Ultra-Wideband Asymmetric Impedance Transformer Design for High-Power Amplifier MMICs

In this study, an asymmetric impedance transformer is proposed for broadband high-power amplifier (HPA) monolithic microwaveintegrated circuits (MMICs). The design adopts an asymmetrical coupled line structure as the bias circuit to supply the large drain current required by the HPA. The formula for the asymmetric Ruthroff impedance transformer is derived to optimize the bandwidth, which is then analyzed as a function of the key design parameters. The transformer is designed using a commercial 0.25 μm gallium nitride highelectron- mobility transistor MMIC and fabricated in a meander structure to reduce size. The fabricated circuit exhibits an insertion loss of approximately 0.3–1.8 dB from 6 to 18 GHz. The proposed impedance transformer is also applied to the output matching circuit of a non-uniform distributed power amplifier, and the fabricated power amplifier demonstrates a high output power of up to 30 W from 6 to 18 GHz.