A Compact Ka/Q Dual-Band GaAs MMIC Doherty Power Amplifier With Simplified Offset Lines for 5G Applications

In this paper, a Ka/Q dual-band Doherty power amplifier (DPA) with simplified offset lines is implemented in a 0.1- $\mu \text{m}$ gallium arsenide (GaAs) process. It is found that the dual-band transmission lines (TLs) employed in the sub-6-GHz dual-band DPA are not suitable to be used as the offset lines in millimeter-wave (mm-wave) dual-band DPAs due to their large sizes and insert losses. An in-depth analysis reveals that the phase requirement of the offset lines can be relaxed, and the DPA exhibits a reasonable performance in a certain phase-shift range. A novel design method is proposed to realize offset lines using simple TLs, which can satisfy the phase-shift ranges in dual bands by choosing a proper electrical length. To enhance the gain of the DPA, a reversed uneven power splitter is adopted to deliver more power to the main power amplifier (PA). The fabricated DPA achieves an output power of 25.4/25.2 dBm, a peak power-added efficiency (PAE) of 33%/25%, and a 6-dB back-off PAE of 22%/17% at 29/46 GHz, respectively, with a compact size of 2.2 1.4 mm2. Applying a 20-MHZ 64-quadratic-amplitude modulation (QAM) signal with a 7.7-dB peak-to-average power ratio (PAPR), the measured average output power, PAE, and error vector magnitude (EVM) at 29/46 GHz are 18.4/19 dBm, 17%/15%, and 1.5%/1.1% after linearization, respectively. To the best of our knowledge, the proposed DPA is the first demonstration of mm-wave dual-band DPAs that do not require any additional switching or reconfiguration.