sampling. One coupler’s out-
puts are terminated with SMA connectors and are used to provide external forward
and reflected RF monitoring ports. The other coupler’s outputs are detected using
true-type RF detectors installed on a coupler printed circuit board. These detected
signals are fed to the HPA Controller for control and monitoring purposes. The
detected signals and DC power for the on-board detectors are routed through 6-pin
Molex connectors installed on a coupler board. The 5-way combiner/coupler requires
external +5VDC ± 0.5 volts. When the combiner/coupler is installed on the HPA chas-
sis, the inputs are connected directly to the power modules’ output pins. The output
of the combiner is connected to the central conductor of the HPA output connector.