Broadband Planar 5:1 Impedance Transformer

This letter presents a broadband Guanella-type planar impedance transformer that transforms 50 Ω to 10 Ω with a 10 dB bandwidth of 1-14 GHz. The transformer is designed on a flexible 50 μm thick polyimide substrate in microstrip and parallel-plate transmission line topologies, and is inspired by the traditional 4:1 Guanella transformer. Back-to-back transformers were designed and fabricated for ch...