Sourcing EMI/RFI-Shielded Components for Advanced Avionics and Communication Systems

In advanced aircraft systems, mitigating electromagnetic interference (EMI) and radio frequency interference (RFI) is a strict performance requirement. Because avionics and communication systems are expected to operate without error in environments exposed to electromagnetic disturbance from external sources and closely-packed internal subsystems alike, a lack of shielding can result in unwanted noise and signal distortion or completely impair their functionality. In this blog, we will cover some avionics and communication system components that incorporate shielding characteristics, as well as provide some general tips to make sure any parts you choose to source are completely effective in combatting EMI and RFI.

Common EMI/RFI-Shielded Components

Shielded Cables

• Braided shield cables: These braided cables use a woven layer of metal strands to surround the conductors, creating a durable, low-impedance shielding path while providing effective attenuation across lower and mid-frequency ranges.
• Foil-shielded cables: Containing a thin metallic foil that is wrapped around the insulated conductors, foil shields provide nearly complete coverage and strong attenuation at higher frequencies. While less robust than braided shields, foil-shielded cables are effective for applications where high-frequency noise suppression and compact cable diameter are priorities.
• Combination braid-and-foil cables: Integrating both of the previous shielding methods results in broad-spectrum EMI/RFI protection for demanding avionics environments.
• Shielded twisted-pair cables: These cables consist of pairs of insulated conductors that are twisted together to reduce electromagnetic coupling and crosstalk, with an additional overall conductive shield applied around the conductors. 

Shielded Connectors

Connectors are interface points where power, data, and radio-frequency signals transition between wiring and electronic equipment. Because these interfaces are natural discontinuities, they are particularly vulnerable to EMI and RFI if not properly engineered. To combat this, aviation connectors are designed with features like:

• Conductive connector shells: Metallic shells provide a continuous conductive path between the cable shield and the equipment enclosure, helping the connector to contain electromagnetic fields and uphold grounding integrity.
• EMI backshells: Attached to the rear of the connector, backshells provide a controlled method for bonding cable shields directly to the connector shell, boosting their ability to contain EMI/RFI while also aiding with strain relief and environmental protection.
• Filtered connector options: For applications with stringent EMI and RFI limiting requirements, certain connectors integrate capacitive, inductive, or combined filtering elements at individual contacts.
• Threaded, bayonet, or quick-lock coupling mechanisms: These coupling styles facilitate secure mechanical engagement under vibration and shock, conditions which could otherwise knock the connector out of place and negate any shielding additions used.

Enclosures

Ferrite Components and Integrated Filters

• Ferrite beads: These are compact surface-mount or through-hole components that are placed close to noise sources or sensitive inputs on printed circuit boards, where they help suppress high-frequency interference at specific points along a signal path.
• Ferrite cores and chokes: Cores and chokes are larger ferrite structures that encircle one or more conductors within a cable assembly or power line, providing effective common-mode noise suppression at subsystem boundaries and equipment interfaces.

Best Practices for Sourcing EMI/RFI-Shielded Components

• Verify compliance with applicable standards like RTCA/DO-160 for commercial airborne equipment and MIL-STD-461 for military systems, which establish defined limits for electromagnetic emissions and susceptibility.
• Evaluate expected interference sources and frequency ranges, including emissions from onboard electronics and exposure to external transmitters. Use this information to select components with documented shielding effectiveness or attenuation performance, often specified in decibels over applicable frequency bands.
• Select materials and surface treatments that provide an effective balance of electrical conductivity, corrosion resistance, mechanical durability, and weight in alignment with an aircraft’s operating environment and regulatory constraints.
• Even with the best component choices made, shielding effectiveness ultimately depends heavily on correct installation. Cable shields, connector shells, and enclosures must be properly terminated and bonded to conductive structures in order to maintain electrical continuity and prevent unintended impedance.

Turn to ASAP Aerospace for Shielded Avionics and Communication System Components