Reduce Risk and Improve Performance with RFI/Cosite Analysis

Radio frequency interference (RFI) analysis identifies and mitigates unintended electromagnetic energy that can degrade performance, cause failures, or prevent platform compliance. By understanding where interference originates and how it affects sensitive systems, teams can resolve issues early and avoid costly late-stage redesigns.

Electro Magnetic Applications, Inc.  (EMA) has decades of experience in aerospace and defense, consumer electronics, and automotive industries guiding companies through all phases of the design cycle to avoid RFI and ensure success.

EMA can:

• Predict cosite interference on a platform including the affected channels
• Calculate the magnitude of these problems
• Determine mitigation strategies

Understanding RFI and Cosite Interference

RFI occurs when a threat signal causes degradation in a receiver’s performance or prevents the receiver from operating all together. Cosite interference is a subdivision of RFI where the source of interference comes from the platform itself. Multiple radio frequency (RF) systems can operate simultaneously on a platform, but they must be able to co-exist without interference. To ensure systems operate as intended, RFI analysis must be included as part of the design process.  

In-Band vs. Out-of-Band Interference

In-band interference is when transmitter (Tx) signals fall within the receiver’s (Rx) passband. This can introduce harmonics and spurious emissions from the Tx system, intermodulation products generated by multiple Tx’s interacting through nonlinear components, and broadband noise.

Out-of-band interference occurs when Tx signals fall within the receiver’s out-of-band response. These signals can produce unwanted mixer products and spurious responses within the Rx.

When interference exceeds acceptable thresholds, it can desensitize the receiver by reducing its dynamic range, degraded overall system performance, and potentially results in jamming.

Effective RF Cosite Analysis

RF cosite analysis begins by defining the RF architecture. Designers must fully specify each component including specific radios, filters, and diplexers. EMA brings deep expertise in state-of-the-art aerospace system design and extensive experience conducting component trade studies. Figure 1 shows an example of generic RF architecture.

Step two focuses on collecting detailed information for call components. This step is started as early as possible since it relies on coordination with component vendors. Measured data is preferred, but when it is unavailable, EMA can apply assumptions if needed.

Next, EMA builds the initial Ansys EMIT simulation to organize RF system performance data, simulate interference, and mitigate problems. EMIT calculates the electromagnetic interference (EMI) margin in decibels (dB), producing an EMI risk matrix. Model inputs include radio performance parameters, component S-parameters, and manufacturer specification sheet values. Figure 2 shows example EMIT models.

If interference is predicted, engineers evaluate antenna-to-antenna coupling. Antenna models are analyzed in Ansys HFSS to verify radiation patterns and ensure the results are physically realistic. The resulting S-parameter files are then imported back into EMIT for further analysis.

Common mitigation strategies include:

• Repositioning antennas
• Selecting alternative frequency channels
• Adding or refining filters
• Adjusting clock types or operating frequencies
• Modifying materials to reduce coupling

Protect Your Platform

RFI is a serious threat that can be costly if caught late. Using tools such as EMIT and HFSS, EMA delivers accurate risk assessments for each Tx/Rx combination on a given platform.

Gain confidence in your design decisions with RFI analysis from EMA. Our dedicated RF engineers specialize in antenna modeling and installation simulation to maximize accuracy. Click here to get started.