A millimeter-wave (MMW) radar system is promising for high-precision imaging because of its short wavelength and broad range of available bandwidths . Particularly in the frequency range of 92-100 GHz, where the US, the EU, and Japan allow radiolocation, an atmospheric attenuation coefficient of 0.4 dB/km in standard atmospheric conditions limits the imaging range. Thus, a distributed radar system directly connected to optical fiber networks realizes both high-precision imaging and a large imaging area. A frequency-modulated continuous-wave (FM-CW) radar system based on an optical modulation technique has already been reported and evaluated in the optical domain . In this paper, we evaluate the precision of a broadband FM-CW radar system operated with optical modulation technology. A broadband in-phase/quadrature (IQ) mixer can directly convert to intermediate frequency signals with a common-mode rejection feature .