A broadband and low-loss Ruthroff 4∶9 transmission-line transformer using coupled Microstrip lines

This paper presents a Ruthroff type spiral un-to-un transmission-line transformer (TLT) with impedance transformation ratio of 4:9. Our TLT is fabricated in Microstrip lines technology and covers a chip area of 1.02 mm × 1.12 mm. The simulated minimum insertion loss is 0.19 dB at 5.4 GHz, and the correspondent bandwidth of this TLT is 5.4 GHz (when the insertion loss exceeds 1 dB).