Tiny YIG Filter Revolutionizes 6G Technology

Wireless communications are on the brink of a significant transformation, thanks to a groundbreaking new filter developed by researchers at the University of Pennsylvania. "I hope it will enable the next generation of wireless communications," says Troy Olsson, Associate Professor in Electrical and Systems Engineering (ESE) at Penn Engineering and the senior author of a new paper in Nature Communications that describes the filter.

The electromagnetic spectrum is a precious resource with only a tiny fraction available for wireless communications. Less than one billionth of one percent of the overall spectrum is suitable for wireless communication. The bands of that fraction of the spectrum are carefully controlled by the Federal Communications Commission (FCC), which recently made available the Frequency Range 3 (FR3) band, including frequencies from about 7 GHz to 24 GHz, for commercial use.

To date, wireless communications have mostly used lower-frequency bands. Olsson explains, "Right now we work from 600 MHz to 6 GHz. That’s 5G, 4G, 3G." However, covering all frequencies or bands requires large numbers of filters that take up substantial space. For example, the typical smartphone includes upwards of 100 filters to ensure that signals from different bands don’t interfere with one another.

One complication posed by using higher-frequency bands is that many frequencies have already been reserved for satellites. Olsson notes, "Elon Musk’s Starlink works in those bands. The military has already been crowded out of many lower bands." To address this challenge, Olsson’s lab designed an adjustable filter that can selectively filter different frequencies, eliminating the need for separate filters.

What makes the filter adjustable is a unique material called "yttrium iron garnet" (YIG), which changes frequency when exposed to a magnetic field. This allows the filter to achieve continuous frequency tuning across an extremely broad frequency band. The new filter can be tuned to any frequency between 3.4 GHz and 11.1 GHz, covering much of the new territory opened up in the FR3 band by the FCC.