High linearity RF filter tunes over 3.4 to 11.1GHz

“What’s special about YIG is that it propagates a magnetic spin wave,” said research engineer Troy Olsson.

The team is researching filters for 6G communication in ‘frequency range 3’ – FR3, 7 to 24GHz. “At these higher frequencies, you may not always have a dedicated block of spectrum just for commercial use,” said Olsson, who is proposing tuneable filters as an alternative to switching across a bank of fixed filters.

Architecturally the device is a magneto-static wave filter, formed as a cavity micromachined from thin-film YIG, grown on a gadolinium gallium garnet substrate. Injection and output transducers are aluminium.

This occupies 200 x 70µm and is controlled by an in-plane magnetic bias perpendicular to magnetostatic wave propagation along the length of the YIG.

Tuning is achieved by altering the magnetic field, which comes from a combination of fixed NdFeB magnets, and AlNiCo magnets whose remnance, which is non-volatile, is adjusted using current pulses through coils wrapped around them.

In this way, power is only needed to vary tuning and not to hold a particular tuning.

The whole proof-of-concept including magnets occupies less than 2cm³. Insertion loss is between 3.2 and 5.1dB, and the out-of-band third order input intercept is >41dBm.

Read about the filter in the Nature Communication paper ‘Frequency tunable magnetostatic wave filters with zero static power magnetic biasing circuitry‘, which is clearly-written and can be read in full without payment.

Photo: Black cubes are the fixed magnets and the long dark grey AlNiCo magnets have red coils around them. Magnetic flux is held within the light grey pole pieces, and the filter sits in the central gap.