Design of a parallel multipath triple-band millimeter-wave filter for 5G/6G communications

Abstract

With the accelerated deployment of 5G-Advanced systems and the exploration of 6G millimeter-wave bands, RF front ends increasingly require compact filters capable of supporting several separated frequency channels while maintaining high selectivity and strong inter-band isolation. This paper aims to address the difficulty of simultaneously realizing triple-band response, compact integration, and out-of-band suppression in millimeter-wave filters. A symmetric parallel multi-path triple-band filter is proposed for the 24, 60, and 95 GHz bands. The design combines three resonant branches, strong coupled-line units, and shunt shorted stubs on an ultra-thin substrate with H = 3 μm and εr = 4.3. The multi-path phase relationship is used to form constructive interference at target passbands and destructive interference at nonresonant frequencies. ADS-based gradient optimization is further employed to tune branch lengths, coupling gaps, and matching-line widths. Simulation results show that the proposed filter achieves return loss exceeding 30 dB in the three passbands and inter-band isolation higher than 40 dB. The results indicate that the proposed topology provides a compact and highly selective filtering solution for multi-standard 5G/6G millimeter-wave front ends.