I. Introduction
At present, the 5G system adopts multiple-input multiple-output (MIMO) technology to improve speed, and the system channels are upgraded to 64 or even 128 [1]. As a consequence, the size of a single PA is required to be miniaturized, and PA needs to be integrated into a monolithic microwave integrated circuit (MMIC). Compared with CMOS with low power density and GaN with a high price, GaAs is a compromise choice for MMIC chips for its watt-level output power capability, high efficiency, and affordable price.