An Analysis of the Phase Coherent - Incoherent Output of the Bandpass Limiter

Abstract

Many applications of the bandpass limiter (BPL) involve coherent demodulation following the limiter. It is shown that as a result of demodulation, the signal mean and the noise variance are direct functions of the phase angle between the signal component passed by the BPL and the coherent reference. As a result, the relationship between the output and input signal-to-noise ratio may be significantly different than that obtained by Davenport for incoherent limiters. A study is also made of the output noise spectral density, and an approximate expressison is derived as a function of the input signal-to-noise ratio, reference phase angle, and the characteristics of the input bandpass filter to the limiter. Also discussed is the first-order signal-plus-noise probability density following coherent demodulation.