Thesis title: Power Amplifiers for 5G Sub-6GHz (FR1) Applications
Fifth-generation (5G) New Radio (NR) sub-6 GHz (FR1) transmitters, impose stringent
and often conflicting requirements on radio-frequency (RF) power amplifiers (PAs). On the
one hand, high average efficiency is needed to reduce heat dissipation and power consumption;
on the other hand, the large Peak-to-Average Power Ratio (PAPR) of modern waveforms
demands that PAs preserve efficient operation under output power back-off, while
maintaining adequate linearity and spectral cleanliness. In addition, multi-band operation
and the resulting growth of RF front-end complexity, make compact and practically implementable
solutions increasingly important. Within this framework, this thesis investigates
design methodologies and circuit topologies for GaN power amplifiers targeting 5G NR FR1
band n78, with a center frequency of 𝑓𝑐 = 3.6 GHz and operation over the 3.3–3.8 GHz
region, with particular emphasis on maximizing conversion efficiency while analyzing its
impact on linearity-related constraints. The research focuses on two well-established highefficiency
approaches: Harmonic Tuning (HT) techniques (up to the third harmonic) and
the Doherty Power Amplifier (DPA) architecture. The work establishes practical, step-bystep
design guidelines, grounded in theoretical analysis and validated through circuit-level
simulations and experimental measurements. A packaged 10 W GaN HEMT device (Cree
CG2H40010) implemented in a hybrid technology on Rogers RT/duroid 6010.2LM (10.7
dielectric constant), is adopted as the reference active device and platform. Such a high
dielectric constant has been chosen to make the dimension of all the circuits smaller. The
baseline design is a single-stage deep Class-AB PA employing Multi-Harmonic Tuned Terminations,
intended for macro- and micro-cell transmitter applications. This amplifier is
designed and optimized within a 5G-relevant bandwidth (3.4–3.7 GHz), and then simulated
and experimentally characterized. Measured results confirm that the proposed harmonictuned
solution satisfies the targeted 5G-oriented performance goals, achieving a peak output
power not lower than 40 dBm and an average efficiency exceeding 47% under representative
operating conditions. Starting from the measured harmonic-tuned prototype as a reference,
three additional single-stage PA configurations are designed under the same technological and
biasing conditions, in order to provide a consistent comparison of harmonic manipulation
strategies. Specifically, the following architectures are considered: (i) Class-AB Tuned-Load,
(ii) Class-AB Tuned-Load with second- and third-harmonic input short terminations, and
(iii) Class-F. All candidates employ harmonic engineering, and their behavior is benchmarked
through continuous-wave (CW) simulations across the target band. The comparative study
highlights the advantages of Multi-Harmonic Tuned Terminations as a particularly effective
solution to maximize delivered power and efficiency over a 5G sub-6 GHz bandwidth, while preserving a design flow that remains compatible with practical implementation constraints
(e.g., matching-network complexity and feasibility in hybrid technology). To further
strengthen the design methodology, an alternative verification approach is also proposed to
assess the consistency and accuracy of the results obtained through the theoretical synthesis
process. Finally, the thesis extends the investigation to load-modulated architectures by
analyzing the Doherty principle in a comprehensive manner and applying it to the design
of a two-way DPA for 5G FR1 operation. A complete design procedure is developed and
applied to a DPA operating in the 3.4–3.8 GHz band, including the key matching and combining
networks required for correct load modulation. CW simulations are used to evaluate
performance and compliance with 5G-driven specifications, confirming that harmonic-tuned
single-stage PAs and the Doherty architecture constitute viable and effective choices for
meeting the efficiency and output power requirements of 5G sub-6 GHz transmitters.