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

This brief presents a compact (5mm× 56mm) 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 27ᵗʰ-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,120 times of frequency ratio and 10-20dB of directivity.