Estimating noise figure of matching networks for low-input-impedance preamplifiers

The noise figure of a matching network between a receive coil and a preamplifier with low input impedance can be estimated using relationship \(F≈1+R₁₁/R_c\). It is demonstrated how to use this relationship to choose optimal matching-decoupling network topology in terms of signal-to-noise ratio (SNR). The formula serves as an efficient tool to estimate noise figure of matching networks and is useful in low-field and high-coil-Q applications, where the noise of the matching network becomes comparable to coil noise.