3D–Printed Tunable Helical Resonators for Miniaturized VHF Filters

In this paper, a 3D-printed miniaturized tunable helical resonator for VHF applications is presented for the first time. The cavity and the helical resonator are 3D-printed while the cavity top cover is a printed circuit board (PCB). The frequency tuning is made possible by using varactor diodes. Direct tapping is used to couple externally into the 3D-printed helical resonator. Coplanar waveguides, realized on the top PCB layer, are utilized to form transitions from the ports to the tap-lines. The proposed 3D-printed helical resonator achieved a measured unloaded quality (Q) factor of 168-239 over a tuned center frequency of 170-240 MHz.