Fully Integrated FMCW Radars: Devices to Systems

This workshop presentation will present the basics of sub-THz FMCW radars and their applications ranging from imaging to metrology. Due to the non-ionizing nature of sub-THz waves, these frequency bands are a safer candidate for biomedical imaging than conventional X-ray imaging systems. In addition, the smaller wavelength of sub-THz waves compared to microwave frequencies provides a sufficient resolution for high-resolution imaging applications. At first, we review the two main imaging techniques that can be implemented by sub-THz FMCW radars: focal-plane imaging and Inverse-Synthetic-Aperture-Radar (ISAR) imaging. System-level and circuit-level design and the pros and cons of each imaging method are presented here. For focal plane imaging, we demonstrate a 168.3GHz FMCW radar chip fabricated on 130nm SiGe BiCMOS technology with 27.5GHz (16.3%) bandwidth and 16.2dBm EIRP. For ISAR imaging, we illustrate a 221.1GHz FMCW radar chip fabricated on 55nm SiGe BiCMOS technology with 62.4GHz (28.2%) bandwidth and 14dBm EIRP. Both radars are used in imaging systems for concealed object detection and hydration sensing. To increase imaging speed, we need to adopt electronic beam scanning in an FMCW radar array instead of conventional mechanical scanning utilized in both imaging techniques mentioned above. However, for having a sub-THz FMCW radar array, we should use a compact radar topology as a unit-cell that can be implemented in a λ/2×λ/2 area on a chip, where λ is the wavelength of sub-THz frequencies in silicon. Therefore, we introduce the autodyne FMCW radar topology that integrates both the TX and RX antennas as well as transmitter and receiver blocks. A unit-cell of 250GHz autodyne FMCW radar is fabricated on 55nm SiGe BiCMOS technology with 66.7GHz bandwidth from 191GHz to 257.7GHz and 17dBm EIRP. In addition, we cover the high-precision metrology application of sub-THz FMCW radars, which can be used in many industries. The definitions of FMCW radar range accuracy and resolution will be presented here. In order to achieve maximum range accuracy and resolution from an FMCW radar, chirp nonlinearities should be compensated. However, when we work with broadband radars with tens of GHz bandwidth, providing chirp linearity is a challenging task that cannot be easily solved with conventional methods. We review the different chirp nonlinearity compensation methods and focus on particle swarm optimization technique as a powerful technique for integrated sub-THz FMCW radars. Then, we employ the 250GHz autodyne FMCW radar in a phase processing method that can provide 54µm (<0.025%) range accuracy for a target at 25.4cm distance. The last part of this workshop presentation will have a quick look at the autodyne FMCW radar array and techniques for improving the phase noise of sub-THz FMCW radars. These new topics will increase the speed and accuracy of imaging and metrology systems.