Space EMC and RF: controlling electromagnetic interactions to secure the mission
In the space sector, electromagnetic compatibility and control of RF performance are essential to the correct operation of equipment, subsystems, satellites, launchers and payloads.
A space system brings together a large number of electronic and radio-frequency units in a highly integrated environment. On-board computers, power supplies, converters, control systems, transmitters, receivers and RF payloads must all be able to operate simultaneously without interfering with one another and without degrading mission performance.
The issues involved cover conducted and radiated emissions and susceptibility as well as transients, electrical interfaces, coupling between units and the performance of RF and microwave chains.
In telecommunications satellites, an additional challenge lies in the coexistence of high-power transmit signals and extremely sensitive receivers. Spurious emissions, harmonics and intermodulation phenomena, in particular PIM (Passive Intermodulation), then become key parameters of system performance.
ECSS standards, supplemented by the requirements of agencies, prime contractors and space programmes, provide the framework for design, qualification and validation activities.
HEMERA RF supports space industry players in defining and integrating EMC, RF and microwave test facilities, from equipment qualification through to the electromagnetic compatibility and RF performance challenges of complex systems.
From component to satellite: several levels of validation
What sets the space sector apart is the need to control electromagnetic interactions at several different levels.
In particular, it is important to distinguish between:
Components and units → subsystems → platform and payload → integrated satellite
Each level raises different issues.
At the level of an electronic unit, the aim is in particular to verify its emissions and its susceptibility to disturbances.
When several units are assembled into a subsystem, their electrical interfaces, cabling, grounding, shielding and electromagnetic interactions also become decisive.
At the level of the complete satellite, the issue becomes a genuine system-level one: all units must be able to operate simultaneously without any conducted or radiated emission, harmonic, spurious signal or unwanted coupling compromising another function.
This approach is particularly important in space, because an anomaly that only appears once the satellite is in operation can be extremely difficult, or even impossible, to correct physically.
EMC must therefore be addressed from the design stage and then verified step by step throughout the integration and qualification phases.
Platform and payload: two complementary functions
To understand the EMC and RF challenges of a satellite, it helps to distinguish between the platform and the payload.
The platform, or bus, groups together the functions needed to operate the satellite: power generation and distribution, thermal control, attitude and orbit control, on-board data handling, telemetry and telecommand, as well as various service functions.
The payload, for its part, performs the mission itself. Depending on the satellite, this may be telecommunications, Earth observation, navigation, meteorology, scientific instrumentation or other specialised missions.
From an electromagnetic point of view, these two assemblies must operate within a limited space while accommodating:
- digital electronics
- power electronics
- converters and power supplies
- on-board computers
- communication buses and interfaces
- RF equipment
- high-power transmitters
- sensitive receivers
- antennas and microwave chains.
Compatibility between the platform, the payload and the RF environment is therefore a major challenge in satellite integration.
ECSS: the European framework for space projects
In the European space sector, the ECSS (European Cooperation for Space Standardization) standards form a major reference framework for the design, development and qualification of space systems.
Rather than relying on a single test standard, EMC requirements form part of a broader engineering process covering the definition of the electromagnetic environment, the requirements applicable to units and subsystems, verification methods and the compatibility of the integrated system.
The applicable standards must always be determined according to the programme, the agency, the prime contractor, the mission and the qualification level concerned.
This logic is important: in space, EMC is not simply a matter of putting a unit through a series of tests at the end of development. It must be built into the electrical and RF architecture of the system from the design stage.
EMC qualification of electronic units and subassemblies
At unit level, testing serves in particular to characterise the disturbances generated and to verify immunity or susceptibility to the environments to which the unit may be exposed.
Depending on programme requirements, testing may cover:
- conducted emissions
- radiated emissions
- conducted susceptibility
- radiated susceptibility
- electrical transients
- power interfaces
- cabling and communication lines
- electromagnetic fields.
As in the Defence and Aerospace sectors, the test setup must be sized according to the frequencies, levels, coupling methods and performance actually required by the programme.
From unit qualification to whole-satellite compatibility
A unit that meets its individual requirements does not automatically guarantee that the complete satellite will be electromagnetically compatible.
