Additive Manufacturing of Interdigital Filters with Arbitrary Line Cross Section

This article investigates the novel use of additive manufacturing (AM) in the production of interdigital cavity filters. It is found that AM enables the production of interdigitated pins of complex cross-sectional geometry, leading to the development of a suitable synthesis method using a commonly available 2-D eigenmode port impedance solver. The method is validated by manufacturing an L-band interdigital filter of 70% fractional bandwidth with triangular bars through selective laser melting, as well as a classical design using rectangular bars. It is found that triangular bars obtain similar coupling to rectangular bars over the average of 35% wider spacing gaps, reducing its sensitivity to manufacturing error. In addition, neither filter requires postproduction tuning, although the bars do warp slightly during printing. These results illustrate the advantages of using AM for the synthesis of wideband interdigital filters.