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Power Amplifier Design for Wideband Communications

Periodic Reporting for period 1 - PADWIC (Power Amplifier Design for Wideband Communications)

Reporting period: 2015-09-01 to 2017-08-31

Power amplifier (PA) design for wideband communications is a hot topic in electronics, since microwave PAs with high linearity, efficiency and bandwidth represent an enabling technology for wireless/mobile communications enhancement.

Considering the increasing pervasiveness of the wireless infrastructure, research aimed to improve the energy efficiency of wireless devices will impact not only on the telecom industry but on the society as well.

The proposal aims to develop the clipping contours method in continuous modes PAs.
The candidate worked to achieve important objectives:

WP1- Extension the theory of clipping contours to third and higher harmonics
WP2- Creation of a novel design tool for clipping contours in continuous modes
WP3- Development of matching network synthesis techniques to achieve the loads provided by the tool
WP4- Design of PAs prototypes for high power base stations
WP5- Embedding of clipping contours in a Doherty PA prototype
"The project has successfully achieved most of the objectives that were set in the proposal.

In a first phase, the clipping contour method has been extended to the third harmonic using a numerical approach, in Matlab. The results have been presented at the European Microwave Conference 2016, London, in the paper:
- R. Quaglia and S. Cripps, ""Harmonic clipping contours: Numerical computation and extension to higher harmonics,"" 2016 46th European Microwave Conference (EuMC), London, 2016, pp. 405-408. doi: 10.1109/EuMC.2016.7824365

In a second phase, Roberto has been able to re-write the closed form equations of the clipping contours in a novel formulations that allows to insert an arbitrary number of harmonics, thus fulfilling the objectives of WP1. This result, plus the measurements that validate the extended theory, have been published in:
- R. Quaglia, J. J. Bell and S. Cripps, ""New General Formulation and Experimental Verification of Harmonic Clipping Contours in High-Frequency Power Devices,"" in IEEE Transactions on Microwave Theory and Techniques, in printing. doi: 10.1109/TMTT.2017.2687900
Roberto has also collaborated with other members of the Centre for High Frequency Engineering in the work published in:
R. Quaglia, D. J. Shepphard and S. Cripps, ""A Reappraisal of Optimum Output Matching Conditions in Microwave Power Transistors,"" in IEEE Transactions on Microwave Theory and Techniques, vol. 65, no. 3, pp. 838-845, March 2017. doi: 10.1109/TMTT.2016.2627557

The objectives of WP2, WP3 and WP4 have been also achieved in large part. Roberto has embedded the Clipping Contour design tool in ADS and MWO, two of the most diffused CAD software among PA designers. The tool has been useful in designing a number of prototypes, in particular to estimate, during the design, the amount of clipping that the active device was experiencing during its operation. The most prominent result has been the design of an integrated Doherty PA, in collaboration with the US foundry Qorvo Inc. The state-of-the art performance of the fabricated device have been presented at the International Microwave Symposium 2017, Honolulu, US, in the paper:
R. Quaglia, M.D. Greene, M.J. Poulton and S.C. Cripps, ""Design and characterization of a 1.7–2.7GHz quasi-MMIC Doherty power amplifier,"" International Microwave Symposium 2017.

PADWIC has progressed the knowledge on power amplifiers theory and design thanks to the novel formulation of clipping contours and its implementation in a design tool.

Moreover, the research on saturated contours has also led to a new technique to trace power and efficiency contours for high frequency devices in compressed regime.

The research has shown its potential impact on the industry when a Doherty power amplifier, fabricated in quasi-MMIC technology in collaboration with Qorvo Inc, has been successfully tested showing state of the art performance. The invented tools are being used in the design inside the Centre for High Frequency Engineering at Cardiff University, and are easily reproducible by anyone interested since the publications are available as Open Access documents. For this reason, the impact of this research on further research and industrial application is expected to be important.

During PADWIC, the Fellow has organized three workshops at the main International Conferences in Microwave Electronics. This has allowed to attract an audience wider than usual to the subject of waveform engineering. These initiatives have permitted a better dissemination of the results among the scientific and industrial community.