Digital quadrature demodulation of LFM signals obtained by lowpass filtering

Abstract

An effective digital demodulation system based on the technique of Ho, Chan and Inko is designed for quadrature demodulation of signals with a linear frequency modulation (LFM). The influence of LFM-signal parameters on the quality of demodulation is studied. Two variants of a sampling frequency are chosen, and a set of lowpass filters for Q-component generation is designed for each variant of a sampling frequency. The quality of demodulation is estimated in terms of absolute amplitude and phase errors evaluated as a function of system parameters. The results obtained in simulations show that the optimal choice of a sampling frequency (48 MHz) enables to reduce the imbalance phase errors to minimum (0.0012°) if the optimal equiripple lowpass filter with only 6 elements is chosen for Q-component generation. © Springer-Verlag Berlin Heidelberg 2003.