Payload Telecomunicazioni Satellitari - per
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Payload
per
Telecomunicazioni Satellitari
Ernesto Limiti Sistemi Elettronici per lo Spazio – A.A. 2019/2020
SEGNALI DI UP-LINK E DOWN-LINK
Tipicamente un satellite è un trasponditore che ha il semplice compito di captare
da Terra un segnale debole, amplificarlo mediante un amplificatore a basso
rumore, cambiare la frequenza del segnale così ottenuto dalla frequenza di UP–
LINK a quella di DOWN–LINK, amplificare nuovamente il segnale e, infine,
ritrasmettere il segnale a Terra (Payload trasparente).
I satelliti di ultima generazione prima di portare il segnale alla frequenza di
DOWN–LINK lo trasferiscono in banda base e lo rigenerano (Payload rigenerativo).
Space Segment
uplink downlink Ground Segment
TT&C
Ernesto Limiti Sistemi Elettronici per lo Spazio – A.A. 2019/2020
Telecom Satellites : Frequency Allocations
Satellite communication services have frequency allocations that are different for
transmission from ground to the satellite (uplink) and for transmission from the
satellite to ground (downlink). Frequency allocations historically used are :
C Band : 5.7 ÷ 6.2 GHz uplink, 3.7 ÷ 4.2 GHz downlink
X Band : 7.9 ÷ 8.4 GHz uplink, 7.25 ÷ 7.75 GHz downlink
Ku Band: 12.75 ÷ 14.70 GHz uplink, 10.90 ÷ 12.75 GHz downlink
17.2 ÷ 18.2 GHz uplink, 11.75 ÷ 12.75 GHz downlink
Ka Band: 27.5 ÷ 31.5 GHz uplink, 17.5 ÷ 21.5 GHz downlink
Single channels exhibit a bandwidth of 27 ÷ 54 MHz, typically grouped to form an
overall bandwidth of 500 MHz for each of the two polarisations (horizontal and
vertical or circularly polarised) of the antenna.
Ernesto Limiti Sistemi Elettronici per lo Spazio – A.A. 2019/2020
Transparent Payload Scheme
DOWNCONVERTER IMUX CAMP/LINRZs TWTAs OMUX ANTENNA
ANTENNA
1 1
LNA
2
LOCAL OSCILLATOR
N
N = 24 .. 44 TYP
M = 4 .. 8 TYP
REDUNDANCY REDUNDANCY
SWITCHES SWITCHES
Ernesto Limiti Sistemi Elettronici per lo Spazio – A.A. 2019/2020
Input Filters
The entire Uplink signal is separated by
potentially interfering frequencies (in
particular from the transmitted ones,
the downlink) by highly selectve filters,
realised in WG (full uplink band)
Typical features
Input Frequency
C/X-Band: 5.6-8 GHz (WR137)
Ku-Band: 13-14.5 GHz (WR75-62)
Function Bandpass/Bandstop
Topology Rectangular Waveguide
Very Low Loss Behavior: 0.2dB @ 2 %BW (Ku)
High Q-factor 14000 (X); 6000 (Ku)
Spurious response free >50dBc up to 19Ghz
Mass 150-200 gr.
Ernesto Limiti Sistemi Elettronici per lo Spazio – A.A. 2019/2020
Communication Receiver (1)
Functions grouped in the communication receiver (to be distinguished by the command receiver)
are:
• Low-Noise amplification at the uplink frequency
• Frequency conversion via mixing with a local oscillator, internally generated
• Downlink amplification
Such functions are realised via a set of microwave integrated circuits realised in Hybrid or
Monolithic form, using solid-state devices for any active function.
RF HYBRID MODULE
LNA
MIXER
RF IN IF OUT
IMG FILT IF FILTER
2-3 GHz SPLL
SLOPE COMP
DIGITAL TEMP GAIN COMP
COMPENSATION
SECONDARY VOLTAGES
LO MODULE
DC/DC MODULE
POWER BUS TLM/CMD
Ernesto Limiti Sistemi Elettronici per lo Spazio – A.A. 2019/2020
Communication Receiver (2)
Different receivers are selected for reliability reasons through redundancy switches
30/20 GHz Low Noise converter
Dual Redundant 30 GHz LNA
Ernesto Limiti Sistemi Elettronici per lo Spazio – A.A. 2019/2020
Communication Receiver (3) – Sample Ka Band LNA
Technologies
Typical performance
Input frequency 27.5 - 31.5 GHz Hybrid MIC packaging
Noise Figure 2.3 dB (1.9 dB at 25°C) Thin film for MICs
Gain 37 dB typ
Output Int. Point + 23 dBm PHEMT process for MMICs
Power Consumption 1.5 Watt
Mass 100 grams single LNA without DC/DC
Ernesto Limiti Sistemi Elettronici per lo Spazio – A.A. 2019/2020
Communication Receiver (4) – Sample Ku Band LNA-Downconverter
Typical Performance
Input Frequency 12.7 - 14.7 GHz
Output Frequency 10.7 - 12.7 GHz
Noise Figure 1.8 dB (receiver)
Gain 55 dB typ, receiver
26 dB typ, conv.
