Load-Modulated Hexagonal-Coupler-Based Power Amplifier (LMHA) for Extended Power-Back-off Range

This work presents a new coupler that unleashes an advanced load-modulation architecture, the Load-Modulated Hexagonal-Coupler-based Power Amplifier (LMHA), designed to extend the power back-off (PBO) range required by spectrally efficient 5G/6G modulation schemes. Unlike conventional quadrature couplers, the hexagonal coupler provides six ports and inherently non-uniform S-parameter magnitudes between port pairs, enabling multi-path power combination and higher-order load modulation. These properties make the hexagonal coupler highly favorable for achieving extended PBO. The proposed LMHA consists of one main power amplifier (PA) and four auxiliary PAs. To validate the architecture, we prototyped the hexagonal coupler using transmission lines and implemented LMHA using a Class-AB main PA and (deep) Class-C auxiliary PAs. Experimental evaluation demonstrates efficiency of 56 − 66% at 14 − 16, dB power back-off and 52 − 70% at peak power from 1.7 − 2.1, GHz.