I/Q Demodulation of Radar Signals with Calibration and Filtering,

A simple in-phasequadrature IQ demodulator architecture which can measure the amplitude, phase and instantaneous frequency of radar signals is examined in this report. This architecture has a potential for radar ESM applications where wide instantaneous bandwidth and simple algorithms for extracting the modulation characteristics of radar signals are required. This I Q architecture can meet the requirement by splitting an incoming signal into its in-phase and quadrature components using analog circuitries. However in practice, there are amplitude and phase imbalances between the two components and DC offsets, which can introduce large systematic errors to the measurement. In this report, we present novel techniques which can greatly reduce the systematic errors and improve the accuracy of the measurement. A time-domain analysis on the systematic errors is given. A calibration technique which can be used to correct for the imbalances and offsets is discussed. The effect of noise on the accuracy of the measurement is also examined. Imbalance errors and DC offsets of IQ networks are measured and analyzed. Finally, a post-processing technique employing moving averages, which is shown to be effective for improving the output signal-to-noise ratio and reducing systematic errors, is also presented..