Output Intercept Point +29.5 dBm
Frequency Stability ± 1 ppm over temp
Power Consumption 7.0 Watt
Mass 500 grams (converter)
Ernesto Limiti Sistemi Elettronici per lo Spazio – A.A. 2019/2020
Communication Receiver (5) – Sample Ku Band LNA-Downconverter Ernesto Limiti Sistemi Elettronici per lo Spazio – A.A. 2019/2020
Communication Receiver (6) – Ku Band LNA Ernesto Limiti Sistemi Elettronici per lo Spazio – A.A. 2019/2020
Communication Receiver (7) – Ku Band LNA Ernesto Limiti Sistemi Elettronici per lo Spazio – A.A. 2019/2020
Communication Receiver (8)
Any communication receiver includes therefore a local oscillator section : it is typically made by a
phase locked loop in which a microwave oscillator (hybrid or monolithic) is locked to a given
harmonic of a reference quartz oscillator, operating at 10-100 MHz.
As in the majority of electronic apparatuses onboard, the primary power from the bus (up to
100V DC) has to be converted to voltages compatible with the electronic circuits of the
microwave and control sections (5-10 V) : a DC/DC converter is realised with an oscillating circuit
(up to 100kHz) with efficiencies over 90% (low power).
Typical resulting performances
Gain 55 dB
Noise Figure 1.8 dB (14 GHz), 3.0 dB (30 GHz)
3rd order intercept 26 dBm per carrier
Frequency stability 1x10-6 (between -10° and 60°C), 4x10-6 EOL (15 years)
Ernesto Limiti Sistemi Elettronici per lo Spazio – A.A. 2019/2020Communication Receiver (9) – LO generation
Local Oscillator
The stability requirement forces the selection of an oscillator with a crystal reference: technology
limits the oscillator reference frequency below 150 MHz.
To get the LO frequency (1-3 GHz Ku receivers, 9-12 GHz Ka receivers) different techniques can be
adopted:
• subsequent multiplications and filtering
• Phase Locked Loop at fundamental frequency
• Sampling Phase Locked Loop
There is not a single solution for any apparatus !
10 GHz
1/128
LOOP
FILTER
LOOP
100 MHz
10 GHz
FILTER
78 MHz
10 GHz SAMPLING PHASE
DETECTOR
Ernesto Limiti Sistemi Elettronici per lo Spazio – A.A. 2019/2020Communication Receiver (10) – Sample osc (Globalstar 2)
Quad-PLLO Each FGU comprises sixteen different microwave
hybrid frequencies, factory-set:
8 prime + 8 redundant ~5 GHz PLLOs
8 prime + 8 redundant ~7 GHz PLLOs
LO signals are locked to one of two DXOs
(Disciplined Xtal Oscillator) @4.845 MHz in cold
redundancy, lockable to GPS pulse per second
signals.
One FGU per satellite is foreseen, i.e. 48 total: at
highest rate, 1 FGU per week is requested.
Technology employed is :
MMIC HBT voltage controlled oscillators;
PLL based on SOI synthesizers
macrohybrid packaging;
Ernesto Limiti Sistemi Elettronici per lo Spazio – A.A. 2019/2020Communication Receiver (11) – Design criteria
Gain partitioning for the RF (before the mixing) and IF (after the mixing) sections is to be
performed as a function of the contrasting requirements of low noise figure and high
linearity.
Using very simple relationships for both
F2 1
F F1
G1
1
IP
1 1
IP2 G2 IP1
lead to the construction of easy-to-use and first-pass performance tables
Ernesto Limiti Sistemi Elettronici per lo Spazio – A.A. 2019/2020Communication Receiver (12) – Design criteria Ernesto Limiti Sistemi Elettronici per lo Spazio – A.A. 2019/2020
Input Multiplexer
After the communication receiver, an input
multiplexer (IMUX) finally split the entire uplink
full band into its channels. This is to recover the
path and atmosphere losses via the subsequent
Channel Amplifier.
