A micromachined spin-wave filter shows how future radios could tune across the 6G spectrum using a single magnetic bias.
Study: Spin-wave band-pass filters for 6G communication. Image Credit: matakeris.creative/Shutterstock.com
The new study in Nature reports a spin-wave (SW) ladder band-pass filter that addresses several challenges in high-frequency radio filtering for emerging 6G systems.
Using a single external magnetic bias, the device demonstrates low insertion loss, wide bandwidth, and multi-octave frequency tunability, all performance metrics that have been difficult to achieve simultaneously in compact, manufacturable platforms.
The work shows how advances in micromachining and magnetic device design could support more flexible radio-frequency (RF) front ends as wireless systems move into the 7-24 GHz FR3 spectrum.
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Future 5G FR3 and 6G networks are expected to operate at higher carrier frequencies while supporting channel bandwidths of hundreds of megahertz or more. That combination places increasing demands on RF band-pass filters, which must offer low loss, strong rejection of nearby interference, high linearity, and compact size.
Below 6 GHz, surface- and bulk-acoustic-wave filters dominate commercial RF systems. At higher frequencies, though, their electromechanical coupling and quality factors degrade.
Spin waves in yttrium iron garnet (YIG), however, naturally support frequency tunability, and their performance improves rather than degrades at higher operating frequencies. Most spin-wave filters still suffer from narrow bandwidths, spurious passbands, or impractically large form factors.
Single-Bias Spin-Wave Ladder Filter
This work set out to address these limitations by integrating an adapted ladder-filter architecture – often used in acoustic filters – into spin-wave devices.
Traditional ladder filters require two resonators with significantly different resonance frequencies, which in magnetic systems typically demands two separate uniform bias fields. That requirement increases system size and complexity.
In this work, the frequency separation is achieved instead through geometry-dependent demagnetization contrasts between series and shunt resonators. As a result, the entire filter operates under a single adjustable magnetic bias field.
The devices were fabricated on YIG films grown on gadolinium gallium garnet (GGG) substrates using a wafer-scale micromachining process. Deep argon ion milling defined the magnetic structures, while electroplated gold formed low-resistance microwave transducers.
A backside anisotropic etch of the GGG left a 10-µm membrane beneath each device, allowing a ground plane to be placed close to the magnetic layer and increasing the effective electromechanical coupling factor to 18 %.
The Ladder Filter's Performance and Trade-Offs
Electrical characterization using small-signal S-parameter measurements yielded minimum insertion losses of 2.54 dB and lithographically defined bandwidths up to 663 MHz.
By sweeping the external magnetic bias from 373.4 to 904.2 mT, the filters were tuned continuously from 7.08 to 21.6 GHz while maintaining near constant absolute bandwidth across much of that range.
As expected for ladder filters, performance depends on filter order. Fifth-order designs achieved stronger out-of-band rejection (up to 24.82 dB), but with higher insertion loss than third-order devices.
The measurements also revealed frequency-dependent limitations: at lower frequencies, weaker resonator coupling led to increased passband ripple, while at higher frequencies, electrically longer transducers reduced rejection as the circuit departed from ideal inductive-divider behavior.
Linearity testing showed in-band third-order intercept points exceeding 11 dBm, with no measurable compression for input powers up to 8 dBm.
Demonstration in a Frequency-Agile Receiver
To evaluate system-level relevance, the team integrated the spin-wave filter into a frequency-agile radio receiver.
A 20 Mbps quadrature amplitude modulation (QAM) signal was successfully transmitted and demodulated while the filter and local oscillator were tuned synchronously using an electromagnet.
In interference tests, the filter rejected a nearby 17.3 GHz interferer while preserving a desired 17 GHz signal, demonstrating strong signal-to-noise-and-interference ratio preservation in a crowded spectral environment.
Spurious responses were strongly suppressed below approximately 18 GHz, consistent with the device design and measurements.
Spin-Wave Ladder Filters May Exceed Requirements
The results demonstrate that spin-wave ladder filters can meet many of the performance requirements for high-frequency RF front ends, while offering intrinsic frequency agility that could reduce the need for large banks of fixed-frequency filters.
The study also highlights remaining challenges, including the trade-off between insertion loss and rejection and the need for compact, tunable magnetic biasing solutions suitable for integrated systems.
While not a finished commercial component, the study provides a technically viable and experimentally validated pathway toward reconfigurable magnetic filters for future wireless platforms.
Further advances in packaging and bias integration will be needed before such devices can be deployed at scale.
Journal Reference
Devitt, C. et al. (2026). Spin-wave band-pass filters for 6G communication. Nature, 1-7. DOI: 10.1038/s41586-025-10057-3
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