Abstract: This paper proposed a low-cost wideband 90°balun. The balun circuit consists of a broadband coupled line Wilkinson power divider and wideband 90°phase shifter, which comprises a weakly coupled transmission line cascaded by an open radial stepped impedance resonator. It is implemented by microstrip circuit at the centre frequency of 1. 65 GHz and simulated with the Ansoft High Frequency Simulation Software (HFSS). The balun is fabricated with PCB process and measured by a vector network analyzer. The simulated results and measured results show good agreement. The measured band width is 117. 0% from 0. 65 to 2. 58 GHz for the return loss better than 12. 6 dB, the isolation better than 13. 1 dB, insertion loss lower than 0. 5 dB, and phase deviation less than 90°±7. 6°in the band. Compared with the existing balun structures, the design not only achieves larger bandwidth and single layer circuit layout, but also has the advantages of easy processing and low cost.