Full-Metal Omnidirectional Filtenna Array Using 3-D Metal Printing Technology

This article proposes a full-metal omnidirectional series-fed filtenna array. The antenna is primarily composed of an outer metal shell, a built-in metal post and three pairs of open-circuit branches. To achieve horizontal omnidirectional radiation, a circular groove is dug on the outer metal shell. Additionally, the built-in metal post is connected to the coaxial feed and shorted at the end with the outer shell. The antenna’s filtering principle can be interpreted as a second-order bandpass filter without any transmission zeros. To enhance out-of-band suppression, three pairs of open stubs have been introduced. And then, three radiation nulls are incorporated to improve frequency selectivity and out-of-band suppression without increasing additional circuit size. Finally, a 3-D-printed series-fed filtenna has been fabricated and measured. The −10-dB
$\lvert S_{11} \rvert $
impedance fractional bandwidth is 3% (ranged from 2.79 to 2.875 GHz), the antenna peak gain is 6.6 dBi, and the three radiation nulls are located at 2.55, 2.69, and 3.09 GHz, respectively. The measured out-of-band suppression is 28 dB.