Scientific Context and Motivation

Future space communication payloads, high-resolution radars, and active Earth-observation instruments increasingly rely on millimeter-wave (mm-wave) and sub-THz frequency bands to meet growing demands in bandwidth, spectral efficiency, and data throughput.

Operating in the Ka- and Q-bands (30–50 GHz) enables compact, high-gain antennas and multi-beam architectures but also imposes stringent requirements on power amplifier linearity, efficiency, and thermal robustness.

Among semiconductor technologies, GaN high-electron-mobility transistors (HEMTs) are the key enablers of these systems, combining high power density, radiation hardness, and wide-bandgap stability. However, optimizing linearity–efficiency trade-offs at mm-wave frequencies remains a major scientific and technological challenge.

In particular, device-level nonlinear characterization tools are still limited, especially for two-tone or modulated excitations at frequencies beyond 30 GHz, where classical single-tone load-pull methods fail to predict intermodulation behavior and distortion mechanisms.

This PhD project will be conducted at the Institut d’Électronique, de Microélectronique et de Nanotechnologie (IEMN, Lille) with the aim of addressing this gap by developing and exploiting an advanced two-tone active load-pull measurement system for GaN HEMTs operating around 40 GHz, targeting space-qualified power amplifier applications.

The laboratory offers access to state-of-the-art on-wafer RF measurement facilities, clean-room fabrication, and high-frequency design tools.

Objectives of the PhD

The research will combine experimental microwave engineering, nonlinear device modeling, and system-level validation.

The main objectives are:

Develop and optimize an active two-tone load-pull bench up to 40 GHz capable of synthesizing independent impedances at each tone directly at the device plane, with high power and phase accuracy.

Integration of phase-locked dual-source excitation, custom band-pass filtering to suppress bench-generated IM3, and per-tone active load control.

Full vector and power calibration traceable to the DUT plane, ensuring metrological accuracy.

Characterize advanced GaN HEMT structures (including AlN/GaN/AlGaN and graded or carbon-doped channels) fabricated on SiC or GaN-on-Si substrates.

Extract C/IM3, PAE, and OIP3 metrics across bias and frequency conditions relevant to space communication payload amplifiers.

Identify memory effects, IM3 asymmetry, and thermal trapping phenomena under continuous-wave and pulsed excitation.

Model and predict linearity behavior using physics-based nonlinear models and behavioral envelope simulations validated by measurements.

Correlate the measured intermodulation response with transconductance derivatives, trap dynamics, and thermal time constants.

Provide design guidelines for linearization-friendly device topologies and matching networks.

Assess space applicability by evaluating the temperature dependence, robustness, and repeatability of linearity metrics under representative operating conditions (temperature cycles, pulsed regimes).

Expected Contributions

The thesis will deliver:

A validated two-tone active load-pull measurement platform up to 40 GHz, unique in France, usable by CNES and partner laboratories for future payload developments.

A comprehensive experimental database of linearity–efficiency characteristics for state-of-the-art GaN HEMTs suitable for Ka- and Q-band satellite transmitters.

Improved physical understanding of IM3 generation and memory effects in GaN transistors under realistic drive conditions.

Compact behavioral and empirical models that can be directly implemented in RF system simulations of spaceborne amplifiers, enabling distortion prediction and linearization strategies.

Dissemination through high-impact publications (IEEE T-MTT, IEEE T-ED, ARFTG, EuMW) and knowledge transfer to CNES partners.

Scientific and Industrial Impact

For CNES, this project directly supports the development of next-generation high-frequency payloads with enhanced spectral efficiency and power management, crucial for telecommunication satellites, inter-satellite links, and radar imaging systems.

It also strengthens the French and European expertise in nonlinear microwave metrology and GaN device modeling, key enablers for sovereign space technology.

From a broader scientific standpoint, the PhD will bridge device physics, microwave measurement science, and system-level design, training the candidate in both experimental hardware development and advanced RF modeling—skills of strategic importance to the space sector.

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For more Information about the topics and the co-financial partner (found by the lab !); contact Directeur de thèse - farid.medjdoub@iemn.fr

Then, prepare a resume, a recent transcript and a reference letter from your M2 supervisor/ engineering school director and you will be ready to apply online  before March 13th, 2026 Midnight Paris time !