A 3-D-Printing-Compatible 90°-Bending and Polarization-Rotated Waveguide Filter Based on Capsule-Shape Resonators and Spherical Joints

This paper presents a new class of bending and polarization-rotated waveguide filter with enhanced design flexibility and structural compatibility with additive manufacturing technology. The filter is based on capsule-shape cavity resonators that are coupled with spherical cavity joints. The resonators and coupling cavities are blessed with high rotational symmetry, allowing for flexible design of arbitrary bending and polarization rotation angles between $0^{\circ}-90^{\circ}$ without introducing any distortion of the filter geometry. A $K a$-band fourth-order waveguide filter prototype with bending and polarization rotation angles of 90° and a Cheby-shev bandpass transfer function is designed and implemented. The filter is manufactured monolithically by incorporating high-precision Polyjet 3-D printing and electroless copper plating processes. The RF-measured result of the 3-D printed filter shows a return loss of over $16 \mathrm{~dB}$, an average insertion loss of $1.8 \mathrm{~dB}$, and a small frequency shift of $0.12 \%$ in the passband.