This letter presents a new tuning method for coaxial cavity resonator-based bandpass filters (BPFs). The proposed tuning mechanism lays its foundations on pneumatically-actuated Galinstan that functionalizes the inner conductor of a capacitively-loaded coaxial cavity resonator. By altering the volume of Galinstan (i.e., height of inner conductor), ultrawide (>octave) and low loss RF tuning can be obtained without the need for small capacitive gaps that typically limit the RF performance of coaxial BPFs. To validate the concept, a coaxial cavity resonator with frequency tuning between 2.9 and 9.9 GHz (3.4:1 tuning range), and unloaded quality factor between 120 and 625 was manufactured and measured. Furthermore, the RF performance of a two-pole BPF with: 1) tunable frequency between 3.4 and 7.5 GHz (2.2:1); 2) an intrinsically switched-off state; 3) insertion loss <1 dB; and 4) return loss <10.5 dB was experimentally validated.

中文翻译：

---

使用致动液态金属柱的基于可调谐同轴腔谐振器的滤波器

这封信提出了一种基于同轴腔谐振器的带通滤波器 (BPF) 的新调谐方法。所提出的调谐机制以气动驱动的 Galinstan 为基础，它使电容加载的同轴腔谐振器的内导体功能化。通过改变 Galinstan 的体积（即内导体的高度），可以获得超宽（> 倍频程）和低损耗的 RF 调谐，而无需通常会限制同轴 BPF 的 RF 性能的小电容间隙。为了验证这一概念，我们制造并测量了一个同轴腔谐振器，其频率调谐在 2.9 至 9.9 GHz（3.4:1 调谐范围）之间，空载品质因数在 120 至 625 之间。此外，两极 BPF 的射频性能具有：1) 3.4 和 7.5 GHz (2.2:1) 之间的可调频率；2) 本质上关闭状态；3) 插入损耗<1 dB；4) 回波损耗 <10.5 dB 已通过实验验证。