Mitigating interference from switch-mode power supplies in sampling receivers

The research and development preliminaries, which led to an opportunity to embark on the present study took place during the system testing phase of a frequency-modulated continuous wave (FMCW) radar at Reutech Radar Systems, when a large false target was observed emerging on the range-Doppler map. The first indication was that the problem originated from interference caused by the switch-mode power supply (SMPS), which supplies direct current power to the radar receiver subsystem. This created the need for a new DC power supply, which was able to minimise the interference itself and mitigate the effects of the interference caused by the switching of the power supply. The present study is based on the research and development of techniques to mitigate interference from SMPS in sampling receivers, with emphasis on FMCW radar receiver applications. The study was divided into four main sections: research, simulation, design and evaluation. The research involved obtaining background information on sampling receivers, sampling theory, range-Doppler processing, SMPS, their effects, and mitigating these. This research section was utilised to simulate the various interference mitigation techniques, while a power supply printed circuit board (PCB) was established in the design phase to practically illustrate the techniques being utilised. Lastly, during evaluation, this PCB was evaluated against the criteria set out in the research phase. The results demonstrated that the techniques of synchronising the pulse width modulation clock to the sampling frequency and sweep repetition frequency yielded a significant reduction in the SMPS noise on the range-Doppler map. This technique may also be applied in other electronic sampling systems which perform digitisation of the input data, such as analogue-to-digital converters.