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 (
$Q_{\mathrm {u}}$
) 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
$Q_{\mathrm {u}}$
, 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.