Channels are splitted to avoid channel
intermodulation
Ernesto Limiti Sistemi Elettronici per lo Spazio – A.A. 2019/2020Channel Amplifiers & Linearisers (1)
A Channel amplifier has the task to amplify the microwave channel signal using two different
modes:
• Fixed Gain: allowing the selection (from ground commands) of the desired gain (typically 30
dB within 10 ÷ 60 dB)
• Authomatic Level Control (ALC):allowing the selection (from ground commands) of the output
power (typically 15 dB between -20 and +10 dBm)
In the ALC mode, the output level is hold constant by a reaction loop acting on variable
attenuators and compensating input power fluctuations between -60 and -20 dBm.
A[dB]=Ka*Va[V]
Pin[dBm] Pout[dBm]=Pin[dBm] + (G - A) [dB]
Va[V]
Ki Vd [V]=Kd*Pout[dBm]-Vref[V]
F(s)
s
Ernesto Limiti Sistemi Elettronici per lo Spazio – A.A. 2019/2020Channel Amplifiers & Linearisers (2) - Scheme
FLATNESS
CORRECTOR
VGA VGA VGA VGA VGA FILTER VGA VGA
RF IN RF OUT
MICROWAVE
REG. LINES
SECTION
CONTROL
GAIN CTRL OPENLOOP TRIMMING
SECTION
V POS SUPPLY
SERIES
FILTER REG'S
V NEG ALC
VREF
DETECT. VOLT.
VDD
CURVE FIT
v+v- vdd vee
PWR TLM
ALC ON/OFF
TEMP
CURVE FIT
COMP.
DAC FIXED GAIN
GAIN/LEVEL
WORD (8 BITS)
COMMAND AND
SERIAL TELEMETRY
BUS INTERFACE
Ernesto Limiti Sistemi Elettronici per lo Spazio – A.A. 2019/2020Channel Amplifiers & Linearisers (3)
In the case of highly linear operation or multicarrier transmission within the same channel, the
channel amplifier is typically associated with a lineariser, whose task is to pre-distort the input
signal to the subsequent TWTA high power amplifier
C-BAND TWTA
C BAND CHANNEL
AMPLIFIER WITH
LINEARIZER
Ernesto Limiti Sistemi Elettronici per lo Spazio – A.A. 2019/2020Channel Amplifiers & Linearisers (4)
The TWTA exhibits two distortion phenomena:
AM/AM : nonlinear power transfer characteristic as function of the input power
AM/PM : nonlinear variation of the output signal phase characteristic induced by input power
variations
EFFECTS:
• In the multi-carrier case, intermodulation products will be generated; downlink power related to
each carrier frequency will be a function of the channel total power, and if one of the carrier
frequencies will saturate the TWTA will suppress the other ones (will decrease the transmitted
power).
• In the modulated single-carrier case, envelope fluctuations will be converted into a spurious
phase modulation
In the modulated single-carrier case, the TWTA will be operated at saturation to get the maximum
transmitted power (e.g. for modulated FM TV broadcasting). In other single carrier applications, as
for instance in digital transmission with TDM access, it is experimentally demopnstrated theat the
error probability on the link exhibit a minimum for transmitted powers slightly lower than the
maximum (2 dB input backoff). This is because of the distorsion effects that, close to saturation,
have a prevailing effect over the S/N degradation due to thermally generated noise.
In multicarrier applications, as for instance FDM access, hundreds of narrowband modulated
carriers may be simultaneously present: in this case, to get an acceptable C/I, the TWTA will be
operated with a strong input backoff (e.g. 10 dB).
Ernesto Limiti Sistemi Elettronici per lo Spazio – A.A. 2019/2020Channel Amplifiers & Linearisers (5)
20 20
10 10
dBW 0 dBW 0
-10 -10
-20 -20
-30 -30
-40 -40
-50 -50
-60 -60
-70 -70
-80 -80
-70 -50 -30 -10 10 30 50 70 -70 -50 -30 -10 10 30 50 70
-60 -40 -20 0 20 40 60 -60 -40 -20 0 20 40 60
delta f [MHz] delta f [MHz]
fdm spectrum with 10 equal carriers suppression with a saturated carrier
Ernesto Limiti Sistemi Elettronici per lo Spazio – A.A. 2019/2020Channel Amplifiers & Linearisers (6)
Lineariser
The distortion effects can be compensated with a large variety of techniques. The most
adopted onboard is the (RF) pre-distortion one, based on axpanding, with a suitable device,
the signal to be fed into the TWTA, with AM/PM characteristics that are opposite to the
ones presented by teh TWTA.
