Tunable VHF Miniaturized Helical Filters

Abstract

In this paper, a miniaturization technique and a tuning concept that enable the realization of highly miniaturized and frequency reconfigurable helical filters are reported for the first time. The proposed filter design is based on tunable helical resonators with an internal volume of only 8.6 cm and variable capacitive loading. A second-order bandpass filter was built and measured as a proof-of-concept demonstrator. The helical filter is manufactured with a CNC process and tuning is achieved through piezoelectrically actuated tuners, which are bonded over the helix apex. A measured center frequency tuning between 257-365 MHz was realized with an insertion loss between 0.3-3.2 dB including connector losses. The measured filter bandwidth varied between 6%-7.7%. Tunable resonators were also manufactured so as to extract the unloaded quality factor. It was measured between 392-639 for a center frequency tuning of 2.5:1 (156.5-395 MHz).

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

“…Various tuning mechanism have been explored to date for 3-D bandpass filters (BPFs). These include p-i-n diodes, RF switches, varactors, stepper motors and RF microelectromechanical systems (MEMS) [3]- [8]. While diodes and switches enable discrete tuning, varactors result in high passband insertion loss (IL) for frequencies >∼0.5 GHz [5].…”

Helical resonator filters with improved multipactor performance exploiting rigorous modelling and the large gap approach

“…This corresponds to an improvement of ∼27 dB in terms of power handling with regard to the classical helical filter [1]. However, this dielectric-filled solution leads to increased complexity in manufacturing (and therefore development time and cost) as well as mass budget, in particular when compared with more advanced solutions for helical filters proposed in [6,7].…”

3-D printed filter based on helical resonators with variable width

“…Helical resonator filters have widespread applications in communication systems operating in the VHF and UHF ranges [1]- [2]. Helical resonators are superior to resonators based on lumped elements, in terms of offering a higher unloaded quality factor (in the range of 500 to 2000) [3]. In contrast to conventional coaxial resonators, helical resonators have advantages of smaller size and volume, at the expense of degrading quality factor.…”