Page 220 - Fundamentals of Radar Signal Processing

generation of in-phase and quadrature signals. (After Shaw and Pohlig, 1995.)

FIGURE 3.23 Spectra corresponding to successive signals in the digital I/Q
system of Fig. 3.22. (a) Spectrum of bandpass input signal with information
bandwidth of β Hz, (b) result of translation to an IF frequency of 0.625β, (c) one
period of spectrum on normalized frequency scale after A/D conversion, (d)
digital complex modulation centers the lower sideband at DC, (e) only the
lower sideband remains after lowpass filtering, (f) decimation by two reduces
the sampling rate to 1.25β. (After Shaw and Pohlig, 1995.)

The next step is to lowpass filter to remove the upper sideband,
leaving only the baseband portion of the spectrum. A 16-point finite impulse