EFFECTS OF IMBALANCES AND DC OFFSETS ON I/Q DEMODULATION

Authors
  1. Lee, J.P.Y.
Corporate Authors
Defence Research Establishment Ottawa, Ottawa ONT (CAN)
Abstract
The effects of imbalances and DC offsets, in an I/Q demodulator, on the demodulation of radar signals are addressed in this report. Three normalized parameters, namely the peak-to-peak-ripple to mean, phase error and normalized instantaneous frequency deviation are used to characterize distortions introduced on the envelope, phase and instantaneous frequency respectively. The effect on the distortions, due to aliasing and approximation use in deriving the instantaneous frequency in a discrete-time processor, is also analyzed. When there are imbalances and DC offsets, a bias is produced on both the demodulated envelope and phase. AC ripples with frequency components which are multiples of the baseband frequency are also generated on all of the three demodulated signal waveforms. In EW applications, the instantaneous bandwidth of the I/Q demodulator is usually much wider than the demodulated signal bandwidth. As a result, when the baseband frequency of the signal is high and comparable to its modulation bandwidth, the higher frequency components of the distortion can be effectively reduced by low-pass filtering.
Report Number
DREO-1148 —
Date of publication
01 Dec 1992
Number of Pages
57
DSTKIM No
93-01651
CANDIS No
129728
Format(s):
Hardcopy;Originator's fiche received by DSIS

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