Keysight Technologies
Achieving Accurate RF and
Microwave Power Measurements for
Satellite Thermal Vacuum Test
Application Note
Introduction
Equipment used in space applications needs to go through stringent environmental tests in order to
prove that it can survive the extreme conditions experienced during launch and while in space. Some
of the key environmental tests include vibration, thermal vacuum, and electromagnetic compatibility.
–– Vibration test is important to ensure that the equipment is able to sustain high impact during
rocket launch.
–– Thermal vacuum test is crucial to confirm the equipment is able to operate under the space
vacuum condition.
–– Electromagnetic compatibility test is required due to densely-packed electronic systems
operating at various frequencies. RF signals radiated from high power equipment (transmitters)
can affect the performance of low power equipment (receivers).
This application note focuses on thermal vacuum (TVAC) test, which is typically the final test to be
conducted, and the most complex and expensive test. Detailed planning of the TVAC test is required,
and normally done six to eighteen months ahead of the test in order to ensure success. TVAC testing
helps to uncover possible problems such as outgassing of equipment that could contaminate the
environment, design flaws due to overheating of materials, and a corona (metal vapor arcing) effect
that can cause problems at low pressure.
This application note compares the commonly-implemented power measurement test setups for
TVAC with a new test method that uses TVAC-qualified LAN power sensors. The paper explains how
this new test method provides a simplified test setup, and more accurate and reliable microwave
power measurements for TVAC testing of satellite equipment.
Table of Contents
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Typical TVAC Test Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
New TVAC Test Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Design and Qualification Process of the Keysight TVAC Power Sensor . . . .
Manufacturing Process Ensures the Highest Quality and Reliability . . . . . .
Key Specifications and Benefits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Monitoring and Controlling the Power Sensor’s Temperature in a
TVAC Chamber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Bulkhead Connectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
More Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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03 | Keysight | Achieving Accurate RF and Microwave Power Measurements for Satellite Thermal Vacuum Test – Application Note
Typical TVAC Test Setup
Figure 1 shows the typical test setup for TVAC test. The whole satellite, or satellite
components or modules are placed inside a TVAC chamber. All electrical connections to
the system under test must include hermetically-sealed connector feedthroughs in order
to maintain the vacuum. In general, all the measurement equipment, including the power
meter and sensors, are located outside of the chamber and connect to the satellite
or components using the sealed feedthroughs via switch matrices or a test interface
subsystem.
Long RF cable runs are often needed to connect the power sensor to the satellite inside
the chamber. This can result in accuracy degradation due to poor SWR and insertion loss
due to the length of the RF cable. Complex calibrations are required to calibrate the path
loss as the RF cable performance changes with temperature.
Typical TVAC test setup
Degraded accuracy
RF power meter and sensor are typically installed outside
the chamber and being routed into the chamber via long
RF cables.
Complex test setup
Complicated calibration
routine
Bulkhead connector
interface
Signal generator
RF switch
matrix
Signal analysis
Test interface
subsystem
Thermal vacuum chamber
Network analysis
Power meters
Satellite or
satellite
components
Sensors
Multiplier
DC power system
Computer
Typivcally 40 to 80 ft.
Figure 1. Typical TVAC test setup with all the measurement equipment located outside the chamber and
connected to the satellite or components via switch matrices or a test interface subsystem
04 | Keysight | Achieving Accurate RF and Microwave Power Measurements for Satellite Thermal Vacuum Test – Application Note
New TVAC Test Setup
With the Keysight Technologies, Inc.
U2049XA LAN power sensor equipped
with option TVA, the TVAC-qualified
sensor can be directly connected to the
satellite inside the TVAC chamber (Figure 2).
The benefits include:
The new TVAC test setup
Reliable solution
TVAC qualified Po/LAN power sensors are connected
directly to the input and output of the satellite inside the
thermal vacuum chamber.
High accuracy
Simplified test setup
Remote monitoring
–– Simplified test setup with less
complex calibration routines
Signal generator
–– The sensor now can be connected
directly to the output of the
RF switch
Signal analysis
device under test within the TVAC
matrix
environment and while testing is
Network analysis
being conducted. This removes
the use of RF cables and the need
to perform the associated complex
Multiplier
calibrations. The power sensor
immediately provides accurate
DC power system
output power measurements,
Computer
without path loss calibration.
–– More reliable and accurate power
measurements
–– By eliminating the long RF cable, the power measurement uncertainties due to
insertion loss, poor SWR performance, and temperature effects of the cable are
removed. The power sensor is fully calibrated and offers warranted accuracy
specifications over a temperature range of 0 to 55 °C. Its internal zero and
calibration function also allow users to perform zero and calibrations-on-the-fly
to improve overall measurement accuracy.
