Continuously Tunable 3-D Printed Helical Resonators and Bandpass Filters Using Actuated Liquid Metals

Altynbek Dyussembayev,Dimitra Psychogiou

doi:10.1109/lmwc.2022.3152014

Abstract

This letter reports on a new class of agile helical resonators and bandpass filters (BPFs) with continuously-tunable center frequency. RF tuning is achieved by altering the liquid metal (LM) volume within an additively-manufactured plastic tube that has the shape of a helix and forms the inner conductor of the helical resonator. A low-cost and versatile integration scheme using 3-D printing and pneumatically-actuated Galinstan is proposed. For proof-of-concept validation purposes, a helical resonator with center frequency tuning between 1 and 1.5 GHz, and unloaded quality factor between 131 and 145 was manufactured and measured. Two BPF porotypes namely: 1) two-pole BPF with center frequency tuning between 1.16 and 1.49 GHz and insertion loss (IL) < 2 dB and 2) three-pole BPF with center frequency tuning between 1.18 and 1.49 GHz, and IL < 2.1 dB, were manufactured and tested at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$L$ </tex-math></inline-formula> -band.

Highlights

F REQUENCY-AGILE RF filters are important counterparts of almost every emerging wireless communication, radar and instrumentation system
Various tuning mechanism have been explored to date for 3-D bandpass filters (BPFs)
It exhibits center frequency tuning between 1.16 and 1.49 GHz and insertion loss (IL) < 2 dB that corresponds to an effective quality factor (Qeff ) of 135–155

Summary

INTRODUCTION

F REQUENCY-AGILE RF filters are important counterparts of almost every emerging wireless communication, radar and instrumentation system. While diodes and switches enable discrete tuning, varactors result in high passband insertion loss (IL) for frequencies >∼0.5 GHz [5] Mechanical tuning schemes such as those using MEMS [5], or stepper motors [4] are slow (e.g., 100–1000 s of μs) and RF MEMS suffer from long-term reliability issues. There exist only two tunable helical BPF topologies using piezoelectric actuators and varactors They have been implemented for low frequencies (up to 320 MHz in [7] and 365 MHz in [8]) due the manufacturing complexity of the helix, the difficulty to realize small capacitive gaps (∼2–10 μm in [8]) and the high varactor loss [7].

TUNABLE LM-BASED RESONATOR CONCEPT

LM-TUNABLE BPFS

Findings

CONCLUSION