High-Q ceramic filters help overcome GNSS jamming

High-Q ceramic bandpass filters present a technical opportunity to build jamming-resistant GNSS receivers for mission-critical applications, according to a blog by Knowles Precision Devices.

Bandpass filters play a critical role in mitigating GNSS jamming by isolating legitimate satellite signals from interference. These filters are designed to allow frequencies within the GNSS operational bands (GPS L1/L2, Galileo E1/E5) while attenuating out-of-band noise and intentional jamming signals.

With their low cost and compact form factor, surface acoustic wave (SAW) filters are a natural fit for GNSS receivers, but they struggle in high-interference conditions due to limited out-of-band rejection and broader skirts, Knowles’ Peter Matthews explains. While SAW filters continue to meet performance requirements for consumer devices and systems, high-Q ceramic filters offer a robust upgrade for mission-critical applications needing mechanical and thermal stability, predictable tuning characteristics, and long-term reliability. 

Q factor is used as shorthand figure of merit (FOM) for RF filters. In short, Q factor is expressed as the ratio of stored versus lost energy per oscillation cycle. It describes specifications like the steepness of skirts (that is, the selectivity) and insertion loss. Overall, losses through a resonator increase as Q factor decrease and will increase more rapidly with frequency for lower values of resonator Q. 

Knowles’ high-Q ceramic filters offer: 

• Sharp Skirts: Enable precise filtering near the band edges.
• High Rejection: Attenuates out-of-band signals and jammers.
• Low Insertion Loss: Preserves the integrity of weak GNSS signals. 

These attributes are especially important in military and aerospace platforms where GNSS must function reliably in the face of hostile electronic countermeasures. High-Q ceramic filters enable precise frequency discrimination, ensuring that only legitimate GNSS signals reach the receiver.

“Consider a drone conducting reconnaissance in a contested area or an autonomous harvester navigating with sub-inch precision on a farm,” Matthews explained. “Both scenarios require high signal clarity. Knowles’ high-Q ceramic filters, like the GPS L1, are engineered for use in L-band GNSS applications. These filters demonstrate low passband insertion loss (<2.0 dB), high out-of-band rejection (up to 40 dB), and compact dimensions, making them ideal for both portable and embedded systems.

Knowles offers a range of high-Q ceramic filters. See the GPS L1 filter datasheet for detailed specifications.