3D-Printing and High-Precision Milling of W-Band Filter Components with Admittance Inverter Sequences

This work presents the design of an additively manufactured W-band bandpass filter and a subtractively manufactured W-band diplexer in order to demonstrate the use of admittance inverter sequences for the ease of manufacture at millimetre-wave frequencies. Contrary to typical impedance inverters (E-plane and H-plane irises), the use of admittance inverters (E-plane and H-plane stubs) allow for larger dimensions to be specified and ultimately do not impede the general waveguide path. The proposed bandpass filter is designed with all E-plane stubs, while the diplexer is designed with one branch utilizing both E-plane and H-plane stubs as an arbitrary sequence, and the second branch utilizing all H-plane irises. The additively manufactured bandpass filter is fabricated using the most elementary level stereolithography (SLA) based methods, demonstrating that a hobbyist-type SLA printer and metallization method can procure exceptional results for millimeter-wave filter designs. The subtractively manufactured diplexer is fabricated using high-precision computer numerical control (CNC) milling in order to highlight the use of arbitrary inverter sequences in a more complex and robust design profile, while the dispersive transmission zeros that are caused by over-moding of the inverter stubs is utilized to demonstrate unique isolation characteristics in the upper W-band region. The design concepts, fabrication profiles, simulations and measurements which are presented in this work highlight a viable option for overcoming miniaturized dimensions in millimetre and sub-millimetre-wave applications.