The effects of bandpass limiters on Mth phase tracking systems in the presence of multiple sinusoidal interferences and additive Gaussian noise are considered. We derive general expressions for the ratio of the output to the input SNR (the SNR ratio) for an Mth-power tracking loop with and without a bandpass limiter. The numerical calculations for the squaring limited and fourth-power limited PLL's in the presence of multiple sinusoidal interferences and noise are carried out, and the results are compared to those for similar loops without limiters. It is found that sinusoidal interference causes the limit of the SNR ratio for infinite carrier-to-noise ratio (CNR) to be no longer consistent with that for only Gaussian noise. The SNR ratio is degraded more as the carrier-to-interference ratio (CIR) decreases and the number of sinusoidal interferences increases. Furthermore, it is found that for the fourth-power PLL, the limiter does not always enhance the output SNR at moderate to strong input SNR's in the presence of sinusoidal interference.
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