A design method for asymmetric coupled line impedance transformer with high transforming ratio

This paper presents a design method for asymmetric coupled line impedance transformers. The initial geometric value determined by this method is very closely to the optimal value. Based on the extraction algorithm of per unit length resistance, inductance, conductance, and capacitance of transmission lines, characteristic parameters of the four-port asymmetric coupled line circuit are re-derived and calculated. Image impedances are adopted for the ideal matching design of two-port devices. An asymmetric coupled line impedance transformer with a high transforming ratio of 100 (50 Ω to 0.5 Ω) is designed, fabricated, and measured. The excellent agreement between simulation and measurement results proves the effectiveness of the proposed accurate design method and unique superiorities of asymmetric coupled lines with better initial values.