Integrating many units can reveal phenomena that were not necessarily visible during individual tests:
- cable-to-cable coupling
- disturbances via power supplies
- common-mode currents
- radiation from digital equipment
- interactions between converters and sensitive equipment
- antenna-to-antenna coupling
- harmonics
- intermodulation products
- spurious emissions in sensitive bands.
System-level EMC therefore consists in ensuring that the various units can operate simultaneously in their operational configurations.
Integration tests must then be designed around the satellite's actual architecture and operating modes that are representative of the mission.
From extremely weak signals to high RF power
Space has one notable feature: extremely different power levels can coexist within the same system.
A telecommunications satellite may, for example, combine high-power RF transmitters with receive chains designed to detect extremely weak signals.
This difference in level calls for particularly rigorous control of:
- spurious emissions
- harmonics
- intermodulation products
- noise
- RF leakage
- coupling between chains
- isolation between transmit and receive.
A disturbance that seems negligible compared with a transmitter's power can become significant once it falls within the band of a highly sensitive receiver.
This issue is the natural link between EMC and RF/microwave engineering.
RF payload and telecommunications
For telecommunications satellites, the payload may include several RF and microwave chains handling the reception, processing, filtering, amplification and retransmission of signals.
Characterising these chains may require measurements covering, in particular:
- RF power
- frequencies
- spectrum
- gain
- insertion loss
- matching
- isolation
- harmonics
- spurious emissions
- intermodulation.
Depending on the application, these measurements may extend to microwave and millimetre-wave frequencies.
The quality of the measurement chain itself becomes decisive when trying to characterise very low spurious levels.
PIM: when a passive component generates new frequencies
PIM (Passive Intermodulation) is a particularly important phenomenon in high-power RF systems, and notably in certain telecommunications payloads.
The principle can be explained simply.
Imagine two RF carriers at frequencies f1 and f2 passing simultaneously through a passive component.
In a perfectly linear system, this component transmits both signals without creating any new frequencies.
In reality, however, a very slight non-linearity may exist at a connector, a metal contact, a cable, a filter, a mechanical assembly or an interface between materials.
This non-linearity can then mix the signals and generate new frequencies: intermodulation products.
Third-order products include, in particular:
2f1 − f2
2f2 − f1
The problem arises when one of these spurious products falls within a sensitive receive band.
The phenomenon can be summarised as follows:
Two high-power RF carriers → slight non-linearity in a passive element → creation of an intermodulation product → spurious signal in a receive band → possible degradation of receiver performance.
Why can PIM become critical in space?
The difficulty stems from the considerable gap between the levels involved.
The RF carriers passing through the chain may be at high power, while the PIM product being sought may be extremely weak.
Yet a satellite receiver is designed precisely to receive very low-level signals.
An intermodulation product that is very weak compared with the transmit carriers can therefore become a problem if it lies within a band used by a sensitive receiver.
This is why PIM is a particularly important issue when a system combines:
high transmit power + multiple carriers + sensitive receivers + dense RF integration.
Where does PIM come from?
PIM may be promoted in particular by:
- imperfect electrical contacts
- connectors or assemblies with poor contact quality
- interfaces between different materials
- surface finishes
- oxidation or contamination
- certain metal junctions
- mechanical or tightening defects
- more generally, any unintentional non-linearity in the RF path or its environment.
Controlling PIM is therefore not solely a matter of electronic design. It also depends on the connectors, mechanics, materials, assembly and build quality of the RF system.
Measuring PIM: a particularly demanding measurement chain
Example: architecture of a high-power PIM test bench:
Take the case of an RF or microwave unit intended for a satellite payload and required to operate simultaneously with two high-power carriers.
To characterise its PIM level, the bench may include two RF generation paths, each associated with an RF or microwave power amplifier. The two amplified carriers are then combined and injected into the equipment under test.
The architecture can be represented simply:
Generator f1 → power amplifier ┐
├→ combining / filtering → EUT → filtering → low-level reception
Generator f2 → power amplifier ┘
The amplifiers make it possible to reproduce the power levels actually encountered by the unit. But they also introduce a difficulty: the bench must guarantee that the intermodulation products measured genuinely come from the EUT and not from the amplifiers or other elements in the chain.
