Enhancing accuracy in large-signal millimetre-wave measurement systems

Baddeley, Alexander 2025. Enhancing accuracy in large-signal millimetre-wave measurement systems. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

Power amplifiers are essential components in the transmit chain of RF communication systems. Most commercial applications fall within the sub-6 GHz bands, with mobile communication networks being a notable example. Since the inception of these networks, considerable efforts have been made, and continue to be made, in both industry and research to design linear and power-efficient architectures. Techniques employed to improve peak efficiency exploit harmonic terminations, whilst load modulation techniques remain a mainstay for applications requiring signals with a high peak-to-average power ratio (PAPR). There is a growing demand for higher data rates, with new spectrum allocation opening up in the mm-wave bands, enabling advancements in mobile networks and satellite applications. However, this presents numerous challenges, as it is not simply a matter of replicating developments from sub-6 GHz frequencies to mm-wave bands. Numerous challenges exist in device development, including wafer growth and fabrication. System-level engineers must contend with higher path loss and greater signal complexity, while power amplifier designers face the challenge of designing with transistors with lower gain and higher parasitics. This thesis focuses on mm wave characterisation systems, emphasising the improvement of measurement reliability and accuracy. This focus is motivated by the desire to improve the quality of data used to generate device models, which, in turn, can increase the success rate of device tape-outs. This work presents a state-of-the-art mm-wave harmonic load-pull system with waveform measurement capability operating up to 100 GHz. The calibration procedure and configuration of the system to perform waveform measurements are detailed, with a strong focus on achieving accurate and reliable measurements. Mechanical fixtures were designed to support measurement fixtures and avoid any degradation in the phase alignment at the phase meter measurement plane to achieve reliable waveform measurements. For the first time, multi-harmonic load-pull and waveform measurements are demonstrated on a 27.5 GHz GaAs pHEMT, which showed an improvement of power-added efficiency over fundamental tuning of greater than 3%. The primary focus was to ensure reliability and accuracy in practical active and passive mm-wave load-pull systems. It was determined that achieving highly accurate measurements for high-power load-pull requires a dynamic range of 70 dB during the vector calibration stage. However, this is not trivial due to the attenuation needed on the VNA receivers to prevent saturation. Unavoidable calibration errors also arise when configuring a mm-wave system for device measurements. It was shown that mechanical alterations to the system introduce changes to the equivalent network parameters, resulting in load-dependent errors. These effects become more pronounced at higher frequencies. To address this, a second-step method was developed to extend the traditional large-signal calibration procedure. This approach effectively ’recalibrates’ the system in its final measurement configuration. The technique involves performing a load-pull measurement on a thru calibration standard and applying a least-squares fit to the measured waves to determine a new S-parameter matrix, which is then used to recalculate the TRL error box. This technique was demonstrated on the measurement of a GaAs pHEMT at 82.5 GHz, improving the accuracy of the PAE by 8%.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Schools > Engineering
Uncontrolled Keywords:	1. Power Amplifiers 2. mm-wave 3. Calibration 4. Load-Pull 5. Measurements 6. Radio Frequency
Date of First Compliant Deposit:	12 December 2025
Last Modified:	12 Dec 2025 12:49
URI:	https://orca.cardiff.ac.uk/id/eprint/183081

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