A novel T-type dual-band impedance transformer for frequency-relevant complex impedance load

A novel three-section transmission line based T-type dual-band impedance transformer (DBIT) with its closed-form design equations is proposed in this paper. The proposed impedance transformer could transform two different complex impedances to a resistive load at two arbitrary real frequencies. A section transmission line is employed to transform the two different complex impedances to the same complex impedance at the two frequencies first. Another section transmission line is utilized to transform the resistive load terminal to an intermediate complex impedance at the two frequencies, which real parts is equal to the real parts of the first section transmission line. The third section opened or shorted transmission line stub is bestowed to cancel the sum susceptance of the first and second transmission line. The proposed method is especially appropriate when the two designated frequencies are far away from each other.