Tunable 3D-Printed Coaxial-Cavity Filters with Mixed Electromagnetic Coupling

This paper reports on 3D-printed coaxial-cavity bandpass filters (BPFs) with multiple levels of transfer function tunability. These include: i) center frequency tuning, ii) bandwidth (BW) tuning and iii) intrinsic switching-off. They are based on a new type of mixed electromagnetic coupling that facilitates the realization of a tunable transmission zero (TZ) that is exploited for the tuning of the BPF's BW and its out-of-band isolation. Center frequency adaptivity is obtained by incorporating linear actuators on top of the cavity walls. A proof-of-concept two-pole/one-TZ BPF with tunable frequency between 1.3-2.2 GHz and BW between 59-98 MHz was manufactured and measured.