EMI Filters: The First Line Of Defense In Military/Aerospace Electronics

By Johanson Dielectrics

When failure is not an option, high-reliability EMI filters deliver superior high-frequency EMI suppression for mission-critical applications in aerospace and defense.

When electronic devices receive strong electromagnetic waves, unwanted electric currents can be induced in the circuit, interfering with intended operations. In military and aerospace systems, such failures can compromise mission performance, put multimillion-dollar assets at risk, and even cost human lives.

EMI filters are one of the first lines of defense against these disruptions. EMI filters are passive electronic components designed to suppress high-frequency noise and prevent electromagnetic interference from disrupting sensitive systems.

Unmanned aerial vehicles, advanced radar installations, satellites, and aircraft all rely heavily on high-frequency communications for navigation, real-time situational awareness, target detection and tracking, remote control, and secure coordination.

They also concentrate a significant volume of electronics in close proximity, including high-speed digital circuits, switching power supplies, communication modules, and RF transmitters. Frequently, these operate alongside sensitive GPS receivers, navigation units, and camera or radar payloads.

If strong EMI suppression measures are not in place, the myriad of subsystems may disrupt one another, which can degrade performance or lead to outright failure.

EMI filters, therefore, play a critical role in ensuring high-frequency signals remain clean enough for reliable transmission and reception.

High Reliability EMI Filters

High reliability refers to the design and manufacturing of systems, components, or processes that must operate consistently under mission-critical or extreme conditions, such as extreme heat, vibration, or radiation. These principles apply to satellites, missile guidance systems, and aircraft avionics, where false targets, momentary GPS positioning errors, unstable radar tracking, and corrupted data can compromise mission performance.

When drones malfunction due to interference, for example, there is no option for human intervention. Momentary glitches can trigger a fail-safe mode, force an early return, or cause a crash. For long-range drones operating beyond visual line-of-sight, uninterrupted data flow can be the difference between completing a reconnaissance mission and losing the asset.

 

Military drones also operate in electromagnetic environments that may be intentionally hostile, with adversaries attempting to jam, spoof, or use high-powered radar signals to disrupt operations. By maintaining clean, interference-free power and signal pathways, EMI filters allow drones to perform extended missions with precise navigation, secure communications, and high-fidelity data transmission, even in environments saturated with electromagnetic challenges.

Radar systems face similar challenges. These systems generate and process very weak signals that can be easily corrupted by EMI from external sources such as communication equipment, power electronics, or even other radar systems operating nearby. EMI filters are required to ensure that radar receivers can detect and process genuine signals without distortion or degradation to improve the accuracy of target detection, tracking, and identification. For phased array radars, EMI filters also help preserve the phase and amplitude consistency between hundreds or thousands of T/R modules, ensuring precise beamforming.

EMI Filters

EMI filters normally consist of passive components, such as capacitors and inductors, connected to form circuits designed to shunt unwanted high-frequency energy to ground to suppress high-frequency noise and prevent electromagnetic interference from corrupting sensitive RF, timing, and control circuits.

The inductors allow DC or low-frequency currents to pass through, while blocking the harmful, unwanted high-frequency currents. The capacitors provide a low impedance path to divert the high-frequency noise away from the input of the filter, either back into the power supply or to the ground connection, effectively removing it from the signal or power line.

Unlike commercial applications, high-rel EMI filters must operate flawlessly despite rapid thermal cycling, constant vibration, high humidity, and rapid changes in atmospheric pressure. A failure in the filter, whether from degraded capacitors, saturated inductors, or broken connections, can allow noise to bypass suppression measures.

To maintain performance under these stresses, military and aerospace-grade versions are manufactured with stable dielectric materials that maintain capacitance and balance to minimize parasitics. EMI filters also undergo stricter manufacturing controls, often with 100% visual and electrical inspection and traceability for every material lot.

Components are encapsulated, potted, or housed in metal enclosures to resist mechanical shock and provide effective shielding. Temperature-compensated ferrites, thin film coatings, and ceramic capacitors further improve performance and reliability.

Military-grade electronics are subjected to environmental stress screening and redundancy measures to ensure continued operation even if one conversion stage fails. Components may also be tested to MIL-STD-461 standards for electromagnetic compatibility.

To meet these requirements, components are typically sourced from aerospace or military certified suppliers such as Johanson Technology of Camarillo, Calif. For more than 60 Years, the company has designed and manufactured multi-layer ceramic capacitors, EMI filters, and other critical components for high-reliability applications.

While manufacturing is performed in North America to support scalable production, expedited lead times, and ITAR compliance, all high-reliability testing and design to standards such as MIL-PRF-31033, MIL-STD-202, and MIL-PRF-55681 is conducted in the United States.

