Reconfigurable filter design using liquid metal actuation

Abstract

The emergence of technologies such as 5G, IoT, automotive radar, wireless power transfer, broadband satellite internet, and more has increased the number of devices operating and transmitting in the radio frequency (RF) spectrum. Future systems will need to more efficiently use the spectrum without interference, which requires highly reconfigurable filter designs capable of frequency, bandwidth, and shape control. Research has explored filter tuning mechanisms such as tuning screws, piezoelectric actuators, microelectromechanical systems (MEMS), varactors, and PIN diodes. Liquid metal has been a recent growing area of research because of its potential for higher power, linearity, repeatability, and flexibility. This work presents and validates a novel continuously tunable liquid metal mechanism. A tunable substrate-integrated-waveguide resonator with a 3.8 GHz to 5.9 GHz tuning range is presented. The resonator is then used as the building block for a frequency-tunable second-order filter with measured tuning of 3.4 GHz to 5.7 GHz. This is finally developed into a fully reconfigurable second-order design with wide bandwidth, center frequency, and response shape tuning. It can realize a Butterworth response from 3.8 GHz to 5.6 GHz with either a constant absolute bandwidth from 100 MHz to 200 MHz or a constant fractional bandwidth from 2% to 7% over the entire frequency range. All designs show promising results and demonstrate the capabilities of this liquid metal tuning mechanism for future applications requiring advanced reconfigurability.