Design of a 28-GHz SiGe Doherty Power Amplifier Using Meandered Coupled-Line Couplers

This paper presents a 28-GHz SiGe Doherty power amplifier (PA) that employs transformer-based matching networks and meandered coupled-line couplers to reduce chip area. Quasi-balanced and Doherty operating modes are experimentally evaluated and compared. In Doherty mode, the fabricated PA exhibits a small-signal gain of 30.1 dB. Under large-signal excitation, it achieves a saturated output power of 24.6 dBm with a peak power-added efficiency (PAE) of 31.2%. At 6-dB output back-off, the PAE remains 16.3%. With a 400-MBd 64-QAM signal, the PA delivers an average output power of 14.8 dBm and a PAE of 7.7%, at an EVM level of -25.3 dB.