A K/Ka Dual-Band GaN MMIC Doherty Power Amplifier Using Dual Out-of-Phase Current Combining

A novel design approach of a dual-band monolithic microwave integrated circuit (MMIC) Doherty power amplifier (DPA) with an extended back-off range is presented, especially enabled by a dual out-of-phase current combining technique. Benefiting from the proposed strategy, the back-off performance of one DPA is consistent regardless of whether the carrier current phase leads or lags the peaking phase, as long as the absolute phase difference remains constant, thus expanding the design impedance space. In this case, quadruple impedance states demanding necessary matching conditions for dual-band DPA operation at both saturation and back-off across two frequency bands must be addressed. For such a purpose, a composite output network consisting of an impedance transformation line and a dual-band <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pi $</tex-math> </inline-formula>-type network is proposed. By leveraging the intrinsic phase dispersion of the amplifier branches and incorporating a phase compensation network, dual-band and dual out-of-phase current combining is realized. The proposed method is adaptable to any dual-band configuration by appropriately selecting network parameters, thereby enabling flexible back-off enhancement across arbitrary frequency ratios. For demonstration, a K/Ka dual-band MMIC DPA is implemented in a commercial 0.15-<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $</tex-math> </inline-formula>m gallium nitride high-electron-mobility transistor (GaN-HEMT) process. The fabricated DPA shows a saturated output power of 34.9/34.3 dBm, a saturated power-added efficiency (PAE) of 30.8%/22.1% in 18/27.5 GHz, with a compact size of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.6\times 2.3$</tex-math> </inline-formula> mm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>. The PAE at 6-dB power backoff (PBO) is 30.5%/23.4%, and the 9-dB PBO PAE is 24.2%/19.0% in the two operation frequencies.