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

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 (Qᵤ) 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, higherQᵤ, 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.