3-D Printed Dual-Band Filter Based on Spherical Dual-Mode Cavity

A new dual-band bandpass filter (BPF) is designed and fabricated based on a pair of spherical dual-mode resonant cavities using 3-D printing technology. By elaborately introducing three-type metallic posts into each cavity to perturb the degenerated TM101 modes in a reasonable way, a dual-band coupling topology is developed in the design accordingly. Owing to the cross-coupling paths in the designed topology, two transmission zeros (TZs) are successfully introduced between the passbands, bringing out a high band-to-band isolation. Even more, TZs can also be generated by creating additional internal coupling paths to the presented dual-band coupling topology. Besides, the spherical cavity provides a higher quality factor and wider stopband, compared to that of a square or cylindrical cavity. To validate the design concept, a dual-band BPF prototype, operating at 12.0 and 12.5 GHz with respective bandwidths of 120 and 240 MHz, is implemented by 3-D printing process. The measured results exhibit good agreement with the simulated ones, showing more than 20-dB return losses and 20-dB dual-band isolation.