ETTC'2003 - SEE

3.5 ACPR RACK
Gateway and satellite power amplifiers are
part of the major contributors in term of
signal degradation as it is necessary to
adjust their operating points very close to
saturation to maximise the RF output
power. In order to represent these nonlinear
effects, equipment called ACPR
(Adjacent Channel Power Ratio) Racks
have been developed by CNES. These
racks allow the selection of operating
points for the power amplifiers
corresponding to a wanted value of the
ACPR, this criteria being commonly used
to characterise power amplifier effect on
signal quality. The ACPR level is
determined by computing the ratio
between the power in the useful frequency
band (B on the figure) and the power in the
upper (C on the figure) and the lower (A
on the figure) frequency bands. In the scope of our developments we have designed and developed 2
specific ACPR racks, in C and Ka band, allowing to set and control on each rack the ACPR level of up to
3 different channels in a range of 15 dBc to 40 dBc.
3.6 TWTA AMPLIFIER RACK
-24.5
-30
-35
-40
1AVG
-45
-50
-55
-60
-65
-70
-74.5
Ref Lvl
-24.5 dBm
Gain (dB)
68.0
67.0
66.0
65.0
64.0
63.0
62.0
61.0
60.0
59.0
RBW 3 MHz
VBW 10 MHz
SWT 5 ms
-35.0 -32.5 -30.0 -27.5 -25.0 -22.5 -20.0 -17.5 -15.0 -12.5 -10.0
Pe (dBm )
Mag_18.5G Hz Mag_19GHz Mag_19.5G Hz
The satellite power amplifier is one of the major element of the transmission
chain as it allows delivering the power to solve the link budget between the
satellite and the Earth. However, as it is mentioned above, this component can
introduce degradations on the useful signal. The goal of the technology is then
to develop high power on-board Travelling Wave Tube Amplifiers (TWTA) in
Ka-band with a high level of efficiency (transfer of DC power into RF power)
combined with good linearity.
For the BST, in order to characterise the behaviour of the TWTA in its operational conditions and the
associated degradation on the useful signal, we have integrated a TWTA flying model in Ka band (power
at saturation 80 W, efficiency 60 %) coming from CNES R&D. This rack includes an ALC (Automatic
Level Control) driven by a proprietary software in order to control the Input Back Off (IBO) of the
TWTA with a ± 0.1 dB accuracy.
cl1
Marker 1 [T1]
-40.91 dBm
3.89013828 GHz
C0
cl1
4
RF Att 10 dB
Unit dBm
Center 3.871 GHz 15 MHz/
Span 150 MHz
Date: 14.FEB.2003 11:15:10
A B C
1
C0
cu1
1 [T1] -40.91 dBm
3.89013828 GHz
CH PWR -16.55 dBm
ACP Up -25.02 dB
ACP Low -23.90 dB
cu1
A
1RM