A novel dual-band 90-degree coupler with harmonic suppression using open-ended stubs and spiral lines

Abstract This paper presents the design and performance evaluation of a small-size dual-band 90° coupler optimized for operation at 2.42 GHz and 4.9 GHz, making it suitable for applications in 5G communication systems. The proposed coupler uniquely integrates open-ended stubs and spiral lines to achieve significant harmonic suppression, effectively eliminating unwanted harmonics up to the 7th order. This makes the design highly efficient for 5G bands, where minimizing interference and maintaining signal integrity are critical. The dual-band capability of the coupler is demonstrated with minimal insertion loss, with S21 ​parameters of 0.3 dB at 2.42 GHz and 0.8 dB at 4.9 GHz, and acceptable coupling S31 ​of 0.12 dB and 1.36 dB, respectively. The design also maintains a compact footprint, occupying an overall area of just 91.2 mm 2 ( <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <m:mrow> <m:mn>0.009</m:mn> <m:mtext> </m:mtext> <m:msubsup> <m:mi>λ</m:mi> <m:mi>g</m:mi> <m:mn>2</m:mn> </m:msubsup> </m:mrow> </m:math> $0.009\hspace{0.17em}{\lambda }_{g}^{2}$ ), making it one of the smallest couplers compared to existing designs. The fractional bandwidths (FBW) achieved are 22.72 % at 2.42 GHz and 12.93 % at 4.9 GHz, indicating robust performance across both frequency bands. The measurement results closely align with the simulated data, confirming the accuracy and effectiveness of the design approach. This work uniquely integrates open-ended stubs and spiral lines, demonstrating a novel dual-band coupler with superior harmonic suppression for 5G.