The harmonics and intermodulation products generated by the sources and amplifiers must therefore be very carefully controlled, with sufficient filtering and isolation between the different paths.
After the EUT, a selective receive chain is used to search for the PIM product at the expected frequency, for example for a third-order product:
fPIM = 2f1 − f2 or fPIM = 2f2 − f1
The challenge is then to detect an extremely weak spurious signal in the presence of much more powerful carriers. The dynamic range of the measurement system, filtering and isolation therefore become decisive.
The bench itself must have very low PIM
The amplifiers are only part of the problem. The bench's combiners, filters, couplers, cables, connectors, adapters, loads and mechanical interfaces can themselves contribute to the measured PIM level.
Before characterising the EUT, the residual PIM floor of the test bench itself must therefore be known and controlled.
The challenge could be summarised as follows:
Generate two high-power carriers → combine them without creating significant spurious signals → stimulate the EUT → reject the carriers → measure an extremely weak PIM product.
This is precisely what turns a PIM measurement into an RF/microwave integration project, rather than a simple measurement made with a spectrum analyser.
A typical application of the HEMERA RF multi-brand approach
Building such a bench may require combining very different technologies: RF/microwave generators, power amplifiers, very high-rejection filters, combiners, couplers, low-PIM components, analysers, power sensors and control software.
The choice of amplifiers depends in particular on the frequency band, the power required, linearity and the spectral performance sought. Passive components, for their part, must be rated for the applied power while contributing as little as possible to the bench's residual PIM.
PIM measurement poses a fundamental difficulty: the bench must generate high-power carriers while being able to detect extremely weak spurious products.
The measurement bench must therefore not generate more PIM itself than the equipment being characterised.
A measurement architecture may include, in particular:
carrier generation → amplification → combining and filtering → equipment under test → separation/filtering → reception and measurement of the PIM product.
The bench's cables, connectors, adapters, loads, filters, couplers and other components must offer performance suited to this type of measurement.
The result therefore depends on the performance of the whole chain, not just on the analyser used at the end of it.
This issue illustrates particularly well the value of an integrator's approach: PIM measurement must be treated as a complete RF system.
Harmonics, intermodulation and spurious emissions
PIM is only one of the issues that can affect the RF performance of a payload.
Characterisation may also cover harmonics, active intermodulation products, spurious emissions, noise and other unwanted signals.
The aim is in particular to verify that a transmit chain does not generate energy likely to degrade another satellite function.
This analysis requires thinking simultaneously in terms of:
- frequency
- power
- measurement dynamic range
- bandwidth
- filtering
- isolation
- linearity
- noise.
This is where EMC, RF and microwave expertise complement one another.
Controlling and monitoring the system during testing
As with Defence and Aerospace applications, exposing a unit to a disturbance or performing an RF measurement is not always enough.
The functional behaviour of the EUT must also be verified during the test.
Depending on the complexity of the equipment, it may be necessary to:
- control different operating modes
- drive the interfaces
- monitor power supplies
- monitor communications
- check functional parameters
- log events
- detect anomalies
- synchronise functional data with EMC or RF measurements.
For complex systems, automation makes it possible to coordinate instruments, test sequences, data acquisition and EUT monitoring, improving the repeatability and traceability of tests.
From test setup to system validation
In space, the requirement therefore goes well beyond choosing a generator, an amplifier or an analyser.
Designing the test setup begins with an analysis of:
- programme requirements
- the qualification level considered
- the frequencies to be covered
- the power and levels to be measured
- the required dynamic range
- the EUT interfaces
- the operating modes to be reproduced
- the target RF performance
- monitoring and automation constraints.
Depending on the application, HEMERA RF can integrate RF and microwave generators, amplifiers, antennas, EMI receivers, analysers, network analysers, power meters, probes, couplers, injection devices, shielded or anechoic chambers, PIM measurement chains and control software.
The aim is to build a consistent architecture from signal generation through to the acquisition and processing of results.
The HEMERA RF approach to space projects
HEMERA RF acts as general contractor and multi-brand integrator for the design and delivery of EMC, RF and microwave test facilities.
This approach is particularly well suited to the space sector, where a single installation may require technologies from highly specialised manufacturers.
