A monolithic stereolithography 3-D printed Ka-band spherical resonator bandpass filter

This paper presents a monolithic integration of a Ka-band fourth-order spherical resonator bandpass filter that is fabricated with a ceramic-filled resin using a stereo-lithography-based 3-D printing technique. The filter is designed with a quadruplet coupling topology to improve its out-of-band rejection, and is printed as a single structure instead of multiple parts, without the need of post-fabrication assembly. Surface metallization of the printed resin model is achieved by employing electroless nickel/copper plating. The demonstrated filter prototype exhibits in its passband from 33.9 to 35.7 GHz an insertion loss of 1.7–3.1 dB, a return loss mostly greater than 16 dB, and a center frequency shift of 0.57%.