Noncircularity of Demodulated Radar Signal

The output of the quadrature demodulator is generally regarded as a complex signal that is circular if only the demodulator is well balanced. In the paper we analyze properties of quadrature demodulators, particularly digital one, and show that the output is noncircular also if the input signal is nonstationary. Then we find sources of this noncircularity and show that they stem from transients of the low-pass demodulator filter. This is quite important because nonstationary inputs are quite typical in radar where power of echoes depends strongly on range. In the first sections we also review complex random signals and properties of circularity and properness.