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This paper presents a study of the noise performance of a time-varying impedance matching technique. A mathematical model is developed for calculating the impulse response of the matching design that reconfigures itself in the real time between two subsystems. Based on this model, the signal-to-noise ratio (SNR) degradation of the matching network is defined and analyzed. Simulations of a typical matching design for RL sources show that the SNR degradation is generally lower than 1 dB for common pulse signals including single-cycle sinusoids and Gaussian pulses. Particularly, the time-varying matching design for a high-quality (Q >; 10) source can be optimized to have an impulse response that matches monocycle pulses very well, leading to a near-optimal SNR performance (less than 0.1-dB SNR degradation). The theoretical results are validated experimentally by an implementation of the matching technique for electrically small loop antennas. Lower than 1.5-dB SNR degradation is measured for most cases. The effect of switch noise is also investigated in this paper.