Monolithically-Integrated Bandpass Filters Using Capacitively-Loaded Intertwined Helical Resonators

This paper presents a novel compact 3D bandpass filter (BPF) concept based on new classes of intertwined helical resonators. The concept is demonstrated by three unique RF filter architectures: a second-order single-band BPF, a second-order dual-band BPF, and a differential single-band BPF. The filter designs are based on coupled-resonator theory, and their implementation is performed using stereolithography apparatus (SLA) 3D printing to create monolithic, screwless structures with ultra-low weight (20-65 gr) and minimal loss. The proposed intertwined helical resonator-based BPF concept, which enables designs with compact size and large fractional bandwidth (FBW) with transmission zeroes (TZ), has been experimentally validated. Manufactured prototypes have demonstrated the following RF performance: single-band BPF: center frequency of 1.08 GHz, 3 dB FBW of 15.5%, and insertion loss (IL) of 0.08 dB; dual-band BPF: passbands centered at 0.84 GHz and 1.53 GHz, with a 3 dB FBW of 19% and 6.5% and IL of 0.2 dB and 0.55 dB, respectively; differential single-band BPF: center frequency of 0.78 GHz, 3 dB FBW of 4%, and IL of 0.87 dB. To the best of the author's knowledge, this work is the first approach to 3D-printed differential BPFs.