Wideband Single-Input Load-Modulated Double Balanced Amplifier With Intrinsic Load Insensitivity

This paper presents the first-ever wideband loadmodulated double balanced amplifier (LMDBA) with an intrinsic isolation to load. Building upon the foundational concept of the generic load modulated balanced amplifier (LMBA), by setting the control amplifier (CA) to balanced topology, the LMDBA can inherit the load-mismatch tolerance characteristic of balanced amplifiers, eliminating the need for a magnetic circulator. To demonstrate the principle, a wideband RF-input LMDBA is developed using GaN devices and commercial branchline quadrature hybrid couplers from 1.9-2.7 GHz. The experimental results exhibit an efficiency of 54-75 % at peak power and 45-60 % at 10-dB output back-off (OBO) under the matched condition of load across the band. An efficiency up to 70.2 % at peak power and up to 54.2 % at 10-dB OBO are measured under 2:1 VSWR of load. Additionally, the PA's linearity profiles (AMAM and AMPM) can be well maintained against load mismatch compared to matched condition without reconfiguration. In modulated measurement, the efficiency and linearity performance can well maintained under various load as well.