Extending frequency and steering range of amplifier-antenna array via controlled mutual coupling

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School of Electrical Engineering | Doctoral thesis (article-based) | Defence date: 2025-08-22
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Authors

Date

2025

Department

Elektroniikan ja nanotekniikan laitos
Department of Electronics and Nanoengineering

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Mcode

Degree programme

Language

en

Pages

78 + app. 36

Series

Aalto University publication series Doctoral Theses, 134/2025

Abstract

An increasingly connected world demands constant wireless communication and sensing innovation, particularly for next-generation technologies like 5G/6G and novel radars. Such systems require high-performance and reconfigurable radio frequency (RF) front-ends. This doctoral thesis develops a system-level design approach for antennas and amplifiers. The approach in this work is to utilise mutual coupling between antennas and amplifiers rather than trying to avoid and minimise it. Current research moves beyond a traditional component-centric view and adopts an integrated, co-design methodology. The core of this thesis is a simulation framework that analyses coupled antenna arrays with their driving amplifiers, captures their interactions and includes the effects of feeding signals. A C-band pulsed power amplifier that uses GaN technology was developed [I]. The combinatorial feeding scheme [II] enables dynamic power combining and control directly in the air, eliminating the need for lossy power-combining circuits. This framework integrates antenna array modelling, nonlinear amplifier characterisation via load-pull, and a new iterative algorithm. This algorithm considers interelement coupling and nonlinearities and calculates each amplifier’s active impedance. MATLAB’s genetic algorithm was used to optimise signal phases fed to the amplifiers. A custom coupling circuit was used to control coupling levels between antenna elements to allow direct comparison. S-parameters, radiated power, and beam steering range were measured. The system-level design approach demonstrated significant advantages. Studies confirmed frequency range broadening and improved beam-steering of an optimised system, especially at the steering range extremes [III]. To show its efficiency in combining power in the air, a combinatorial feeding scheme was validated [II]. A custom coupling circuit between the amplifiers and antennas resulted in a 92% increase in the operational frequency range in the broadside and a 36% increase in the frequency steer envelope [IV]. This thesis calls for a paradigm shift in RF system design. Substantial improvements in the frequency range, beam-steering, and power efficiency can be achieved if antenna arrays, amplifiers, and feeding signals are considered as an integrated whole. The framework is a powerful tool for designing future reconfigurable RF systems, implying that nextgeneration communication technologies and radars can be more adaptable, efficient, and compact.

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Supervising professor

Viikari, Ville, Prof., Aalto University, Department of Electronics and Nanoengineering, Finland; Aabloo, Alvo, Prof., University of Tartu, Estonia

Thesis advisor

Lehtovuori, Anu, Dr., Aalto University, Department of Electronics and Nanoengineering, Finland

Keywords

amplifier, antenna array, frequency bandwidth, mutual coupling, patch antennas, reconfigurable antenna

Other note

Parts

  • [Publication 1]: J. Kalde, V. Dieves, K. -G. Kruus, E. Amor and A. Aabloo. Small, Economical and Power dense C-Band 350 W Pulsed Power Amplifier. In 19th Biennial Baltic Electronics Conference (BEC), Tallinn, Estonia, 2024, pp. 1-4, October 2024.
  • [Publication 2]: J. Kalde, V. -P. Kutinlahti, A. Aabloo, A. Lehtovuori and V. Viikari. Combinatorial feeding to controlling and combining power on a coupled antenna array. In 17th European Conference on Antennas and Propagation (EuCAP), Florence, Italy, 2023, pp. 1-5, March 2023.
    Full text in Acris/Aaltodoc: https://urn.fi/URN:NBN:fi:aalto-202308014544
    DOI: 10.23919/EuCAP57121.2023.10133101 View at publisher
  • [Publication 3]: J. Kalde, V. -P. Kutinlahti, A. Lehtovuori, A. Aabloo and V. Viikari. Leveraging mutual coupling in antenna-amplifier systems for increased reconfigurability. IEEE Journal of Microwaves, vol. 5, no. 1, pp. 59-67, January 2024.
    DOI: 10.1109/JMW.2024.3499317 View at publisher
  • [Publication 4]: J. Kalde, A. Lehtovuori, A. Aabloo and V. Viikari. Widening frequency envelope of an antenna-amplifier system with coupling structure. IEEE Access, Vol. 13, pp. 656-663, December 2024.
    Full text in Acris/Aaltodoc: https://urn.fi/URN:NBN:fi:aalto-202501151206
    DOI: 10.1109/ACCESS.2024.3520225 View at publisher

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https://urn.fi/URN:ISBN:978-952-64-2637-2

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[diss] Sähkötekniikan korkeakoulu / ELEC