Monolithic Multiband Coaxial Resonator-Based Bandpass Filter Using Stereolithography Apparatus (SLA) Manufacturing
Kunchen Zhao, Dimitra Psychogiou
Abstract
This article reports on a new class of additive manufacturing (AM) and monolithically integrated multiband coaxial bandpass filters (BPFs). They are based on <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$N$ </tex-math></inline-formula> in-series cascaded multiresonant sections that each of them consists of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$K$ </tex-math></inline-formula> resonators and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$K - 1$ </tex-math></inline-formula> admittance inverters. In this manner, a transfer function containing <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$K N$ </tex-math></inline-formula> th-order passbands in between <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$K - 1$ </tex-math></inline-formula> 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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$S$ </tex-math></inline-formula> - and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$C$ </tex-math></inline-formula> -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 ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q_{\mathrm{ eff}}$ </tex-math></inline-formula> ) 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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q_{\mathrm{ eff}}$ </tex-math></inline-formula> 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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q_{\mathrm{ eff}}$ </tex-math></inline-formula> above 1100, successfully validating the proposed monolithic multiband coaxial BPF concept.