Design of mm-Wave Filtering Waveguide Twist With Quasi-Elliptic Response and Spurious Suppression Using 3-D Metal Printing

In this brief, a novel design approach to achieve mm-wave waveguide twists with a quasi-elliptic filtering response is proposed using selective laser melting (SLM) 3-D printing. A 4th-order cross-coupling topology is employed to generate two transmission zeros (TZs) for high selectivity. Unlike typical filtering twists, implemented by smooth or multi-step rotating multi-resonator filters, polarization rotation is realized by simply rotating the input and output ports without twisting the resonators, which reduces the design complexity. In addition to the rotation and filtering functions, three types of defected ground structures (DGSs) are added on the two twist shells to suppress the spurious modes. To verify the concept, two filtering twists with different bandwidths and polarization rotation angles are designed, fabricated, and tested. A good agreement between experimental and simulated results is achieved.