A 144GHz 0.76cm-resolution sub-carrier SAR phase radar for 3D imaging in 65nm CMOS

Abstract

Millimeter-Wave-based radar has gained attention in recent years for automotive and object detection applications. Several new applications are also emerging which employ mm-Wave radar techniques to construct short range mm-Wave 3D imaging systems for security screening and biomedical applications. At present, these types of 3D mm-Wave imagers have only been demonstrated in lll-V technology, as CMOS-based radar suffers several range and resolution limitations due to limited output power and linearity.Most CMOS mm-Wave radar systems used in automotive applications are based on Frequency-Modulated Continuous-Wave (FMCW) ranging techniques in which the carrier is swept to produce a frequency offset at the receiver output proportional to the round-trip distance between the radar and target. While FMCW is an excellent approach for accurate ranging, its implementation becomes particularly difficult at high frequencies as the resolution is heavily dependent on sweep linearity and the high RF front-end performance required to support the wideband swept carrier. For 3D mm-Wave imaging applications, this high operating frequency is indispensable as the attainable spatial (XY) resolution is fundamentally limited by the wavelength of the imaging system. Higher frequency also helps relax focusing lens requirements, as the optical diffraction limit is set by the ratio of the radar wavelength over the lens aperture size.