HEMERA RF can be involved from the technical qualification of the requirement and analysis of the target performance through to sizing, technology sourcing, equipment supply, hardware and software integration, automation, commissioning and metrology follow-up.
Its independence from any single manufacturer means it can seek the most relevant solution for each function: generation, amplification, low-level measurement, spectrum analysis, antennas, microwave components, PIM, shielding, automation or EUT monitoring.
This ability to combine several technologies is particularly important when high RF power, very low measurement levels and wide frequency coverage have to be reconciled.
Expertise from subassembly to space system validation
HEMERA RF draws on its experience of EMC, RF and microwave environments, with coverage from DC up to 110 GHz, to address the challenges encountered in space applications.
This expertise covers the EMC qualification of an electronic unit as well as the characterisation of an RF chain, subsystem integration issues and the electromagnetic interactions encountered at the level of a platform and its payload.
For telecommunications applications, this approach extends to high power, low receive levels, spurious emissions, harmonics and passive intermodulation (PIM).
By combining technical qualification, sourcing from specialised manufacturers, multi-brand integration, automation and metrology, HEMERA RF supports space industry players in delivering high-performance, scalable test facilities tailored to the specific requirements of each programme.
Frequently asked questions
Frequently asked questions
Space
Which EMC standards apply to aerospace and defence?
In aerospace and defence, the standards include:
• RTCA DO-160 for airborne equipment
• its European counterpart, EUROCAE ED-14
• various MIL-STD standards for military applications
• specific requirements for individual programmes and platforms
The exact requirements must be identified before sizing the test setup.
What is an indirect lightning test?
It reproduces:
• transient voltages
• transient currents
• the disturbances that may be induced in wiring and electronic equipment during a lightning event
It concerns induced electrical and electromagnetic effects, not the physical impact of a direct lightning strike on the structure.
What is the difference between the direct and indirect effects of lightning?
• Direct effects: the physical consequences of the lightning current on the structure.
• Indirect effects: transient voltages and currents induced in wiring, interfaces and electrical or electronic equipment.
Which standards govern indirect lightning testing in aerospace?
They include:
• RTCA DO-160 Section 22
• EUROCAE ED-14 Section 22
• other standards or specifications depending on the programme concerned
What is Section 22 of RTCA DO-160 / EUROCAE ED-14?
It covers in particular:
• the susceptibility of equipment to lightning-induced transients
• the applicable waveforms
• test levels
• injection methods
• the corresponding qualification categories
What is the difference between pin injection and cable bundle tests?
Pin injection:
• direct injection of the transient
• applied to pins or interfaces
Cable bundle:
• disturbance applied to the harness
• reproduces coupling onto the installation’s cables
The generators and injection devices may therefore differ.
Which waveforms are used for indirect lightning testing?
The standard specifies different waveforms depending on:
• the coupling mechanism
• the method
• the qualification category
• the test level
• the interface concerned
You therefore need to identify the waveforms to be covered before choosing the generator.
What equipment is needed for testing to RTCA DO-160 / EUROCAE ED-14 Section 22?
Depending on the method:
• transient generators
• injection networks
• transformers or couplers
• calibration fixtures
• current probes
• voltage probes
• acquisition instrumentation
• suitable accessories and loads
How are test levels and waveforms chosen under RTCA DO-160 / EUROCAE ED-14 Section 22?
They depend in particular on:
• the qualification category
• the equipment
• its installation
• the interfaces
• programme requirements
The choice should therefore not be dictated solely by the capabilities of the available generator.
How can the injected current or voltage be measured and monitored during the test?
The measurement chain may include:
• current probe
• voltage probe
• suitable attenuation
• appropriate cabling
• oscilloscope or high-speed acquisition system
The bandwidth and dynamic range of the whole chain must be checked to ensure the measured transient is reproduced accurately.
How do you size a lightning test bench for aerospace equipment?
You need to determine:
• the standard
• the category
• the waveforms
• the levels
• pin injection / cable bundle methods
• harness characteristics
• the equipment to be tested
• measurement and calibration needs
What are the CS114, CS115 and CS116 tests?
These methods correspond to different types of conducted susceptibility in the military domain.
They differ in particular in:
• the type of signal
• the frequency range
• the coupling mode
• the levels
• the equipment required