–– Remote monitoring
–– By connecting the LAN power sensor to a shared network via a network switch
or power-over-Ethernet (PoE) hub, the power sensor can be controlled remotely
from any part of the world using a Web browser and the Keysight Technologies,
Inc. BenchVue software.
Bulkhead connector
interface
Test interface
subsystem
Thermal vacuum chamber
Power sensor
Input
Satellite or
satellite
components
Power sensor
Output
40 to 80 ft. typical
Table 1 summarizes the benefits of using the TVAC power sensor compared to a
traditional bench power meter and sensor solution.
Table 1. Comparison of traditional and TVAC test methods
Item
Sensor’s location
Power meter and power sensor
Outside chamber, perhaps 60 ft away from payload
Losses due to cable
(based on a typical TVAC cable)
Input power to sensor
Mismatch uncertainty
Measurement uncertainty at 18 GHz
34 dB at 18 GHz
Measurement speed
Total dynamic range and supported
signal types
–10 to –40 dBm
2.56% (between sensor and long cable, cable SWR 1.25)
4.59% (E4413A-H33 at –25 dBm)
3.72% (8485D-033 at –25 dBm)1
400 readings per second (E4413A-H33)
20 readings per second (8485D-033)
90 dB — CW-only signal (E4413A-H33)
50 dB — CW/modulated signal (8485D-033)
TVAC power sensor
Inside chamber, directly connected to payload input/
output or through some adapters
Minimum losses
+24 to –6 dBm
1.30% (between sensor and source, source SWR 1.12)
4.59% (U2049XA at +9 dBm)
50,000 readings per second
90 dB — CW/modulated signal
1. E4413A-H33 and 8485D-033 are Keysight power sensors widely used in satellite testing, and enable
power measurement up to 33 GHz.
Figure 2. New TVAC test setup with sensors connected directly to the input or output of the satellite for
improved accuracy and simplified test setup
05 | Keysight | Achieving Accurate RF and Microwave Power Measurements for Satellite Thermal Vacuum Test – Application Note
Design and Qualification Process for the Keysight TVAC Power Sensor
The Keysight U2049XA option TVA (TVAC power sensor) uses low-level materials with
minimum outgassing properties. Under vacuum, different materials have different
outgassing rates and have the capability to contaminate the vacuum chamber. Therefore,
to ensure that all the materials used in U2049XA option TVA are vacuum compatible,
they are matched against the NASA/ESA outgassing database. Items not listed in the
database are subject to material testing in accordance with ECSS-Q-ST-70 02C1 to
ensure any outgassing is within prescribed limits.
The full sensor assembly is also sent for TVAC qualification based on a typical customer
TVAC profile, as shown in Figure 3. The test shown in Figure 3 was carried out over a
duration of 10 days and 8 hours per temperature cycle. Performance tests were carried
out throughout the different hot and cold temperatures to ensure that the sensor
measured accurately over a wide range of temperatures under the vacuum environment,
and that repeated temperature cycling did not degrade performance. In this example, the
sensor was subjected to operation tests ranging from –10 to +60 °C and non-operating
storage tests from –40 to 100 °C.
TVAC qualification tests are performed in addition to Keysight’s standard environmental
qualification program, known as ETM (environmental test manual). The Keysight ETM
is a collection of test methods and best practices that Keysight uses to ensure that its
product meets applicable regulatory requirements, client expectations, and Keysight’s
published environmental specifications for storage, transportation, and use.
Off
On
Off
Unit on cycles
100 + 0/–3 °C
60 + 0/–3 °C
23 + 0/–2 °C
–10 + 3/–0 °C
–40 + 0/–3 °C
Note: Dwell times are £ 40 mins
Figure 3. Keysight TVAC qualification test profile for U2049XA option TVA
1. Thermal vacuum outgassing test for the screening of space materials by European Cooperation for
Space Standardization.
06 | Keysight | Achieving Accurate RF and Microwave Power Measurements for Satellite Thermal Vacuum Test – Application Note
Manufacturing Process to Ensure Highest Quality and Reliability
Every TVAC power sensor manufactured by Keysight is subjected to thermal vacuum
‘bake out’ in Keysight’s in-house TVAC test facility located in the United States. Each
batch of power sensors is placed inside a TVAC chamber and baked at the pressure
of < 5 x 10 -6 Torr and a temperature of 85 °C for a duration of at least 8.5 hours.
Immediately after the completion of TVAC bake out, the sensors are packed in vacuum
sealed bags to minimize re-absorption of moisture. This process ensures that the sensors
are contaminant-free and ready to use in a TVAC chamber.
Key Specifications and Benefits
Table 2 summarizes the key features and specifications of the TVAC power sensor that
make it ideal for satellite thermal vacuum tests.
