Wideband I/Q demodulators: measurement technique and matching characteristics

Wideband I/Q demodulators which can be used to measure the amplitude, phase and instantaneous frequency of radar signals are investigated. A simple Fourier transform technique is developed to characterise the imbalances and DC offsets of I/Q demodulators by injecting a test signal. Imbalances and DC offsets are minimised using component matching and calibration techniques. Average RMS fractional amplitude and phase imbalance errors of 0.011 and 0.302 degrees, respectively, can be achieved on custom matched units at a centre frequency of 1 GHz over an instantaneous bandwidth of 100 MHz and a dynamic range of 24 dB. Finally, the matching characteristics over time and temperature on some of these wideband I/Q demodulators are also evaluated.