The basic scheme of a sample predistorteris the following: the input is split into two paths
(90 deg apart), the first operating under strong compression (upper branch in the
following). The other one is fully linear. The two branches, with similar small-signal gains,
are combined out-of-phase at the output, to partially cancel. At the saturation of the non
linear branch, the cancellation will be less and less effective, causing therefore a gain
expansion.
r' a LIN
= a 'LIN
90° coupl 90° coupl
r
a'
NL
f
a NL
Ernesto Limiti Sistemi Elettronici per lo Spazio – A.A. 2019/2020Channel Amplifiers & Linearisers (7)
Main Performance
Operating Frequency C (3.4-4.2)
X (7.2-8.4)
Ku(10.7-12.7)
Ka (17.7-21.2)
Bandwidth 500 MHz typical
Operating Modes ALC and Fixed Gain
Output Level -14 to +6 dBm in 0.5 dB
steps
Gain Control Range 10 to 60 dB
Setpoint Control 3.5 dB typical
LCTWTA NPR 17.5 dB at 3 dB OBO
Power Consumption 3.3 Watt @ ±6.5V
Mass 250 grams
Ernesto Limiti Sistemi Elettronici per lo Spazio – A.A. 2019/2020Travelling Wave Tube Amplifiers Ernesto Limiti Sistemi Elettronici per lo Spazio – A.A. 2019/2020
Output Multiplexers Ernesto Limiti Sistemi Elettronici per lo Spazio – A.A. 2019/2020
Regenerative Payloads (1)
In recent systems, in multimedia services
(satellite internet and in general services
that are characterised by interactive and
high data rate features), the regenerative
architecture is adopted.
In this case the payload receives the
signals, demodulate them in BB, process,
and re-transmit to ground.
Examples of application include the
downlink routing of signal towards the
desired beam or grouping more than one
uplink beams (from different content
providers) in a single downlink (e.g. for
digital TV broadcasting)
Ernesto Limiti Sistemi Elettronici per lo Spazio – A.A. 2019/2020Regenerative Payloads (2) – Simple Scheme
IMUX TWTAs OMUX ANTENNA
ANTENNA
1 1 1 1
DEM MOD
BASEBAND
2
PROCESSING
M
LNAS N
DOWNCONVERTERS
P P
Ernesto Limiti Sistemi Elettronici per lo Spazio – A.A. 2019/2020Regenerative Payloads (3) – Different Scheme
LNA assy DC/DC Converter
RF EPC
OBMM output
Branching
TO ANTENNA FARM
filter
ANTENNA FARM
TWTA Output red. matrix
TWTA Intput red. matrix
Channel
Filter
8/6 coaxRed. matrix
coaxRed. matrix
EPC
EPC
OBMM inputred.matrixandbranching OBMM outputred.matrixandbranching
Antenna Pointing
System (if needed)
Synth.
Synth.
Synth.
Synth.
IF IN IF OUT IF IN IF OUT IF IN IF OUT IF IN IF OUT
(33 MHz ch.)
(33 MHz ch.)
(33 MHz ch.)
(33 MHz ch.)
CPRU
CPRU
CPRU
CPRU
UHF
IF Interface
DATA I/O
Interface
SoF
int. Red. Switch Fabric and Controller (OCMX)
Ernesto Limiti Sistemi Elettronici per lo Spazio – A.A. 2019/2020Regenerative Payloads (4) – Sample Ku/IF/BB downconverter chain
BB Out
Typical Performance
RF Input
RF Input Frequency 10/13 GHz
Output Frequency 10/400 MHz
Maximum Gain 90 dB
Gain Control Range 45 dB
OIP3 20 dBm
Noise Figure 16 dB
1st IF Out Image Rejection 25 dB
LO Input DC Power Cons. 2.5 Watt
Mass Properties 150 gr
Ernesto Limiti Sistemi Elettronici per lo Spazio – A.A. 2019/2020TT&C Subsystem – a Vital system Ernesto Limiti Sistemi Elettronici per lo Spazio – A.A. 2019/2020
TT&C Subsystem – Ku Band Command Receiver
Typical Performance
Receiver Frequency 13/17GHz (Dual Freq. Opt)
Rec. In.Level Range -50/-112 dBm
Modulation FM dev. ± 400 kHz
Digital Demod. Opt. BPSK, FSK
Squelch Thr below -115 dBm
Receiver Selectivity 50 dB @ ± 2 MHz
Cmd SNR 46 dBHz @ -112 dBm
DC Power Cons. 8 Watt
Mass Properties 1.2 / 1.4 Kg.
Ernesto Limiti Sistemi Elettronici per lo Spazio – A.A. 2019/2020TT&C Subsystem – Ku Band High Power Transmitter
Phase +39dBm
Mod.
Φ PLL
VIDEO
I/F
+28dBm
RNG TLM
DC/DC
Typical Performance
Transmitter Frequency 11.5 / 12.75 GHz
Frequency Stability ±4ppm
Output Power Level +39dBm
Extra output +28dBm (Dual Pwr Opt)
Output Phase NoiseYou can also read
