A 0.22–26.5-GHz Ultra-Wideband Directional Coupler Based on Copper Additive Manufacturing

Abstract

This brief presents a compact (5mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times 56$ </tex-math></inline-formula> mm) and ultra-wideband directional coupler fabricated by copper additive manufacturing. The coupler is directly synthesized through the even/odd mode extraction algorithm and realized from a pair of coupled air-filled rectangular coaxial lines with working frequency of 0.22-26.5GHz (usable to 10MHz). Periodically loaded polymer strips are embedded with the air-filled coaxial lines to support the inner conductor but this strips also deteriorate the directivity of the coupler. To alleviate this, a special arrangement of the polymer strips is proposed to decrease the unwanted coupling through the strips. As an example, a 27 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\mathrm{ th}}$ </tex-math></inline-formula> -order coupler is designed and fabricated, the simulated and measured results have good agreement, showing 20dB of return loss (RL) at all ports, 17dB of coupling, <1.33dB insertion loss (IL), >120 times of frequency ratio and 10-20dB of directivity.