A 26-GHz GaN MMIC Load-Modulated Balanced Amplifier With Miniaturized Dual-Loop Coupler

This article presents the analysis and design of a 26-GHz RF-input load-modulated balanced amplifier (LMBA) using a miniaturized dual-loop (MDL) coupler, implemented in a 0.12- $\mu\text{m}$ gallium nitride (GaN) high-electron-mobility transistors (HEMTs) process. The MDL coupler is proposed to reduce the chip area while ensuring good isolation without compromising the load modulation of the LMBA. The design space of the coupler is expanded by employing dual-loop coupled lines with shunt and coupling capacitors. The miniaturized coupler facilitates the implementation of millimeter-wave LMBA in monolithic microwave-integrated circuits (MMICs). To validate the design, a GaN MMIC LMBA incorporating the proposed MDL coupler is designed and implemented. The fabricated LMBA can deliver more than 36.35-dBm saturated power at 26 GHz with a drain efficiency (DE) of 35.06% at peak and 24.5% at 6-dB power back-off (PBO). When driven by a 100-MHz fifth-generation (5G) new radio (NR) frequency range 2 (FR2) 64-QAM signal, the proposed LMBA achieves an average output power of 28 dBm, an adjacent channel leakage ratio (ACLR) better than $-$ 47 dBc, and an error vector magnitude (EVM) of $-$ 34.11 dB after digital predistortion.