Single part microwave filters made from selective laser melting

This paper presents waveguide filters manufactured using an innovative manufacturing technique known as Selective Laser Melting (SLM). Two types of narrowband direct coupled cavity filters of fifth degree with a fractional bandwidth of 0.9% have been designed as a first evaluation of this technology for RF application. Both designs have the same frequency response but different internal waveguide geometries. The baseline design consists of rectangular cavity cross sections and rectangular inductive irises. For the second design the new geometry freedom was exploited and cavity and iris shaping techniques have been used to help minimize losses. Altogether, three sets of filters have been fabricated from aluminium alloy and titanium. Q measurement results of the filters made from the raw material, polished and silver plated are presented. It is found that high filter Q efficiency in the order of 70% or more can be achieved if a surface treatment is applied. In addition, the cavity and iris shaping employed, is reported to improve the effective filter resonator Qs over the baseline by at least 15%.