This is the result of a co-founded activity
between RDLabs srl and IMT srl
The
S-Band Transceiver (SBTRcvr)
for microsat platform performs the typical on board telemetry and command
functions. It is composed of two different functional sections, receiver and
transmitter, and it is based onto a well consolidated analogue architecture.
Three trays, or module, stacked in vertical direction
house the unit electronics:
The
receiver function, based on a super
heterodyne architecture, performs the carrier coherent demodulation and provides
as output the command subcarrier video signal. The receiver chain has a double
frequency conversion configuration with first intermediate frequency at about
350 MHz and the second IF at 45 MHz. A crystal filter at second IF implements a
good spurious signal capability and filters the signal to the coherent
demodulation and provides as output the command subcarrier video signal. The
receiver chain has a double frequency conversion configuration with first
intermediate frequency at about 350 MHz and the second IF at 45 MHz. A crystal
filter at second IF implements a good spurious rejection capability and filters
the signal to the coherent demodulator. The I/Q coherent demodulator circuitry
generates amplitude and phase baseband signal respectively used to close the AGC
loop and provide the signal strength telemetry and to close the phase loop.
Demodulated command video signal is routed to the interface circuitry from the
phase branch. Local oscillator signals are generated using a standard PLL
circuit based onto a COTS integrated
synthesizer.
The
transmitter has a very simple
architecture. A crystal oscillator is the reference signal for the PLL circuit
which, based on the standard configuration used in the receiver side, generates
the unmodulated down link signal in the standard frequency range 2200-2300 MHz.
The following modulation circuitry performs the baseband data stream digital
modulation in BPSK or optionally QPSK format and the modulated signal is finally
routed to the power amplifier. Output power levels from 1 watt up to 5 watt are
available as manufacturing options.
SBTRcvr
Block Diagram
The
interface tray houses simply circuitry to buffer the equipment analog and
digital telemetries and DC voltage regulators. A standard DC/DC converter can be
integrated if direct interface with primary bus is required. Standard
configuration requires secondary voltages from the mini/micro sat bus.
The
receiver shows a good sensitivity, it allows the carrier acquisition and
tracking down to –105 dBm while the command demodulation is guaranteed down to
–100 dBm. A rather large tracking range (~500 kHz) is obtained which
significantly simplification of the signal acquisition strategy. Despite the
simple low cost configuration the acquisition and command demodulation
performance are well exceeding typical
in orbit needs.
|
Receiver
frequency |
2050
- 2150 MHz (Custom) |
|
Automati
Frequency Control |
±
150
kHz |
|
Receiver
input signal |
-65
dBm / –105 dBm |
|
Command
subcarrier |
2
kHz, 4 kHz, 8kHz |
|
Command
threshold |
-100
dBm |
|
Command
mod format |
PM/PSK |
|
|
|
Transmitter
frequency |
2250
- 2350 MHz (Custom) |
|
Frequency
stability |
25
ppm |
|
Output
Power |
1
to 5 Watt |
|
Modulation
format |
BPSK
QPSK |
|
|
|
Power
consumption |
(1W
RF) 10 Watt |
|
Weight
|
<1
Kg |
|
S
Band transceiver key performance
In
term of applied technologies the SBTRcvr
is based on robust and standard surface mount device (SMD) manufacturing
approach and high reliable FR4 and Polyammide Printed Circuit Board. The
selection of COTS devices has been made in order to have reduced sensitivity to
radiation. A radiation hardness level of 20 krad has been considered as design
parameter. The modular design allows to derive from the basic design a line of
COTS-based products for LEO missions as transmitter for high data rate
transmission and command receiver for various modulation formats and frequency
bandwidths.
Equipments
S Band Transceiver for MicroSat Platform
