Compact Quasi-Elliptic Filters With Mushroom-Shaped Resonators Manufactured With 3-D Printer

Additive manufacturing (AM) has proven to be a very interesting technology for a wide range of applications. In this paper, a stereolithography (SLA) 3-D printer has been used for the manufacturing of a new class of filters whose resonators consist of two mushroom-shaped posts transversely placed in a cavity. Each resonator implements a transverse doublet able to produce two poles and two transmission zeros in the upper stopband. The two mushroom stems are connected through a metal wire, whose the position and shape allow the control of the doublet parameters. Higher order filters are obtained by cascading doublet resonators through metal wires in an in-line configuration. This results in filters with nonconventional geometry that can be manufactured thanks to the high flexibility of AM technology. Structures manufactured by SLA are in plastic; thus, a metallization process is required. Here, the filters manufactured have been electroplated with copper. A four-pole filter with four transmission zeros has been designed and manufactured in order to demonstrate the feasibility of the structure proposed.