Table 2. TVAC power sensor use benefits
Key features and specifications1
Benefits
Wide frequency coverage of 10 MHz to 33 GHz
–– A single sensor that can cover a wide range of satellite bands
Wide power range of –70 to +20 dBm
–– Ability to measure both output signals and small reflected signals
Power over Ethernet (PoE)
–– Enables remote monitoring and control of power measurements over Ethernet with the use of
a standard Web browser and the Keysight BenchVue power meter software.
–– Additional DC power wiring is unnecessary
Internal zero and calibration
–– Performs zero and calibration-on-the-fly at any point of the TVAC test, without having access
to the sensor inside the TVAC chamber
TVAC-qualified
–– Improves overall accuracy with sensor connected to the DUT output directly inside the TVAC
chamber
–– Provides greater confidence in power measurement results
1. For more detailed specifications, please refer to U2040 X-Series data sheet, literature number
5992-0040EN, on www.keysight.com.
07 | Keysight | Achieving Accurate RF and Microwave Power Measurements for Satellite Thermal Vacuum Test – Application Note
Monitoring and Controlling the Power Sensor’s Temperature in a TVAC Chamber
In general, the temperature range for thermal vacuum test can be anywhere from
–196 to +140 °C. It can easily be beyond the operational temperature range of the TVAC
power sensor. Therefore, it is a good practice to monitor the temperature of the sensor
inside the chamber to ensure that it is operating within its supported temperature range.
In common with any powered equipment within a TVAC chamber, the power sensor will
generate heat that can only be removed by radiation or conduction.
Each Keysight TVAC power sensor is shipped together with thermal interface material
(TIM) and two C-brackets. Keysight recommends attaching the sensor to a metal plate or
similar conductive surface, and sandwiching the TIM between the sensor and the metal
plate. The sensor then should be secured tightly onto the metal plate with the C-brackets
(Figure 4). During operation, monitor the temperature of the sensor’s exterior surface
with a thermocouple to ensure it is within its operating temperature of 0 to +55 °C.
When operating the sensor in a cold environment, below 0°C, wrap the sensor with
heat reflective material. This allows its self-generated heat to keep it in the operating
temperature range. When operating in a hot environment, beyond +55 °C, the sensor
needs to be cooled.
Alternatively, turn off the power sensor when operating beyond its operating temperature
range. The non-operating temperature range of the sensor is –40 to +100 °C.
C-bracket
TIM
Figure 4. A thermal interface material (TIM) and two sets of C-brackets are supplied
with every TVAC power sensor (U2049XA option TVA only) for thermal control purposes.
(Refer to U2040 X-Series User’s Guide for mounting dimensions and instructions)
08 | Keysight | Achieving Accurate RF and Microwave Power Measurements for Satellite Thermal Vacuum Test – Application Note
Bulkhead Connectors
A custom-made bulkhead connector is needed to connect the TVAC power sensor
(with PoE interface) inside the chamber to the external computer or PoE switch. Figure 5
shown an example of a sample bulkhead cable adapter (D-sub 50 to Cat5 cable adapter)
that Keysight uses in TVAC qualification tests.
A few manufacturers provide custom-made cable adapter service such as:
–– Airbus Defense and Space Test Laboratories. http://airbusdefenceandspace.com/
–– Pave Technologies Co. www.pavetechnologyco.com
–– Douglas Electrical Components. www.douglaselectrical.com
D-sub 50 pins
connector
TVAC safe
LAN cable
CAT5 connectors
(connect to sensor
inside chamber or
connect to
computer/PoE
switch outside of
chamber
Figure 5. Example of a six-sensor bulkhead cable adapter connected to the sensor inside a TVAC chamber to a computer or PoE switch
located outside the chamber. Connects through a standard hermetically-sealed, 50-way D-sub connector on the bulkhead
09 | Keysight | Achieving Accurate RF and Microwave Power Measurements for Satellite Thermal Vacuum Test – Application Note
Conclusion
The Keysight Technologies U2049XA Option TVA TVAC power sensor is the ideal solution
for satellite thermal vacuum testing inside a TVAC chamber. The TVAC power sensor
comes with numerous benefits. It enables accurate and reliable power measurements
inside a TVAC chamber, simplifies measurement setup, and is suitable for any signal
format. It also offers 100 times faster measurement speed and comes with a wide 90 dB
dynamic range.
Careful considerations have been given to the thermal control of the sensor operating
inside a chamber. Follow the sensor’s mounting instruction for the most effective heat
dissipation in a vacuum environment.
More Information
Keysight U2040 X-Series Wide Dynamic Range Power Sensors data sheet, literature
number 5992-0040EN
Keysight U2040 X-Series Wide Dynamic Range Power Sensors User’s Guide, document
number U2041-90002.
10 | Keysight | Achieving Accurate RF and Microwave Power Measurements for Satellite Thermal Vacuum Test – Application Note
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© Keysight Technologies, 2015
Published in USA, October 21, 2015
5992-1151EN
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