Output Signal Re-Injection in Load-Modulated Balanced Amplifiers for RF Bandwidth Improvement

This letter discusses the theory, simulation, and experimental characterization of a load-modulated balanced amplifier (LMBA) where the control signal power (CSP) is obtained by re-injecting part of the output RF signal. Compared to the standard balanced load-modulated power amplifier (PA), this approach does not require an external amplification of the CSP. The potential of this technique is explored experimentally with a balanced PA (BPA) working on 1400-3400-MHz band, using an external off-the-shelf directional coupler and manual phase shift adjustment. The induced load modulation can lead to a 10% increase of power added efficiency, or 1 dB of output power, across the frequency band of operation compared to the BPA.