A fully integrated high-efficiency phase-locked sub-terahertz (THz) radiator is reported in this article, implemented in a 55-nm SiGe BiCMOS process. This radiator is capable of generating 192–210-GHz chirps, which can be used for the new generation automotive and imaging radar systems. It consists of a low-power millimeter-wave digital phase-locked loop (DPLL)-based chirp generator, a high-efficiency 6 $\times$ multiplier chain, and an on-chip folded slot antenna. By incorporating a 32-entry lookup table into the millimeter-wave DPLL, a fast back-to-lock feature is realized at the end of each chirp signal. In addition, this chirp generator prototype achieves +5.9/+19.2-dBm sub-THz power/effective isotropic radiated power (EIRP), which is among the highest in all the phase-locked sources at this frequency range. Its 3.0% dc-to-THz efficiency is at least 5 $\times$ higher than all previously published works.