To meet the diverse requirements of military and aerospace applications, Johanson Technology offers EMI filters in a variety of configurations and form factors. Depending on the application, filters can employ differential-mode and common-mode elements, transient suppression, and shielding techniques. They may be integrated into power entry modules, cable assemblies, or engineered as custom solutions for compact avionics and mission-critical systems. In many cases, some degree of customization is required.

Monolithic EMI Filter

One example of a unique high-rel configuration unique to Johanson Technology is its monolithic EMI filter, a multilayer ceramic component designed to provide both EMI suppression and power decoupling in a single, compact surface-mount device. The filter features ultra-low parasitic inductance, resulting in a wide filter stop-band.

Unlike standard capacitors with some incidental filtering ability, these EMI filters are engineered for symmetrical, broadband noise suppression across differential and common modes simultaneously, making them exceptionally effective for crowded, noisy environments.

Compared to traditional single capacitors and simple feedthrough filters, monolithic filters offer improved performance in broadband attenuation, lower parasitic inductance, and better high-frequency characteristics. Because of this, they are often chosen for filtering on power/data lines and high-speed signal paths where space efficiency and EMI compliance are critical.

The filter’s innovative electrode architecture allows it to deliver superior performance to conventional multilayer capacitors. Unlike conventional capacitors that use two electrodes, the X2Y structure incorporates a third shield electrode that surrounds the other two.

Because of this balanced structure, the monolithic filter functions as a pair of matched shunt capacitors to ground. The opposing current paths naturally cancel inductance, yielding extremely low equivalent series inductance (ESL). This allows the device to perform broadband EMI filtering, typically effective from around 100 kHz up to well beyond 17 GHz.

The EMI filters are specialized multilayer capacitor arrangements with tightly matched impedance. Therefore, they exhibit very low noise-mode conversion, resulting in a huge improvement in both conducted and radiated emission performance. When compared to typical common-mode chokes, the X2Y EMI filters exhibit 17dB better noise mode conversion. 

By combining differential-mode and common-mode suppression in one element, the EMI filter can often replace several discrete capacitors and inductors that would be required. By some estimates, this can reduce costs by 50% with a corresponding 80% reduction in size.

Filtered Connectors

Planar and discoidal filters incorporate built-in filtering components directly into the connector body to suppress unwanted EMI or radio frequency interference (RFI) as signals or power pass through the connection point. These connectors are commonly used in environments where cables and interconnects function as antennas that can pick up or radiate interference, such as high-speed data lines, control signals, or DC power converters.

Discoidal filters are ring-shaped capacitors frequently installed in EMI filter assemblies to provide feed-through protection against high-frequency interference in radar systems, secure communications, and power units for aircraft and drones.

Johanson Technology’s X7R discoidal filters, for example, feature multilayer ceramic construction and a geometry that enables dramatically lower equivalent series resistance (ESR) and equivalent series inductance (ESL), critical features in high-frequency decoupling and filtering.

Circumferential grounding provides infinite paths to ground, ensuring optimal filtering performance of the filter. The durable substrate construction protects against damage caused by thermal and mechanical stresses.

Often used in sensors and transducers, planar filters employ a flat, layered structure that integrates many filter lines into a single, thin unit, ideal for high-density connectors. They provide superior filtering performance, mechanical strength, and are more compact than discrete solutions such as tubular capacitors.

Size Reduction

All these filters address a key concern for military and aerospace applications: the ability to miniaturize passives allows engineers to meet strict size, weight, and reliability demands while increasing capability and lowering cost.

Miniaturization also improves survivability, since smaller components tolerate vibration and g-forces better than bulky ones, reducing the risk of fatigue failures in high-stress flight conditions. Small, high-quality passives also manage the thermal extremes, radiation, and vacuum of space more reliably when designed with stable materials and geometries.

In military and aerospace applications where failure is not an option, EMI can be a threat to mission success and safety.

As the first line of defense against electromagnetic challenges, high-reliability EMI filters serve as a critical safeguard, preserving the integrity of power and signal pathways against disruptive noise. By ensuring clean, interference-free operation, EMI filters safeguard the precision of military and aerospace systems, protect secure communications, and preserve critical data integrity, even in environments saturated with electromagnetic noise.

For more information, contact Johanson Dielectrics at (805) 389-1166, visit the website: https://www.johansontechnology.com/ppr/military-aerospace/, or e-mail: kvilla@johansontechnology.com. The company is located at 4001 Calle Tecate, Camarillo, CA 93012.