Monolithic Multiband Coaxial Resonator-Based Bandpass Filter Using Stereolithography Apparatus (SLA) Manufacturing

This article reports on a new class of additive manufacturing (AM) and monolithically integrated multiband coaxial bandpass filters (BPFs). They are based on N in-series cascaded multiresonant sections that each of them consists of K resonators and K - 1 admittance inverters. In this manner, a transfer function containing K N th-order passbands in between K - 1 stopbands can be realized. A monolithic stereolithography apparatus (SLA)-based integration concept is proposed for these BPFs for the first time. For proof-of-concept validation purposes, multiple multiband BPF prototypes at the S - and C -bands were designed, manufactured, and tested. They include: 1) a dual-band second-order BPF with passbands centered at 3.7 and 4.2 GHz, fractional bandwidths (FBWs) of 8.1% and 4.2%, and effective quality factors ( Q-{mathrm{ eff}} ) above 1000 for both of its passbands; 2) a dual-band third-order BPF with passbands centered at 3.7 and 4.0 GHz, FBWs of 4.9% and 3.3%, and Q-{mathrm{ eff}} above 1300; and 3) a triband second-order BPF with passbands centered at 3.5, 3.7, and 4.2 GHz, FBWs of 4.6%, 2.7%, and 5.5%, and Q-{mathrm{ eff}} above 1100, successfully validating the proposed monolithic multiband coaxial BPF concept.