Recursive load modulated balanced amplifier

Yuan, Tonghui 2026. Recursive load modulated balanced amplifier. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

This thesis investigates the Recursive Load-Modulated Balanced Amplifier (RLMBA), a load-modulated power-amplifier architecture intended to combine the broadband impedance-transformation and robustness advantages of balanced amplification with reduced auxiliary-path complexity. Unlike a conventional load modulated balanced amplifier, the RLMBA derives its control signal by sampling a portion of the RF output, applying a controlled phase shift, and re-injecting the resulting signal into the isolated port of the output hybrid. In this way, dynamic load modulation is realised without a dedicated auxiliary control amplifier. The thesis first establishes the theory of operation of the RLMBA. Ideal and lossy analytical formulations are developed to describe how reinjection coupling, loop phase, and passive loss determine the effective device-plane impedance and output-power behaviour. This analysis shows that recursive reinjection can pre serve symmetric load modulation on the balanced devices, while also revealing the sensitivity of the architecture to passive loss and phase accuracy. The results are then validated through two prototype studies. The first proto type demonstrates the practical feasibility of the RLMBA using a sampled-output reinjection loop with discrete delay lines. Broadband simulation and measurement results confirm that recursive reinjection can convert the fixed load trajectory of a conventional balanced power amplifier into a phase-controllable modulation contour and can improve gain, output power, and power-added efficiency over a wide operat ing band. The second prototype develops the concept towards back-off enhancement using an electronically tunable recursive loop.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Schools > Engineering
Uncontrolled Keywords:	1. Broadband 2. Load modulation 3. Balanced amplifier 4. Power amplifier 5. Efficiency improvement
Date of First Compliant Deposit:	1 July 2026
Last Modified:	02 Jul 2026 08:54
URI:	https://orca.cardiff.ac.uk/id/eprint/187847

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