Inline Quasi-Elliptic Bandpass Filter Based on Metal 3-D Printing Technology

• Published in: IEEE transactions on microwave theory and techniques Vol. 70; no. 4; pp. 2156 - 2164
• Main Authors: Rao, Jiayu, Nai, Kenneth, Marques-Hueso, Jose, Vaitukaitis, Povilas, Hong, Jiasheng
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.04.2022; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: 3-D printers; Band-pass filters; Bandpass filters; Bandpass filters (BPFs); Complexity theory; Controllability; Couplings; Electric filters; Filtering theory; inline structure; Magnetic resonance; metal 3-D printing; Metals; mixed coupling; Printing; Prototypes; Resonators; Three dimensional printing; transmission zeros (TZs); Waveguides
• ISSN: 0018-9480; 1557-9670
• DOI: 10.1109/TMTT.2022.3144275

This article presents a novel waveguide loaded air slots' resonator (WLASR) comprised of a surrounding metal box and inserted metal disk with etched air slots. The proposed WLASR exhibits a comparable unloaded quality factor (<inline-formula> <tex-math notation="LaTeX">Q_{\mathrm {u}} </tex-math></inline-formula>) to the coaxial resonator and allows controlling the electric and magnetic couplings separately. These attractive characteristics were first deployed to design a four-pole inline electrical-magnetic mixed-coupling bandpass filter centered at 2.82 GHz with a fractional bandwidth of 6.73% and two controllable transmission zeros (TZs) located at 2.65 and 2.98 GHz, respectively. Direct metal 3-D printing technology was utilized to manufacture the prototype. The measured results were auspicious for the first demonstrated 3-D printed prototype. Hence, two six-pole filters with multiple TZs, more compact sizes, higher <inline-formula> <tex-math notation="LaTeX">Q_{\mathrm {u}} </tex-math></inline-formula>, and improved shape were designed. For experimental validation, one of them was printed with only two pieces. The measured results agreed well with the simulated ones.